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Chemoautotrophy in large organisms?

Chemoautotrophy in large organisms?



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The major nutritional mechanisms include chemoautotrophy, heterotrophy (including parasitism and saprotrophy) and photoautotrophy. All of these modes of nutrition developed first in prokaryotic ancestors, and gradually, through the course of evolution, these prokaryotes formed complex eukaryotic, multicellular organisms. Some of these complex descendants (the majority of Kingdom Plantae) possessed the photoautotrophic mode and some (the majority of Kingdom Animalia, some of Kingdom Protista & Kingdom Fungi) possessed the heterotrophic mode.

My question is, since all the three modes developed quite early in evolutionary history, why didn't any chemoautotrophic multicellular, eukaryotic organism develop? (Or, if they did, why did they not form a wide-diverse group as the organisms with other two modes of nutrition did.)

(One possible reason could be lesser availability of chemoautotrophic substrates, but I have no proof, nor any argument to support this.)


I've been thinking about this question for a few days and along the lines of @ThomasIngalls comment, the simple answer is that cooperation between organisms has such a huge advantage in selection that any chance a eukaryote would become a chemautotroph would simply not adapt fast enough to compete with those that are already holding these niches.

The chemautotrophs I'm aware of are usually archaeabacteria. They are optimized to grow slowly and have a large number of genes that can break down the unusual chemical compounds to grow in an inorganic often anoxic environment. These bacteria have genes evolved from the chemautotrophic earliest days of life on earth. They live deep within the earth, under ground, in volcanic vents. There are animals that live in some of these environments, but its simply too easy for these to use the bacteria that are already growing here readily rather then re-evolve the genes to do it by themselves.

Eukaryotes are already symbiotes - they used bacteria to create ATP and photosynthetically fix carbon to the extent that they absorbed them as mitochondria and chloroplasts respectively. If eukaryotes were under a tremendous amount of selective pressure, some of them might absorb symbiotic chemautotrophs, but without such pressure, it doesn't happen when you are competing against plants with roots and animals that eat for their energy.

Forming systems of organisms is much more stable than having individual species that can do it all. This question is actually similar to other questions that ask why we don't have metal armor, run as fast as cheetahs, etc. Evolution doesn't actually create super animals that are completely self contained. The ones that reproduce the best are the ones that can actually spread out the risk of survival and contribute to an ecosystem.

It kind of makes me think of human beings - the only superorganism on the planet in this regard. We don't really need to compete against any organism - we are in fact killing most of them out there without really thinking about it. That might now turn out to be good for us long term.


Chemoautotroof

The canonical network of autotrophic intermediary metabolism: minimal metabolome of a reductive chemoautotroph We also asked whether the relative abundance of chemoautotrophs and methanotrophs includes an ontogenetic factor What are chemoautotrophs? What are some examples? Update Cancel. One example of a chemoautotroph would be iron bacteria (Thiobacillus Ferrooxidans) The expansion of gene families related to immune recognition, endocytosis and caspase-mediated apoptosis indicates the mussel's adaptation to the presence of chemoautotrophic endosymbionts in its gills

Chemoautotroph - Definition, Function and Examples Biology

Chemoautotrophic definition is - being autotrophic and oxidizing an inorganic compound as a source of energy. How to use chemoautotrophic in a sentence. being autotrophic and oxidizing an inorganic compound as a source of energ A chemoautotroph is an organism that uses inorganic energy sources for food. Then it puts together its own organic compounds using ATP . Chemoautotrophs are mostly bacteria or archaea that live in hostile environments such as deep sea vents Biology-online is a completely free and open Biology dictionary with over 60,000 biology terms. It uses the wiki concept, so that anyone can make a contribution

Video: Chemoautotroph definition of chemoautotroph by Medical

What are chemoautotrophs? What are some examples? - Quor

  • Learn more about. Chemoautotroph Download as PDF. Set alert. 16 Handling of Psychrophilic Microorganisms. Nick J Russell, Don A Cowan, in Methods in Microbiology, 2006
  • Video: Chemoautotrophs: Definition & Examples We are going to get a working definition of chemoautotroph and look at some examples of organisms that are classified as chemoautotrophs
  • chemoautotroph definition: noun See chemolithoautotroph. Related Forms: 1. che′mo·au′to·troph′ic adjective 2. che′mo·au·tot′ro·phy noun. Definition

Video: Chemoautotrophic - The Free Dictionar

Definition of CHEMOAUTOTROPHIC - Merriam-Webste

Other articles where Chemotroph is discussed: bacteria: Nutritional requirements: Chemotrophs obtain their energy from chemicals (organic and inorganic compounds) chemolithotrophs obtain their energy from reactions with inorganic salts and chemoheterotrophs obtain their carbon and energy from organic compounds (the energy source may also serve as the carbon source in these organisms) Photoautotroph definition, any organism that derives its energy for food synthesis from light and is capable of using carbon dioxide as its principal source of carbon

Bill Nye discusses the discovery of hydrothermal vents on the ocean's floor 2007) among these, the reductive TCA cycle (rTCA) is the pathway utilized by many reductive chemoautotrophs (Fuchs, 1989 Nakagawa and Takai, 2008). Also presented is a compilation of biochemical reactions and a list of metabolites enumerating a representative minimal metabolome of a free-living reductive chemoautotroph Learn More about chemoautotroph. Share chemoautotroph. Resources for chemoautotroph. Time Traveler! Explore the year a word first appeared In contrast to photoautotrophs, photoheterotrophs are organisms that depend solely on light for their energy and principally on organic compounds for their carbon. . Photoheterotrophs produce ATP through photophosphorylation but use environmentally obtained organic compounds to build structures and other bio

Types of Metabolism Photoautotrophs and Photoheterotrophs Photoautotrophs and photoheterotrophs are organisms that rely on light as their source of energy to carry out cellular processes In this video, Biology Professor (Twitter: @DrWhitneyHolden) discusses heterotrophs, autotrophs, phototrophs, and chemotrophs and how these categories are used to describe different ways that.

chemoautotroph (plural chemoautotrophs) ( biology ) a simple organism , such as a protozoan , that derives its energy from chemical processes rather than photosynthesis Synonyms [ edit Another type of chemoautotroph is the iron bacteria. These bacteria are most commonly encountered as the rusty coloured and slimy layer that builds up on the inside of toilet tanks Which organism is NOT correctly matched to its energy source? A) Photoheterotroph — light B) Photoautotroph — CO2 C) Chemoautotroph — Fe2 Autotroph vs. Heterotroph Diffen › Science › Biology Autotrophs are organisms that can produce their own food from the substances available in their surroundings using light ( photosynthesis ) or chemical energy (chemosynthesis)

A chemoautotroph. C. Neither of the above. D. No one knows. Answer to Question #3. D is correct. We have no direct evidence of the first form of life on Earth, and it. chemoautotrophy (uncountable) ( biology ) A mode of growth in which CO 2 is the exclusive source of assimilated carbon, and energy is derived from chemical processes rather than light. Related terms [ edit Chemoautotroph. Organism that makes organic carbon molecules from carbon dioxide using energy from chemical reactions. Chemo, Auto, Photo, Hetero study guide by.

Chemoautotroph - Simple English Wikipedia, the free encyclopedi

  1. Apart from chemoautotrophy and suspension feeding there is a third possible strategy, epidermal uptake of dissolved organic matter (DOM). The morphology of bacterial symbioses in the gills of mussels of the genera Adipicola and Idas (Bivalvia: Mytilidae
  2. Definition of chemoautotroph - an organism, typically a bacterium, which derives energy from the oxidation of inorganic compounds
  3. A chemosynthetic organism that obtains energy from the oxidation of inorganic compounds and uses carbon dioxide as its sole source of carbon for growth. Also called chemoautotroph. Also called chemolithotroph
  4. A chemoautotroph d)makes food molecules using chemical energy. The definition of a chemoautotroph or chemotroph is an organism that obtains energy by the oxidation of electron donors in their environments. They can be either organic or inorganic molecules

What Are Examples of Chemoautotrophic Bacteria? Nitrosomonas and iron bacteria are the most common examples of chemoautotrophic bacteria because they are able to produce energy through a chemical process, according to Dr. John W. Kimball A chemoautotroph is an organism that produces its cellular energy, usually in the form of ATP, directly from the environment using a chemical source. There are a number of groups of bacteria that produce energy this way

Photoautotroph - Biology-Online Dictionary Biology-Online

Study Chapter 5 flashcards taken from chapter 5 of the book Microbiology: An Introduction. Sign in. Sign in. chemoautotroph - Fe2+ D) chemoheterotroph - glucose A chemoautotroph is an organism that uses inorganic energy sources. Then it puts together its own organic compounds using ATP . Chemoautotrophs are mostly bacteria or archaea that live in hostile environments such as deep sea vents

d. chemoautotroph. 2. In the organism described in the previous question, what would be the waste products of its catabolic reactions? a. CO2 and H2O b. H2SO4 c. O2 and H2SO4 d. organic fermentation products. 3. As a microorganism of a given shape increases in size its surface area grows much more _____ than does its volume. a. quickly b. These organisms are called chemolithotrophs or chemoautotrophs. Chemolithotrophy is widespread in the two domains of prokaryotes: the Bacteria and the Archaea. Many chemolithotrophs use molecular oxygen as electron acceptor, but chemolithotrophy is also possible in the absence of oxygen How do chemoautotrophs make energy? A) They convert carbon dioxide, water, and inorganic compounds into carbohydrates. B) They covert carbon dioxide, water, and sunlight into carbohydrates

Chemoautotroph - an overview ScienceDirect Topic

  1. Chemoautotrophs are organisms that obtain their energy from a chemical reaction (chemotrophs) but their source of carbon is the most oxidized form of carbon, carbon dioxide (CO2)
  2. 2005), and Riftia has been shown to store enough oxygen and sulfide to sustain chemoautotrophy for hours without environmental input (Arndt et al
  3. Chemoautotroph That is an organism that makes its own energy from chemicals. Chemosynthetic bacteria for example, do this and they are found on the hydrothermal vernts along the MId Ocean Ridge
  4. How Do Chemoautotrophs Obtain Energy? Chemoautotrophs obtain energy by using oxygen or compounds with high oxygen content to oxidize, or take electrons from, sulfur compounds, hydrogen, elemental sulfur, ammonia or metals
  5. Zoran Ivanovic, Marija Vlaski-Lafarge, in Anaerobiosis and Stemness, 2016. 8.1 From the First Prokaryotes to the Great Oxidation Event. According to the actual evidence-based knowledge, the first simple organisms (prokaryotes) appeared on Earth about 3.8 billion years ago and evolved in completely anoxic conditions
  6. Distinguish between photoautotrophs and chemoautotrophs? Chemoautotroph, also called chemotroph, is a type of autotroph that can make organic materials from inorganic chemical compo.

Study Chapter 11 flashcards. Play games, take quizzes, print and more with Easy Notecards. a chemoautotroph. D) a photoautotroph. E) a photoheterotroph Best Answer: The answers given are very good. By strict definition, a chemoautotroph derives energy from the oxidation of reduced (usually inorganic) molecules (like H2S) and uses Carbon dioxide as its carbon source What is the difference between Phototrophs and Chemotrophs What are Phototrophs The organisms which perform proton capturing in order to acquire energy are known as phototrophs

Chemoautotrophs: Definition & Examples - Video & Lesson

A chemoautotroph is an organism that produces its cellular energy, usually in the form of ATP, directly from the environment using a chemical source What does chemoautotroph mean? Definitions for chemoautotroph chemoau·totroph Here are all the possible meanings and translations of the word chemoautotroph The canonical network of autotrophic intermediary metabolism: minimal metabolome of a reductive chemoautotroph. Analysis of the intermediary metabolism of a reductive chemoautotroph We have adopted this strategy in the comparative analysis of metabolic pathways for the above-mentioned organisms in order to construct the canonical metabolic. Escherichia Coli The bacteria known as E. coli are examples of the prokaryotic cell type. Comparison of Eukaryotic and Prokaryotic Cells: Index Reference Enger & Ross About This Quiz & Worksheet. Chemoautotrophs are an interesting group of organisms. This quiz and worksheet combo will help you understand the uniqueness of these organisms and ensure you.

Chemoautotroph dictionary definition chemoautotroph define

  1. -Which of the chemoheterotroph, chemoautotroph and chemolithotroph organisms, use inorganic molecules as electron donor and electron acceptors? 3-Photosynthesis -What is the purpose of photosynthesis (photoS)
  2. B) Chemoautotroph - Fe2+ C) Chemoheterotroph - glucose D) Photoheterotroph -light E) Chemoautotroph - NH3 . 4) How many molecules of A TP can be generated from the complete oxidation of glucose to CO2 and H2O? A) 76 B) 34 C)4 D) 38 E) 2 . 5) Which of the following is not true about anaerobic respiration? A) It involves the Krebs cycle
  3. As nouns the difference between photoautotroph and chemoautotroph is that photoautotroph is (biology) an organism, such as all green plants, that can synthesize its own food from inorganic material using light as a source of energy while chemoautotroph is..

Chemotroph biology Britannica

Iron bacteria: This is an example of a chemoautotroph, and receive their energy from the oxidation or breakdown of various organic or inorganic food substances in their environment. Iron bacteria is a specific example of this type of autotroph Figure 5.6 33) The rates of O 2 and glucose consumption by a bacterial culture are shown in Figure 5.6. Assume a bacterial culture was grown in a glucose medium without O 2..

, equivalent, same meaning and similar words for the term chemoautotroph A) photoheterotroph light B) photoautotroph CO2 C) chemoautotroph Fe2+ D) chemoheterotroph glucose E) chemoautotroph-NH3 Answer: B Test Bank Go!—all FREE!! Hom

Photoautotroph Define Photoautotroph at Dictionary

c) chemoautotroph. d) chemoheterotroph . 4. An obligate halophile requires high: a) pH. b) temerperature. c) salt. d) pressure . 5. Chemoautotrophs can survive on _____alone. a) minerals. b) CO 2. c) minerals and CO 2. d) methane . 6. Which of the following statements is true for all organisms? a) they require organic nutrients. b) they require. Nutrition & Growth. Substances required by living organisms in relatively large quantities and which play principal roles in cell structure and metabolis What is the difference between autotroph, phototroph, and chemolithotroph? So the four major divisions are Chemoautotroph, Chemoheterotroph, Photoautotroph, and.

Chemoautotrophic eukaryotic cells? (Here, chemotroph and chemoautotroph are the same things) But Generally the 2nd Classification is preferred, because. Chemoautotroph Most are bacteria or archaea that live in hostile environments such as deep sea vents and are the primary producers in such ecosystems . An example of one of these prokaryotes would be Sulfolobus is that chemoautotroph is (biology) a simple organism, such as a protozoan, that derives its energy from chemical processes rather than photosynthesis while lithotroph is (biology) an organism that obtains its energy from inorganic compounds (such as ammonia) via electron transfer Keywords Ruminant digestion Symbiosis Definition Algal-invertebrate Chemoautotroph-invertebrate Hydrothermal vent H2S (sulfide) chemoautotrophy Basic parts of alimentary canal Structure of cellulose Cecum Allows breakdown of cellulose in herbivores One opening and exit - lower oxygen, slower passage Digested cellulose must be reintroduced to.

Chemoautohtroh are also included in the auotroph group but unlike the plants wich are fotoautotroph they are called chemoautotroph because of their property of extracting their energy (ATP) from chemical reactions i.e. when iron 2 oxides into iron3 chemoautotroph: a simple organism, such as a protozoan, that derives its energy from chemical processes rather than photosynthesis The Importance of Photosynthesis The processes of all organisms—from bacteria to humans—require energy 9/14/2016 AP Bio Chapter 27 Flashcards | Quizlet 1/4 AP Bio Chapter 27 36 terms by msaux2 Anaerobic respiration the use of inorganic molecules other than oxygen to accept electrons at the downhill end of the electron transport chains Biofilm a surface-coating colony of prokaryotes that engage in metabolic cooperation Bioremediation the use of.

All extant life forms depend, directly or indirectly, on the autotrophic fixation of the dominant elements of the biosphere: carbon, hydrogen, nitrogen, oxygen, phosphorus, and sulfur. We have earlier presented the canonical network of reactions that constitute the anabolism of a reductive chemoautotroph An autotroph is an organism able to make its own food. Autotrophic organisms take inorganic substances into their bodies and transform them into organic nourishment. Autotrophs are essential to all life because they are the primary producers at the base of all foo

Hydrothermal Vents - YouTub

  1. The translations of chemoautotroph from English to other languages presented in this section have been obtained through automatic statistical translation where the essential translation unit is the word «chemoautotroph» in English
  2. Chapter 11 - PROKARYOTES: Survey of the Bacteria & Archaea 2. The Archaea 1. The Bacteria. Important Metabolic Terms • chemoautotroph - gets energy from.
  3. MICROBIAL METABOLISM Chapter 6, pp 1 29-166 I. Metabolism = sum of anabolic and catabolic pathways (Fig 6-1, p13 0) A) anabolism = to build up, generally requires energy B) catabolism = to break down, may release energy Cells generally use energy from catabolic pathways to drive anabolic pathways, and the high energy intermediate here is.
  4. A) chemoautotroph-NH_B) chemoautotroph - Fe__C) photoautotroph - CO_D) photoheterotroph - lightE) chemoheterotroph - glucose Front Reveal the answer to this question whenever you are ready
  5. This flashcard is meant to be used for studying, quizzing and learning new information. Many scouting web questions are common questions that are typically seen in the classroom, for homework or on quizzes and tests
  6. Metabolism of the methanogens is absolutely unique, yet methanogens represent the most prevalent and diverse group of Archaea. Methanogens use H 2 and CO 2 to produce cell material and methane. They have unique coenzymes and electron transport processes
  7. Definition of chemoautotroph in US English - an organism, typically a bacterium, which derives energy from the oxidation of inorganic compounds

The bacterium E. coli requires simple organic molecules for growth and energy-it is therefore a: A) Chemoautotroph B) Chemoheterotroph C) Lithotroph D) Photoautotroph E) Photoheterotroph The pH of a sample of water is 7.0, while lime juice is pH 2.0 Photoautotrophs must balance their excitation capture with metabolic energy consumption in the face of fluctuations in light, UV, temperature, and nutrients over a range of time scales

An autotroph is an organism able to make its own food. Autotrophic organisms take inorganic substances into their bodies and transform them into organic nourishment. Autotrophs are essential to all life because they are the primary producers at the base of all food chains Acidithiobacillus ferrooxidans PubMed Genome of ATCC 23270 Genome of ATCC 53993 Description and Significance A. ferrooxidans is a Gram negative rod shaped bacterium that is commonly found in deep caves or acid mine drainage, such as coal waste (10, 11, 12) This is Part 3 of a six-part series telling the story of humankind's efforts to understand the origins of life by looking for it in extreme environments where life thrives without relying on the. chemoautotroph - 1 definition - noun: 1. chemoautotroph -- An organism, such as a bacterium or protozoan, that obtains its nourishment through the oxidation of inorganic chemical compounds as opposed to photosynthesis Other articles where Chemoheterotroph is discussed: bacteria: Nutritional requirements: reactions with inorganic salts and chemoheterotrophs obtain their carbon and energy from organic compounds (the energy source may also serve as the carbon source in these organisms) Chemoautotrophic Carbon Fixation Rates and Active Bacterial Communities in Intertidal Marine Sediments isolated from the ammonia-oxidizing chemoautotroph.


Contents

Hydrothermal vents in the deep ocean typically form along the mid-ocean ridges, such as the East Pacific Rise and the Mid-Atlantic Ridge. These are locations where two tectonic plates are diverging and new crust is being formed.

The water that issues from seafloor hydrothermal vents consists mostly of sea water drawn into the hydrothermal system close to the volcanic edifice through faults and porous sediments or volcanic strata, plus some magmatic water released by the upwelling magma. [1] In terrestrial hydrothermal systems, the majority of water circulated within the fumarole and geyser systems is meteoric water plus ground water that has percolated down into the thermal system from the surface, but it also commonly contains some portion of metamorphic water, magmatic water, and sedimentary formational brine that is released by the magma. The proportion of each varies from location to location.

In contrast to the approximately 2 °C (36 °F) ambient water temperature at these depths, water emerges from these vents at temperatures ranging from 60 °C (140 °F) [5] up to as high as 464 °C (867 °F). [6] [7] Due to the high hydrostatic pressure at these depths, water may exist in either its liquid form or as a supercritical fluid at such temperatures. The critical point of (pure) water is 375 °C (707 °F) at a pressure of 218 atmospheres.

However, introducing salinity into the fluid raises the critical point to higher temperatures and pressures. The critical point of seawater (3.2 wt. % NaCl) is 407 °C (765 °F) and 298.5 bars, [8] corresponding to a depth of

2,960 m (9,710 ft) below sea level. Accordingly, if a hydrothermal fluid with a salinity of 3.2 wt. % NaCl vents above 407 °C (765 °F) and 298.5 bars, it is supercritical. Furthermore, the salinity of vent fluids have been shown to vary widely due to phase separation in the crust. [9] The critical point for lower salinity fluids is at lower temperature and pressure conditions than that for seawater, but higher than that for pure water. For example, a vent fluid with a 2.24 wt. % NaCl salinity has the critical point at 400 °C (752 °F) and 280.5 bars. Thus, water emerging from the hottest parts of some hydrothermal vents can be a supercritical fluid, possessing physical properties between those of a gas and those of a liquid. [6] [7]

Examples of supercritical venting are found at several sites. Sister Peak (Comfortless Cove Hydrothermal Field, 4°48′S 12°22′W  /  4.800°S 12.367°W  / -4.800 -12.367 , depth 2,996 m or 9,829 ft) vents low salinity phase-separated, vapor-type fluids. Sustained venting was not found to be supercritical but a brief injection of 464 °C (867 °F) was well above supercritical conditions. A nearby site, Turtle Pits, was found to vent low salinity fluid at 407 °C (765 °F), which is above the critical point of the fluid at that salinity. A vent site in the Cayman Trough named Beebe, which is the world's deepest known hydrothermal site at

5,000 m (16,000 ft) below sea level, has shown sustained supercritical venting at 401 °C (754 °F) and 2.3 wt% NaCl. [10]

Although supercritical conditions have been observed at several sites, it is not yet known what significance, if any, supercritical venting has in terms of hydrothermal circulation, mineral deposit formation, geochemical fluxes or biological activity.

The initial stages of a vent chimney begin with the deposition of the mineral anhydrite. Sulfides of copper, iron, and zinc then precipitate in the chimney gaps, making it less porous over the course of time. Vent growths on the order of 30 cm (1 ft) per day have been recorded. [11] An April 2007 exploration of the deep-sea vents off the coast of Fiji found those vents to be a significant source of dissolved iron (see iron cycle). [12]

Some hydrothermal vents form roughly cylindrical chimney structures. These form from minerals that are dissolved in the vent fluid. When the superheated water contacts the near-freezing sea water, the minerals precipitate out to form particles which add to the height of the stacks. Some of these chimney structures can reach heights of 60 m. [13] An example of such a towering vent was "Godzilla", a structure on the Pacific Ocean deep seafloor near Oregon that rose to 40 m before it fell over in 1996. [14]

A black smoker or deep sea vent is a type of hydrothermal vent found on the seabed, typically in the bathyal zone (with largest frequency in depths from 2500 m to 3000 m), but also in lesser depths as well as deeper in the abyssal zone. [1] They appear as black, chimney-like structures that emit a cloud of black material. Black smokers typically emit particles with high levels of sulfur-bearing minerals, or sulfides. Black smokers are formed in fields hundreds of meters wide when superheated water from below Earth's crust comes through the ocean floor (water may attain temperatures above 400 °C). [1] This water is rich in dissolved minerals from the crust, most notably sulfides. When it comes in contact with cold ocean water, many minerals precipitate, forming a black, chimney-like structure around each vent. The deposited metal sulfides can become massive sulfide ore deposits in time. Some black smokers on the Azores portion of the Mid Atlantic Ridge are extremely rich in metal content, such as Rainbow with 24,000 μM concentrations of iron. [15]

Black smokers were first discovered in 1979 on the East Pacific Rise by scientists from Scripps Institution of Oceanography during the RISE Project. [16] They were observed using the deep submergence vehicle ALVIN from the Woods Hole Oceanographic Institution. Now, black smokers are known to exist in the Atlantic and Pacific Oceans, at an average depth of 2100 metres. The most northerly black smokers are a cluster of five named Loki's Castle, [17] discovered in 2008 by scientists from the University of Bergen at 73°N, on the Mid-Atlantic Ridge between Greenland and Norway. These black smokers are of interest as they are in a more stable area of the Earth's crust, where tectonic forces are less and consequently fields of hydrothermal vents are less common. [18] The world's deepest known black smokers are located in the Cayman Trough, 5,000 m (3.1 miles) below the ocean's surface. [19]

White smoker vents emit lighter-hued minerals, such as those containing barium, calcium and silicon. These vents also tend to have lower-temperature plumes probably because they are generally distant from their heat source. [1]

Black and white smokers may coexist in the same hydrothermal field, but they generally represent proximal (close) and distal (distant) vents to the main upflow zone, respectively. However, white smokers correspond mostly to waning stages of such hydrothermal fields, as magmatic heat sources become progressively more distant from the source (due to magma crystallization) and hydrothermal fluids become dominated by seawater instead of magmatic water. Mineralizing fluids from this type of vent are rich in calcium and they form dominantly sulfate-rich (i.e., barite and anhydrite) and carbonate deposits. [1]

Life has traditionally been seen as driven by energy from the sun, but deep-sea organisms have no access to sunlight, so biological communities around hydrothermal vents must depend on nutrients found in the dusty chemical deposits and hydrothermal fluids in which they live. Previously, Benthic oceanographers assumed that vent organisms were dependent on marine snow, as deep-sea organisms are. This would leave them dependent on plant life and thus the sun. Some hydrothermal vent organisms do consume this "rain", but with only such a system, life forms would be sparse. Compared to the surrounding sea floor, however, hydrothermal vent zones have a density of organisms 10,000 to 100,000 times greater.

The hydrothermal vents are recognized as a type of chemosynthetic based ecosystems (CBE) where primary productivity is fuelled by chemical compounds as energy sources instead of light (chemoautotrophy). [20] Hydrothermal vent communities are able to sustain such vast amounts of life because vent organisms depend on chemosynthetic bacteria for food. The water from the hydrothermal vent is rich in dissolved minerals and supports a large population of chemoautotrophic bacteria. These bacteria use sulfur compounds, particularly hydrogen sulfide, a chemical highly toxic to most known organisms, to produce organic material through the process of chemosynthesis.

Biological communities Edit

The ecosystem so formed is reliant upon the continued existence of the hydrothermal vent field as the primary source of energy, which differs from most surface life on Earth, which is based on solar energy. However, although it is often said that these communities exist independently of the sun, some of the organisms are actually dependent upon oxygen produced by photosynthetic organisms, while others are anaerobic.

The chemosynthetic bacteria grow into a thick mat which attracts other organisms, such as amphipods and copepods, which graze upon the bacteria directly. Larger organisms, such as snails, shrimp, crabs, tube worms, fish (especially eelpout, cutthroat eel, ophidiiforms and Symphurus thermophilus), and octopuses (notably Vulcanoctopus hydrothermalis), form a food chain of predator and prey relationships above the primary consumers. The main families of organisms found around seafloor vents are annelids, pogonophorans, gastropods, and crustaceans, with large bivalves, vestimentiferan worms, and "eyeless" shrimp making up the bulk of nonmicrobial organisms.

Siboglinid tube worms, which may grow to over 2 m (6.6 ft) tall in the largest species, often form an important part of the community around a hydrothermal vent. They have no mouth or digestive tract, and like parasitic worms, absorb nutrients produced by the bacteria in their tissues. About 285 billion bacteria are found per ounce of tubeworm tissue. Tubeworms have red plumes which contain hemoglobin. Hemoglobin combines with hydrogen sulfide and transfers it to the bacteria living inside the worm. In return, the bacteria nourish the worm with carbon compounds. Two of the species that inhabit a hydrothermal vent are Tevnia jerichonana, and Riftia pachyptila. One discovered community, dubbed "Eel City", consists predominantly of the eel Dysommina rugosa. Though eels are not uncommon, invertebrates typically dominate hydrothermal vents. Eel City is located near Nafanua volcanic cone, American Samoa. [21]

In 1993, already more than 100 gastropod species were known to occur in hydrothermal vents. [22] Over 300 new species have been discovered at hydrothermal vents, [23] many of them "sister species" to others found in geographically separated vent areas. It has been proposed that before the North American plate overrode the mid-ocean ridge, there was a single biogeographic vent region found in the eastern Pacific. [24] The subsequent barrier to travel began the evolutionary divergence of species in different locations. The examples of convergent evolution seen between distinct hydrothermal vents is seen as major support for the theory of natural selection and of evolution as a whole.

Although life is very sparse at these depths, black smokers are the centers of entire ecosystems. Sunlight is nonexistent, so many organisms – such as archaea and extremophiles– convert the heat, methane, and sulfur compounds provided by black smokers into energy through a process called chemosynthesis. More complex life forms, such as clams and tubeworms, feed on these organisms. The organisms at the base of the food chain also deposit minerals into the base of the black smoker, therefore completing the life cycle.

A species of phototrophic bacterium has been found living near a black smoker off the coast of Mexico at a depth of 2,500 m (8,200 ft). No sunlight penetrates that far into the waters. Instead, the bacteria, part of the Chlorobiaceae family, use the faint glow from the black smoker for photosynthesis. This is the first organism discovered in nature to exclusively use a light other than sunlight for photosynthesis. [25]

New and unusual species are constantly being discovered in the neighborhood of black smokers. The Pompeii worm Alvinella pompejana, which is capable of withstanding temperatures up to 80 °C (176 °F), was found in the 1980s, and a scaly-foot gastropod Chrysomallon squamiferum in 2001 during an expedition to the Indian Ocean's Kairei hydrothermal vent field. The latter uses iron sulfides (pyrite and greigite) for the structure of its dermal sclerites (hardened body parts), instead of calcium carbonate. The extreme pressure of 2500 m of water (approximately 25 megapascals or 250 atmospheres) is thought to play a role in stabilizing iron sulfide for biological purposes. This armor plating probably serves as a defense against the venomous radula (teeth) of predatory snails in that community.

In March 2017, researchers reported evidence of possibly the oldest forms of life on Earth. Putative fossilized microorganisms were discovered in hydrothermal vent precipitates in the Nuvvuagittuq Belt of Quebec, Canada, that may have lived as early as 4.280 billion years ago, not long after the oceans formed 4.4 billion years ago, and not long after the formation of the Earth 4.54 billion years ago. [26] [27] [28]

Animal-bacterial symbiosis Edit

Hydrothermal vent ecosystems have enormous biomass and productivity, but this rests on the symbiotic relationships that have evolved at vents. Deep-sea hydrothermal vent ecosystems differ from their shallow-water and terrestrial hydrothermal counterparts due to the symbiosis that occurs between macroinvertebrate hosts and chemoautotrophic microbial symbionts in the former. [29] Since sunlight does not reach deep-sea hydrothermal vents, organisms in deep-sea hydrothermal vents cannot obtain energy from the sun to perform photosynthesis. Instead, the microbial life found at hydrothermal vents is chemosynthetic they fix carbon by using energy from chemicals such as sulfide, as opposed to light energy from the sun. In other words, the symbiont converts inorganic molecules (H2S, CO2, O) to organic molecules that the host then uses as nutrition. However, sulfide is an extremely toxic substance to most life on Earth. For this reason, scientists were astounded when they first found hydrothermal vents teeming with life in 1977. What was discovered was the ubiquitous symbiosis of chemoautotrophs living in (endosymbiosis) the vent animals' gills the reason why multicellular life is capable to survive the toxicity of vent systems. Scientists are therefore now studying how the microbial symbionts aid in sulfide detoxification (therefore allowing the host to survive the otherwise toxic conditions). Work on microbiome function shows that host-associated microbiomes are also important in host development, nutrition, defense against predators, and detoxification. In return, the host provides the symbiont with chemicals required for chemosynthesis, such as carbon, sulfide, and oxygen. [ citation needed ]

In the early stages of studying life at hydrothermal vents, there were differing theories regarding the mechanisms by which multicellular organisms were able to acquire nutrients from these environments, and how they were able to survive in such extreme conditions. In 1977, it was hypothesized that the chemoautotrophic bacteria at hydrothermal vents might be responsible for contributing to the diet of suspension-feeding bivalves. [30]

Finally, in 1981, it was understood that giant tubeworm nutrition acquisition occurred as a result of chemoautotrophic bacterial endosymbionts. [31] [32] [33] As scientists continued to study life at hydrothermal vents, it was understood that symbiotic relationships between chemoautotrophs and macrofauna invertebrate species was ubiquitous. For instance, in 1983, clam gill tissue was confirmed to contain bacterial endosymbionts [34] in 1984 vent bathymodiolid mussels and vesicomyid clams were also found to carry endosymbionts. [35] [36]

However, the mechanisms by which organisms acquire their symbionts differ, as do the metabolic relationships. For instance, tubeworms have no mouth and no gut, but they do have a "trophosome", which is where they deal with nutrition and where their endosymbionts are found. They also have a bright red plume, which they use to uptake compounds such as O, H2S, and CO2, which feed the endosymbionts in their trophosome. Remarkably, the tubeworms hemoglobin (which incidentally is the reason for the bright red color of the plume) is capable of carrying oxygen without interference or inhibition from sulfide, despite the fact that oxygen and sulfide are typically very reactive. In 2005, it was discovered that this is possible due to zinc ions that bind the hydrogen sulfide in the tubeworms hemoglobin, therefore preventing the sulfide from reacting with the oxygen. It also reduces the tubeworms tissue from exposure to the sulfide and provides the bacteria with the sulfide to perform chemoautotrophy. [37] It has also been discovered that tubeworms can metabolize CO2 in two different ways, and can alternate between the two as needed as environmental conditions change. [38]

In 1988, research confirmed thiotrophic (sulfide-oxidizing) bacteria in Alvinochonca hessleri, a large vent mollusk. [39] In order to circumvent the toxicity of sulfide, mussels first convert it to thiosulfate before carrying it over to the symbionts. [40] In the case of motile organisms such as alvinocarid shrimp, they must track oxic (oxygen-rich) / anoxic (oxygen-poor) environments as they fluctuate in the environment. [ citation needed ]

Organisms living at the edge of hydrothermal vent fields, such as pectinid scallops, also carry endosymbionts in their gills, and as a result their bacterial density is low relative to organisms living nearer to the vent. However, the scallop's dependence on the microbial endosymbiont for obtaining their nutrition is therefore also lessened. [ citation needed ]

Furthermore, not all host animals have endosymbionts some have episymbionts—symbionts living on the animal as opposed to inside the animal. Shrimp found at vents in the Mid-Atlantic Ridge were once thought of as an exception to the necessity of symbiosis for macroinvertebrate survival at vents. That changed in 1988 when they were discovered to carry episymbionts. [41] Since then, other organisms at vents have been found to carry episymbionts as well, [42] such as Lepetodrilis fucensis. [43]

Furthermore, while some symbionts reduce sulfur compounds, others are known as "methanotrophs" and reduce carbon compounds, namely methane. Bathmodiolid mussels are an example of a host that contains methanotrophic endosymbionts however, the latter mostly occur in cold seeps as opposed to hydrothermal vents. [ citation needed ]

While chemosynthesis occurring at the deep ocean allows organisms to live without sunlight in the immediate sense, they technically still rely on the sun for survival, since oxygen in the ocean is a byproduct of photosynthesis. However, if the sun were to suddenly disappear and photosynthesis ceased to occur on our planet, life at the deep-sea hydrothermal vents could continue for millennia (until the oxygen was depleted). [ citation needed ]

Theory of hydrothermal origin of life Edit

The chemical and thermal dynamics in hydrothermal vents makes such environments highly suitable thermodynamically for chemical evolution processes to take place. Therefore, thermal energy flux is a permanent agent and is hypothesized to have contributed to the evolution of the planet, including prebiotic chemistry. [1]

Günter Wächtershäuser proposed the iron-sulfur world theory and suggested that life might have originated at hydrothermal vents. Wächtershäuser proposed that an early form of metabolism predated genetics. By metabolism he meant a cycle of chemical reactions that release energy in a form that can be harnessed by other processes. [44]

It has been proposed that amino acid synthesis could have occurred deep in the Earth's crust and that these amino acids were subsequently shot up along with hydrothermal fluids into cooler waters, where lower temperatures and the presence of clay minerals would have fostered the formation of peptides and protocells. [45] This is an attractive hypothesis because of the abundance of CH4 (methane) and NH3 (ammonia) present in hydrothermal vent regions, a condition that was not provided by the Earth's primitive atmosphere. A major limitation to this hypothesis is the lack of stability of organic molecules at high temperatures, but some have suggested that life would have originated outside of the zones of highest temperature. [46] There are numerous species of extremophiles and other organisms currently living immediately around deep-sea vents, suggesting that this is indeed a possible scenario.

Experimental research and computer modeling indicate that the surfaces of mineral particles inside hydrothermal vents have similar catalytic properties to enzymes and are able to create simple organic molecules, such as methanol (CH3OH) and formic acid (HCO2H), out of the dissolved CO2 in the water. [47] [48] [49]

It is thought that alkaline hydrothermal vents (white smokers) might be more suitable for emerging life than black smokers due to their pH conditions. [50] [51]

The Deep Hot Biosphere Edit

At the beginning of his 1992 paper The Deep Hot Biosphere, Thomas Gold referred to ocean vents in support of his theory that the lower levels of the earth are rich in living biological material that finds its way to the surface. [52] He further expanded his ideas in the book The Deep Hot Biosphere. [53]

An article on abiogenic hydrocarbon production in the February 2008 issue of Science journal used data from experiments at the Lost City hydrothermal field to report how the abiotic synthesis of low molecular mass hydrocarbons from mantle derived carbon dioxide may occur in the presence of ultramafic rocks, water, and moderate amounts of heat. [54]


Types of Ecosystem

Ecosystem types abound however, the most basic categorization involves three habitats: terrestrial, marine, and aquatic. Naturally, these groups can be split into thousands of smaller systems, each one offering a different mix of climate, habitat and life forms.

Terrestrial Ecosystems – Global Land-Based Habitats

At approximately 57 268 900 square miles, the terrestrial ecosystem covers just 29% of the globe. As these habitats are varied, terrestrial ecosystems are further broken down into six types.

The deciduous forest ecosystem is found in temperate regions and experiences temperature and precipitation fluctuations according to four seasons. Current conservation goals include reintroducing apex predators after the culling practices of previous centuries, and providing an environment full with mature trees to make up for unregulated deforestation.

Desert ecosystems can be hot and dry, semi-arid, coastal or cold. The feature that links these is a lack of water and the absence of a soil layer in which larger vegetation such as shrubs and trees can thrive. While indigenous life has adapted to the absence of water, a desert is still unable to support the populations of a wetter habitat. Substantially sized herbivores are unable to survive in a desert environment in large numbers, and this in turn limits the numbers of larger omnivores and carnivores.

Grasslands are also known as prairies, pampas, savanna or steppe. They can be tropical or temperate, and are a link between desert and forest. They rarely receive enough rain to support trees, but possess enough soil nutrients to feed large, grassy expanses. This provides considerable energy for primary consumers. With a large population of producers, a grassland ecosystem can similarly support large herds of herbivores, which in turn feed consumers higher up in the food chain hierarchy.

The taiga is a region of subarctic forest south of the Arctic Circle. It has layers of permafrost or rock under shallow soil, which make the soil marshy. The taiga supports huge numbers of conifers – slow growing, cold-resistant trees. Other plant life is small and includes lichen, marshland plants and small shrubs. The map below shows how this ecosystem is distributed across the globe.

Tropical rainforests are probably the most quoted ecosystems in the field of environmental conservation. Located around the Equator, constant rainfall and warmth together with a lack of seasons provide a stable climate, yet cloud and the tree canopy make the rainforest floor a dark place. Soil is leached of nutrients through constant precipitation. Plant life has adapted and is abundant, making the tropical rainforest ecosystem the terrestrial ecosystem with the most biodiversity.

Tundra, the last of the six terrestrial biomes, is the treeless environment of the Arctic Circle. Climate change is rapidly changing this ecosystem, as warmer weather brings non-indigenous predators in, where they compete for limited prey. Certain shrubs are taking root as the Artic permafrost layer melts. These compete with lichen – the primary food source of caribou.

Marine Ecosystems – Biodiversity in Oceans, Seas and Glaciers

Marine and aquatic ecosystems cover 139 668 500 square miles 97% of this is salt water, making marine ecosystems the largest biome category.

Large marine ecosystems (LMEs) are particularly difficult to observe and control, as different salt water habitats have complex chemical compositions that vary from coast to coast and from shallow to deep. These compositions are forever shifting due to tides and currents. Pollutants and organisms travel on courses which, although predictable, are continuously in motion. The sheer volume of water a large marine ecosystem covers is immense. The map below shows the population trends of native and invasive species of jellyfish and their populations. This study looks at the trends of jellyfish behavior in an LME. To predict this trend on a global scale is possible, but the potential and actual variables are countless.

Marine or ocean ecosystems are grouped into open marine, ocean floor, coral reef, estuary, saltwater wetland estuary, and mangrove systems. These cover marine environments from the surfaces and floors of the deepest oceans to partially terrestrial, tidal swamps.

Aquatic Ecosystems – Freshwater Locations: Lakes, pools and rivers

Freshwater ecosystems cover approximately 3% of the planet’s surface. Aquatic ecosystems also include estuaries before freshwater meets salt, wetlands, ponds (natural or artificial), lakes, and rivers.

As fresh water is essential for all life, aquatic biomes are extremely important. Yet they are very small in comparison to other habitats, and have been used as dumping grounds for centuries. National Geographic reports that freshwater species are four to six times more at risk of becoming extinct than terrestrial or marine species. Freshwater biomes and coastal marine systems are also at high risk of eutrophication, a natural process which requires centuries to develop. Eutrophication is caused by increased levels of sediments which in turn increase levels of nutrients and encourage excessive plant growth. When vegetation dies off, after depleting the additional nutrients or becoming victims of their own success, their decomposition leads to dead zones, or hypoxic zones.

Microbiomes – Supporting the Biodiversity of Living Organisms

Any anatomical system contains microbiota – mutualistic, commensalistic, pathogenic or parasitic bacteria, fungi, archaea and viruses.

Health publications now report a relationship between gut biodiversity and the health of other anatomical and physiological systems, such as mood, hormonal production and resistance. This may be likened to the effect of reducing biodiversity in aquatic ecosystems, and the effect this will have on populations at distant locations. For example, research is looking into the prevalence of chronic inflammatory diseases as microbial diversity in the intestine decreases.

The microbiome may not be an ecological ecosystem, but it is a complete ecosystem of living and non-living components in a habitat where interactions take place, and which has its own climate.


Contents

The largest single-stem tree by wood volume and mass is the giant sequoia (Sequoiadendron giganteum), native to Sierra Nevada and California it typically grows to a height of 70–85 m (230–280 ft) and 5–7 m (16–23 ft) in diameter.

The largest organism in the world, according to mass, is the aspen tree whose colonies of clones can grow up to 8 kilometres (5 mi) long. The largest such colony is Pando, in the Fishlake National Forest in Utah.

Another form of flowering plant that rivals Pando as the largest organism on earth in breadth, if not mass, is the giant marine plant, Posidonia oceanica, discovered in the Mediterranean near the Balearic Islands, Spain. Its length is about 8 km (5 mi). It may also be the oldest living organism in the world, with an estimated age of 100,000 years. [7]

The largest individual flower in the world is Rafflesia arnoldii, while the flowering plant with the largest unbranched inflorescence in the world is Amorphophallus titanum, both are native to Sumatra island of indonesia.

Green algae Edit

Green algae are photosynthetic unicellular and multicellular protists that are related to land plants. The thallus of the unicellular mermaid's wineglass, Acetabularia, can grow to several inches (perhaps 0.1 to 0.2 m) in length. The fronds of the similarly unicellular, and invasive Caulerpa taxifolia can grow up to a foot (0.3 m) long. [ citation needed ]

A member of the infraorder Cetacea, the blue whale (Balaenoptera musculus), is thought to be the largest animal ever to have lived. The maximum recorded weight was 190 tonnes for a specimen measuring 27.6 metres (91 ft), whereas longer ones, up to 33.6 metres (110 ft), have been recorded but not weighed. [8] [9] [10] It is estimated however that this individual could have a mass of 250 tonnes. [11] [12] The title of the longest non-colonial animal is probably owned by Lion's mane jellyfish (36.6m / 120 ft). [13]

The African bush elephant (Loxodonta africana), of the order Proboscidea, is the largest living land animal. A native of various open habitats in sub-Saharan Africa, this elephant is commonly born weighing about 100 kilograms (220 lb). [14] The largest elephant ever recorded was shot in Angola in 1974. It was a male measuring 10.67 metres (35.0 ft) from trunk to tail and 4.17 metres (13.7 ft) lying on its side in a projected line from the highest point of the shoulder to the base of the forefoot, indicating a standing shoulder height of 3.96 metres (13.0 ft). This male had a computed weight of 12.25 tonnes. [8]

Heaviest living animals Edit

The heaviest living animals are all cetaceans, and thus also the largest living mammals. Since no scale can accommodate the whole body of a large whale, most whales have been weighed by parts.

Rank Animal Average mass
[tonnes]
Maximum mass
[tonnes]
Average total length
[m (ft)]
1 Blue whale 110 [15] 190 [8] 24 (79) [16]
2 North Pacific right whale 60 [17] 120 [8] 15.5 (51) [15]
3 Southern right whale 58 [15] 110 [18] 15.25 (50) [15]
4 Fin whale 57 [15] 120 [18] 19.5 (64) [15]
5 Bowhead whale 54.5 [15] [19] 120 [8] 15 (49) [15]
6 North Atlantic right whale 54 [15] [20] 110 [18] [21] 15 (49) [15] [21]
7 Sperm whale 31.25 [15] [22] 57 [8] 13.25 (43.5) [15] [22]
8 Humpback whale 29 [15] [23] 48 [24] 13.5 (44) [15]
9 Sei whale 22.5 [15] 45 [25] 14.8 (49) [15]
10 Gray whale 19.5 [15] 45 [26] 13.5 (44) [15]

Heaviest terrestrial animals Edit

The following is a list of the heaviest wild land animals, which are all mammals. The African elephant is now listed as two species, the African bush elephant and the African forest elephant, as they are now generally considered to be two separate species. [27]

Rank Animal Average mass
[tonnes]
Maximum mass
[tonnes]
Average total length
[m (ft)]
1 African bush elephant 4.9 [28] [29] 10.4 [30] 6 (19.7) [31]
2 Asian elephant 4.15 [8] [32] 8.15 [8] 6.8 (22.3) [32]
3 African forest elephant 2.7 [33] 6.0 [33] 6.2 (20.3) [34]
4 White rhinoceros [ dubious – discuss ] 2 [35] [36] 4.5 [37] 4.4 (14.4) [38]
5 Indian rhinoceros 1.9 [39] [40] 4.0 [41] 4.2 (13.8) [42]
6 Hippopotamus 1.8 [43] [44] 4.5 [45] 5.05 (16.5) [46]
7 Javan rhinoceros 1.75 [47] [48] 2.3 [49] 3.8 (12.5) [50]
8 Black rhinoceros 1.1 [51] 2.9 [52] 4 (13.1) [53]
9 Giraffe 1.0 [8] 2 [54] 5.15 (16.9) [55]
10 Gaur 0.95 [56] 1.5 [56] 3.8 (12.5) [57]

Tunicates (Tunicata) Edit

The largest tunicates are Synoicum pulmonaria, found at depths of 20 and 40 metres (66 and 131 ft), and are up to 14 centimetres (6 in) in diameter. It is also present in the northwestern Atlantic Ocean, around the coasts of Greenland and Newfoundland, but is less common here than in the east, and occurs only at depths between 10 and 13 metres (33 and 43 ft). [58]

Entergonas (Enterogona) The largest entergonas Synoicum pulmonaria it is usually found at depths between about 20 and 40 metres (66 and 131 ft) and can grow to over a metre (yard) in length. It is also present in the northwestern Atlantic Ocean, around the coasts of Greenland and Newfoundland, but is less common here than in the east, and occurs only at depths between 10 and 13 metres (33 and 43 ft). [58] Pleurogonas (Pleurogona) The largest pleurogonas: Pyura pachydermatina . [59] In colour it is off-white or a garish shade of reddish-purple. The stalk is two thirds to three quarters the length of the whole animal which helps distinguish it from certain invasive tunicates not native to New Zealand such as Styela clava and Pyura stolonifera. [60] It is one of the largest species of tunicates and can grow to over a metre (yard) in length. [61] Aspiraculates (Aspiraculata) The largest aspiraculates: Oligotrema large and surrounded by six large lobes the cloacal syphon is small. They live exclusively in deep water and range in size from less than one inch (2 cm) to 2.4 inches (6 cm).

Thaliacea Edit

The largest thaliacean, Pyrosoma atlanticum, is cylindrical and can grow up to 60 cm (2 ft) long and 4–6 cm wide. The constituent zooids form a rigid tube, which may be pale pink, yellowish, or bluish. One end of the tube is narrower and is closed, while the other is open and has a strong diaphragm. The outer surface or test is gelatinised and dimpled with backward-pointing, blunt processes. The individual zooids are up to 8.5 mm (0.33 in) long and have a broad, rounded branchial sac with gill slits. Along the side of the branchial sac runs the endostyle, which produces mucus filters. Water is moved through the gill slits into the centre of the cylinder by cilia pulsating rhythmically. Plankton and other food particles are caught in mucus filters in the processes as the colony is propelled through the water. P. atlanticum is bioluminescent and can generate a brilliant blue-green light when stimulated. [62] [63]

Doliolida (Doliolida) The largest doliolida: Doliolida [64] The doliolid body is small, typically 1–2 cm long, and barrel-shaped it features two wide siphons, one at the front and the other at the back end, and eight or nine circular muscle strands reminiscent of barrel bands. Like all tunicates, they are filter feeders. They are free-floating the same forced flow of water through their bodies with which they gather plankton is used for propulsion - not unlike a tiny ramjet engine. Doliolids are capable of quick movement. They have a complicated lifecycle consisting of sexual and asexual generations. They are nearly exclusively tropical animals, although a few species are found as far north as northern California. [ citation needed ] Salps (Salpida) The largest salps: Cyclosalpa bakeri15cm (6ins) long. There are openings at the anterior and posterior ends of the cylinder which can be opened or closed as needed. The bodies have seven transverse bands of muscle interspersed by white, translucent patches. A stolon grows from near the endostyle (an elongated glandular structure producing mucus for trapping food particles). The stolon is a ribbon-like organ on which a batch of aggregate forms of the animal are produced by budding. The aggregate is the second, colonial form of the salp and is also gelatinous, transparent and flabby. It takes the shape of a radial whorl of individuals up to about 20cm (4in) in diameter. It is formed of approximately 12 zooids linked side by side in a shape that resembles a crown. [62] [65] are largest thetyses: Thetys vagina Individuals can reach up to 30 cm (12 in) long. [ citation needed ] Larvaceans (Larvacea) The largest larvaceans: Appendicularia 1 cm (0.39 in) in body length (excluding the tail). [ citation needed ]

Cephalochordates (Leptocardii) Edit

The largest lancelets: European lancelet (Branchiostoma lanceolatum) "primitive fish". It can grow up to 6 cm (2.5 in) long. [66]

Vertebrates Edit

Mammals (Mammalia) Edit

The largest land mammal extant today is the African bush elephant. The largest extinct land mammal known was long considered to be Paraceratherium orgosensis, a rhinoceros relative thought to have stood up to 4.8 m (15.7 ft) tall, measured over 7.4 m (24.3 ft) long and may have weighed about 17 tonnes. [67] [68] In 2015, a study suggested that one example of the proboscidean Palaeoloxodon namadicus may have been the largest land mammal ever, based on extensive research of fragmentary leg bone fossils from one individual, with a maximum estimated size of 22 tonnes. [69] [67]

Stem-mammals (Synapsida) Edit

The Triassic period Lisowicia bojani, from what is now southern Poland, probably was the largest of all non-mammalian synapsids (most of which became extinct 250 million years ago), at 4.5 m (15 ft) and 9 tonnes. [70] However, one study suggested a more conservative weight of 4.87 tonnes to 7.02 tonnes for the adult taxon, with an average body mass of 5.88 tonnes. [71] The largest carnivorous synapsid was Anteosaurus from what is now South Africa during Middle Permian epoch. Anteosaurus was 5–6 m (16–20 ft) long, and weighed about 500–600 kg (1,100–1,300 lb). [72]

Pelycosauria The largest pelycosaur was Cotylorhynchus, measuring 6 m (20 ft) and weighing 2 tonnes, [73] and the largest predatory pelycosaur was Dimetrodon grandis from what is now North America, with a length of 3.1 m (10 ft) and weight of 250 kg (550 lb). [74] Therapsida The plant-eating dicynodont Lisowicia bojani is the largest-known of all non-mammal synapsids, at 4.5 m (15 ft) and 9,000 kg (20,000 lb). [70] [75] [76] The largest carnivorous therapsid was the aforementioned Anteosaurus. [ citation needed ]

Reptiles (Reptilia) Edit

The largest living reptile, a representative of the order Crocodilia, is the saltwater crocodile (Crocodylus porosus) of Southern Asia and Australia, with adult males being typically 3.9–5.5 m (13–18 ft) long. The largest confirmed saltwater crocodile on record was 6.32 m (20.7 ft) long, and weighed about 1,360 kg (3,000 lb). [8] Unconfirmed reports of much larger crocodiles exist, but examinations of incomplete remains have never suggested a length greater than 7 m (23 ft). [77] Also, a living specimen estimated at 7 m (23 ft) and 2,000 kg (4,400 lb) has been accepted by the Guinness Book of World Records. [78] However, due to the difficulty of trapping and measuring a very large living crocodile, the accuracy of these dimensions has yet to be verified. A specimen named Lolong caught alive in the Philippines in 2011 (died February 2013) was found to have measured 6.17 m (20.2 ft) in length. [79] [80] [81] [82] [83]

The Komodo dragon (Varanus komodoensis), also known as the "Komodo monitor", is a large species of lizard found in the Indonesian islands of Komodo, Rinca, Flores, Gili Motang, Nusa kode and Padar. A member of the monitor lizard family (Varanidae), it is the largest living species of lizard, growing to a maximum length of 3 metres (9.8 feet) in rare cases and weighing up to approximately 70 kilograms (150 pounds). [ citation needed ]

Heaviest living reptiles Edit

The following is a list of the heaviest living reptile species ranked by average weight, which is dominated by the crocodilians. Unlike mammals, birds, or fish, the mass of large reptiles is frequently poorly documented and many are subject to conjecture and estimation. [8]

Rank Animal Average mass
[kg (lb)]
Maximum mass
[kg (lb)]
Average total length
[m (ft)]
1 Saltwater crocodile 450 (990) [84] [85] 2,000 (4,400) [86] [87] 4.5 (14.8) [84] [88]
2 Nile crocodile 410 (900) [89] 1,090 (2,400) [8] 4.2 (13.8) [89]
3 Orinoco crocodile 380 (840) [ citation needed ] 1,100 (2,400) [ citation needed ] 4.1 (13.5) [90] [91]
4 Leatherback sea turtle 364 (800) [92] [93] 932 (2,050) [8] 2.0 (6.6) [8]
5 Black caiman 350 (770) [ citation needed ] 1,100 (2,400) [ citation needed ] 3.9 (12.8) [94] [95] [96] [97]
6 American crocodile 335 (739) [98] 1,000 (2,200) [99] 4.0 (13.1) [100] [101]
7 Gharial 250 (550) [102] 977 (2,150) [103] 4.5 (14.8) [102]
8 American alligator 240 (530) [104] [105] 1,000 (2,200) [8] 3.4 (11.2) [105]
9 Mugger crocodile 225 (495) [104] 700 (1,500) [106] 3.3 (10.8) [105]
10 False gharial 210 (460) [107] 500 (1,100) [ citation needed ] 4.0 (13.1) [108]
11 Aldabra giant tortoise 205 (450) [109] 360 (790) [8] 1.4 (4.6) [110]
12 Loggerhead sea turtle 200 (441) [ citation needed ] 545 (1202) [ citation needed ] 0.95 (3.2) [110]
13 Green sea turtle 190 (418.9) [111] 395 (870.8) [89] 1.12 (3.67) [89]
14 Slender-snouted crocodile 180 (400) [112] [113] 325 (720) [112] 3.3 (10.8) [112]
15 Galapagos tortoise 175 (390) [114] 417 (919) [115] 1.5 (4.9) [116]

Dinosaurs (Dinosauria) Edit

Dinosaurs are now extinct, except for birds, which are theropods.

Sauropods (Sauropoda) The largest dinosaurs, and the largest animals to ever live on land, were the plant-eating, long-necked Sauropoda. The tallest and heaviest sauropod known from a complete skeleton is a specimen of an immature Giraffatitan discovered in Tanzania between 1907 and 1912, now mounted in the Museum für Naturkunde of Berlin. It is 12–13.27 m (39.4–43.5 ft) tall and weighed 23.3–39.5 tonnes. [117] [118] [119] [120] [121] [122] The longest is a 25 m (82 ft) long specimen of Diplodocus discovered in Wyoming, and mounted in Pittsburgh's Carnegie Natural History Museum in 1907. A Patagotitan specimen found in Argentina in 2014 is estimated to have been 37–40 m (121–131 ft) long and 20 m (66 ft) tall, with a weight of 69-77 tonnes. [123] [124] There were larger sauropods, but they are known only from a few bones. The current record-holders include Argentinosaurus, which may have weighed 100 tonnes Supersaurus which might have reached 34 m (112 ft) in length and Sauroposeidon which might have been 18 m (59 ft) tall. Two other such sauropods include Bruhathkayosaurus and Maraapunisaurus. Both are known only from fragments. Bruhathkayosaurus might have been between 40–44 m (131–144 ft) in length and 175–220 tonnes in weight according to some estimates. [125] Maraapunisaurus might have been approximately 30.3-32 m long. [126] Theropods (Theropoda) The largest theropod known from a nearly complete skeleton is the most complete Tyrannosaurus rex specimen, nicknamed "Sue", which was discovered in South Dakota in 1990 and now mounted in the Field Museum of Chicago at a total length of 12.3 m (40 ft). Body mass estimates have reached over 9,500 kg, [127] though other figures, such as Hartman's 2013 estimate of 8,400 kg, [128] have been lower. Another giant theropod is Spinosaurus aegyptiacus from the mid-Cretaceous of North Africa. Size estimates have been fluctuating far more over the years, with length estimates ranging from 12.6 to 18 m and mass estimates from 7 to 20.9 t. [129] [130] Recent findings favor a length exceeding 15 m [131] and a body mass of 7.5 tons. [132] Other contenders known from partial skeletons include Giganotosaurus carolinii (est. 12.2–13.2 m and 6-13.8 tonnes) and Carcharodontosaurus saharicus (est. 12-13.3 m and 6.2-15.1 tonnes). [130] [133] [134] [135] [136] [137] The largest extant theropod is the common ostrich (see birds, below). Armored dinosaurs (Thyreophora) The largest thyreophorans were Ankylosaurus and Stegosaurus, from the Late Cretaceous and Late Jurassic periods (respectively) of what is now North America, both measuring up to 9 m (30 ft) in length and estimated to weigh up to 6 tonnes. [138] [139] Ornithopods (Ornithopoda) The largest ornithopods were the hadrosaurids Shantungosaurus, a late Cretaceous dinosaur found in the Shandong Peninsula of China, and Magnapaulia from the late Cretaceous of North America. Both species are known from fragmentary remains but are estimated to have reached over 15 m (49 ft) in length [140] [141] and were likely the heaviest non-sauropod dinosaurs, estimated at over 23 tonnes. [141] Ceratopsians (Ceratopsia) The largest ceratopsians were Triceratops and its ancestor Eotriceratops from the late Cretaceous of North America. Both estimated to have reached about 9 m (30 ft) in length [142] and weighed 12 tonnes. [143] [144]

Birds (Aves) Edit

The largest living bird, a member of the Struthioniformes, is the common ostrich (Struthio camelus), from the plains of Africa. A large male ostrich can reach a height of 2.8 m (9.2 ft) and weigh over 156 kg (344 lb). [145] A mass of 200 kg (440 lb) has been cited for the common ostrich but no wild ostriches of this weight have been verified. [146] Eggs laid by the ostrich can weigh 1.4 kg (3.1 lb) and are the largest eggs in the world today. [ citation needed ]

The largest bird in the fossil record may be the extinct elephant birds (Aepyornithidae) of Madagascar, which were related to the kiwis. Aepyornis exceeded 3 m (9.8 ft) in height and 500 kg (1,100 lb), while Vorombe could reach a similar height and a mass of 732 kg (1,614 lb). [147] The last of the elephant birds became extinct about 300 years ago. Of almost exactly the same upper proportions as the largest elephant birds was Dromornis stirtoni of Australia, part of a 26,000-year-old group called mihirungs of the family Dromornithidae. [148] The largest carnivorous bird was Brontornis, an extinct flightless bird from South America which reached a weight of 350 to 400 kg (770 to 880 lb) and a height of about 2.8 m (9 ft 2 in). [149] The tallest carnivorous bird was Kelenken, which could reach 3 to 3.2 meters in height and 220 to 250 kilograms. The tallest bird ever was the giant moa (Dinornis maximus), part of the moa family of New Zealand that went extinct around 1500 AD. This particular species of moa stood up to 3.7 m (12 ft) tall, [145] but weighed about half as much as a large elephant bird or mihirung due to its comparatively slender frame. [8]

The heaviest bird ever capable of flight was Argentavis magnificens, the largest member of the now extinct family Teratornithidae, found in Miocene-aged fossil beds of Argentina, with a wingspan up to 5.5 m (18 ft), a length of up to 1.25 m (4.1 ft), a height on the ground of up to 1.75 m (5.7 ft) and a body weight of at least 71 kg (157 lb). [8] [150] [151] Pelagornis sandersi is thought to have had an even larger wingspan of about 6.1–7.4 m (20–24 ft), but is only about 22–40 kg (49–88 lb), half the mass of the former. [152] [151]

Heaviest living bird species Edit

The following is a list of the heaviest living bird species based on maximum reported or reliable mass, but average weight is also given for comparison. These species are almost all flightless, which allows for these particular birds to have denser bones and heavier bodies. Flightless birds comprise less than 2% of all living bird species. [ citation needed ]

Rank Animal Binomial Name Average mass
[kg (lb)]
Maximum mass
[kg (lb)]
Average total length
[cm (ft)]
Flighted
1 Ostrich Struthio camelus 104 (230) [153] 156.8 (346) [153] 210 (6.9) [154] No
2 Somali ostrich Struthio molybdophanes 90 (200) [153] 130 (287) [ citation needed ] 200 (6.6) [153] No
3 Southern cassowary Casuarius casuarius 45 (99) [153] 85 (190) [155] 155 (5.1) [153] No
4 Northern cassowary Casuarius unappendiculatus 44 (97) [153] 75 (170) [153] 149 (4.9) [154] No
5 Emu Dromaius novaehollandiae 33 (73) [153] [156] 70 (150) [ citation needed ] 153 (5) [153] No
6 Emperor penguin Aptenodytes forsteri 31.5 (69) [154] [157] 46 (100) [154] 114 (3.7) [154] No
7 Greater rhea Rhea americana 23 (51) [156] 40 (88) [154] 134 (4.4) [153] No
8 Domestic turkey/wild turkey Meleagris gallopavo 13.5 (29.8) [158] 39 (86) [159] 100 - 124.9 (3.3 – 4.1) [ citation needed ] Yes
9 Dwarf cassowary Casuarius bennetti 19.7 (43) [153] 34 (75) [153] 105 (3.4) [ citation needed ] No
10 Lesser rhea Rhea pennata 19.6 (43) [153] 28.6 (63) [153] 96 (3.2) [154] No
11 Mute swan Cygnus olor 11.87 (26.2) 23 (51) 100-130 (3.3 - 4.3) [160] Yes
12 Great bustard Otis tarda 10.6 (23.4) [ citation needed ] 21 (46) [8] 115 (3.8) [ citation needed ] Yes
13 King penguin Aptenodytes patagonicus 13.6 (30) [154] [157] 20 (44) [161] 92 (3) [ citation needed ] No
14 Kori bustard Ardeotis kori 11.4 (25.1) [154] 20 (44.1) [ citation needed ] 150 (5) [154] Yes
15 Trumpeter swan Cygnus buccinator 11.6 (25.1) 17.2 (38) 138 - 165 (4.5 - 5.4) Yes
16 Wandering albatross Diomedea exulans 11.9 (24) 16.1 (38) [162] 107 - 135 (3.5 - 4.4) Yes
17 Whooper swan Cygnus cygnus 11.4 (25) 15.5 (32) 140 - 165 (4.5 - 5.4) Yes
18 Dalmatian Pelican Pelecanus crispus 11.5 (25) 15 (33.1) [ citation needed ] 183 (6) [ citation needed ] Yes
19 Andean condor Vultur gryphus 11.3 (25) [160] 14.9 (33) [160] 100 - 130 (3.3 - 4.3) [160] Yes

Amphibians (Amphibia) Edit

The largest living amphibian is the South China giant salamander (Andrias sligoi). Formerly considered conspecific with the Chinese giant salamander (A. davidianus), the maximum size of this nearly human-sized river-dweller is 64 kg (141 lb) and almost 1.83 m (6.0 ft). [8] Before amniotes became the dominant tetrapods, several giant amphibian proto-tetrapods existed and were certainly the dominant animals in their ecosystems. The largest known was the crocodile-like Prionosuchus, which reached a length of 9 m (30 ft). [163]

Frogs (Anura) The largest member of the largest order of amphibians is the African goliath frog (Conraua goliath). The maximum size this species is verified to attain is a weight of 3.8 kg (8.4 lb) and a snout-to-vent length of 39 cm (15 in). [8] The largest of the toads, the cane toad (Rhinella marina), is also the second largest member of the frog order. This infamous, often invasive species can grow to maximum mass of 2.65 kg (5.8 lb) and measure a maximum of 33 cm (13 in) from snout-to-vent. [8] Rivaling the previous two species, the African bullfrog (Pyxicephalus adspersus) can range up to a weight of 2 kg (4.4 lb) and 25.5 cm (10.0 in) from snout to vent. [164] Another large frog is the largest frog in North America, the American bullfrog, which can reach weights of up to 0.8 kg (1.8 lb) and snout-to-vent-length (SVL) of 20 cm (7.9 in). However, the toad Beelzebufo ampinga, found in fossil from the Cretaceous era in what is now Madagascar, could grow to be 41 cm (16 in) long and weigh up to 4.5 kg (9.9 lb), making it the largest frog ever known. [165] The largest tree frog is the Australasian white-lipped tree frog (Litoria infrafrenata), the females of which can reach a length of 14 cm (5.5 in) from snout to vent and can weigh up to 115 g (4.1 oz). [166] The family Leptodactylidae, one of the most diverse anuran families, also has some very large members. The largest is the Surinam horned frog (Ceratophrys cornuta), which can reach 20 cm (7.9 in) in length from snout to vent and weigh up to 0.48 kg (1.1 lb). [167] While not quite as large as Ceratophrys cornuta, Leptodactylus pentadactylus is often heavier it can reach 18.5 cm (7.3 in) long and weigh 0.60 kilograms (1.3 pounds). The largest dendrobatid is the Colombian golden poison frog (Phyllobates terribilis), which can attain a length of 6 cm (2.4 in) and nearly 28.3 g (1.00 oz). [168] Most frogs are classified under the suborder Neobatrachia, although nearly 200 species are part of the suborder Mesobatrachia, or ancient frogs. The largest of these are the little-known Brachytarsophrys or Karin Hills frogs, of South Asia, which can grow to a maximum snout-to-vent length of 17 cm (6.7 in) and a maximum weight of 0.54 kg (1.2 lb). [169]

Fish Edit

Invertebrates Edit

Sponges (Porifera) Edit

The largest known species of sea sponge is the giant barrel sponge, Xestospongia muta. These massively built sponges can reach 2.4 m (8 ft) in height and can be about the same thickness at the thickest part of the "body". [172] Some of these creatures have been estimated to be over 2,400 years of age. [173]

Calcareous sponges (Calcarea) The largest known of these small, inconspicuous sponges is probably the species Pericharax heteroraphis, attaining a height of 30 cm (0.98 ft). Most calcareous sponges do not exceed 10 cm (3.9 in) tall. [ citation needed ] Hexactinellid sponges (Hexactinellida) A relatively common species, Rhabdocalyptus dawsoni, can reach a height of 1 m (3.3 ft) once they are of a very old age. [174] This is the maximum size recorded for a hexactinellid sponge. [ citation needed ]

Cnidarians (Cnidaria) Edit

The lion's mane jellyfish (Cyanea capillata) is the largest cnidarian species, of the class Scyphozoa. The largest known specimen of this giant, found washed up on the shore of Massachusetts Bay in 1870, [175] [176] had a bell diameter of 2.5 m (8.2 ft), a weight of 150 kg (330 lb). The tentacles of this specimens were as long as 37 m (121 ft) and were projected to have a tentacular spread of about 75 m (246 ft) making it one of the longest extant animals. [8]

Corals and sea anemones (Anthozoa) The largest individual species are the sea-anemones of the genus Discoma, which can attain a mouth disc diameter of 60 cm (2.0 ft). [177] Longer, but much less massive overall, are the anemones of the genus Ceriantharia, at up to 2 m (6.6 ft) tall. [178] Communities of coral can be truly massive, a single colony of the genus Porites can be over 10 m (33 ft), but the actual individual organisms are quite small. Hydrozoans (Hydrozoa) The colonial siphonophore Praya dubia can attain lengths of 40–50 m (130–160 ft). [179] The Portuguese man o' war's (Physalia physalis) tentacles can attain a length of up to 50 m (160 ft). [180] On April 6, 2020 the Schmidt Ocean Institute announced the discovery of a giant Apolemia siphonophore in submarine canyons near Ningaloo Coast, measuring 15 m (49 ft) diameter with a ring approximately 47 m (154 ft) long, claiming it was possibly the largest siphonophore ever recorded. [181] [182]

Flatworms (Platyhelminthes) Edit

Roundworms (Nematoda) Edit

The largest roundworm, Placentonema gigantissima, [187] is a parasite found in the placentas of sperm whales which can reach up to 9 m (30 ft) in length. [188]

Segmented worms (Annelida) Edit

The largest of the segmented worms (including earthworms, leeches, and polychaetes) is the African giant earthworm (Microchaetus rappi). Although it averages about 1.36 m (4.5 ft) in length, this huge worm can reach a length of as much as 6.7 m (22 ft) and can weigh over 1.5 kg (3.3 lb). [189] Only the giant Gippsland earthworm, Megascolides australis, and a few giant polychaetes, including the notorious Eunice aphroditois, reach nearly comparable sizes, reaching 4 and 3.6 m (13 and 12 ft), respectively. [8]

Echinoderms (Echinodermata) Edit

The largest species of echinoderm in terms of bulk is probably the starfish species Thromidia gigas, of the class Asteroidea, which reaches a weight of over 6 kg (13 lb), [190] but it might be beaten by some giant sea cucumbers such as Thelenota anax. However, at a maximum span of 63 cm (25 in), Thromidia gigas is quite a bit shorter than some other echinoderms. [8] The longest echinoderm known is the conspicuous sea cucumber Synapta maculata, with a slender body that can extend up to 3 m (9.8 ft). In comparison, the biggest sea star is the brisingid sea star Midgardia xandaros, reaching a span of 1.4 m (4.6 ft), despite being quite slender. [8] Evasterias echinosoma is another giant echinoderm and can measure up to 1 m (3.3 ft) across and weigh 5.1 kg (11 lb). [8]

Crinoids (Crinoidea) The largest species of crinoid is the unstalked feather-star Heliometra glacialis, reaching a total width of 78 cm (31 in) and an individual arm length of 35 cm (14 in). A width of 91.4 cm (36.0 in) was claimed for one unstalked feather-star but is not confirmed. [8] The genus Metacrinus has a stalk span of 61 cm (24 in) but, due to its bulk and multiple arms, it is heavier than Heliometra. [8] In the past, crinoids grew much larger, and stalk lengths up to 40 m (130 ft) have been found in the fossil record. [191] Sea urchins and allies (Echinoidea) The largest sea urchin is the species Sperosoma giganteum from the deep northwest Pacific Ocean, which can reach a shell width of about 30 cm (12 in). [192] Another deep sea species Hygrosoma hoplacantha is only slightly smaller. [192] The largest species found along the North America coast is the Pacific red sea urchin (Mesocentrotus franciscanus) where the shell can reach 19 cm (7.5 in). [193] If the spines enter into count, the biggest species may be a Diadematidae like Diadema setosum, with a test up to 10 cm (3.9 in) only, but its spines can reach up to 30 cm (12 in) in length. [194] Sea cucumbers (Holothuroidea) The bulkiest species of sea cucumber are Stichopus variegatus and Thelenota anax, weighing several pounds, being about 21 cm (8.3 in) in diameter, and reaching a length of 1 m (3.3 ft) when fully extended. Synapta maculata can reach an extended length of 3 m (9.8 ft), but is extremely slender (3-5cm) and weigh much less than Stichopodids. [8] Brittle stars (Ophiuroidea) The largest known specimen of brittle star is the basket star Astrotoma agassizii. This species can grow to have a span of 1 m (3.3 ft). [8] Sometimes, Gorgonocephalus stimpsoni is considered the largest but the maximum this species is can measure 70 cm (28 in) and a disk diameter of about 14.3 cm (5.6 in). Outside from euryalids, the biggest ophiurid brittle star may be Ophiopsammus maculata (6–7 inches). [195] Sea stars (Asteroidea) The heaviest sea star is Thromidia gigas from the Indo-Pacific, which can surpass 6 kg (13 lb) in weight, but only has a diameter of about 65 cm (2.13 ft). [190] [192] Despite its relatively small disk and weight, the long slender arms of Midgardia xandaros from the Gulf of California makes it the sea star with the largest diameter at about 1.4 m (4.5 ft). [192] Mithrodia clavigera may also become wider than 1 m (39 in) in some cases, with stout arms. [ citation needed ]

Ribbon worms (Nemertea) Edit

The largest nemertean is the bootlace worm, Lineus longissimus. A specimen found washed ashore on a beach in St. Andrews, Scotland in 1864 was recorded at a length of 55 m (180 ft). [196]

Mollusks (Mollusca) Edit

Both the largest mollusks and the largest of all invertebrates (in terms of mass) are the largest squids. The colossal squid (Mesonychoteuthis hamiltoni) is projected to be the largest invertebrate. [197] Current estimates put its maximum size at 12 to 14 m (39 to 46 ft) long and 750 kg (1,650 lb), [198] based on analysis of smaller specimens. In 2007, authorities in New Zealand announced the capture of the largest known colossal squid specimen. It was initially thought to be 10 m (33 ft) and 450 kg (990 lb). It was later measured at 4.2 m (14 ft) long and 495 kg (1,091 lb) in weight. The mantle was 2.5 m (8.2 ft) long when measured. [199] [200]

The giant squid (Architeuthis dux) was previously thought to be the largest squid, and while it is less massive and has a smaller mantle than the colossal squid, it may exceed the colossal squid in overall length including tentacles. One giant squid specimen that washed ashore in 1878 in Newfoundland reportedly measured 16.8 m (55 ft) in total length (from the tip of the mantle to the end of the long tentacles), head and body length 6.1 m (20 ft), 4.6 m (15 ft) in circumference at the thickest part of mantle, and weighed about 900 kg (2,000 lb). This specimen is still often cited as the largest invertebrate that has ever been examined. [8] [201] [202] However, no animals approaching this size have been scientifically documented and, according to giant squid expert Steve O'Shea, such lengths were likely achieved by greatly stretching the two tentacles like elastic bands. [203]

Aplacophorans (Aplacophora) The largest known of these worm-like, shell-less mollusks are represented in the genus Epimenia, which can reach 30 cm (12 in) long. Most aplacophorans are less than 5 cm (2.0 in) long. [204] Chitons (Polyplacophora) The largest of the chitons is the gumboot chiton, Cryptochiton stelleri, which can reach a length of 33 cm (13 in) and weigh over 2 kg (4.4 lb). [205]

Velvet worms (Onychophora) Edit

Solórzano's velvet worm (Peripatus solorzanoi) is the largest velvet worm known. An adult female was recorded to have a body length of 22 cm (approximately 8.7 in). [211]

Arthropods (Arthropoda) Edit

The largest arthropod known to have existed is the eurypterid (sea scorpion) Jaekelopterus, reaching up to 2.5 m (8.2 ft) in body length, followed by the millipede relative Arthropleura at around 2.1 m (6.9 ft) in length. [212] Among living arthropods, the Japanese spider crab (Macrocheira kaempferi) is the largest in overall size, the record specimen, caught in 1921, had an extended arm span of 3.8 m (12 ft) and weighed about 19 kg (42 lb). [8] The heaviest is the American lobster (Homarus americanus), the largest verified specimen, caught in 1977 off of Nova Scotia weighed 20 kg (44 lb) and its body length was 1.1 m (3.6 ft). [8] The largest land arthropod and the largest land invertebrate is the coconut crab (Birgus latro), up to 40 cm (1.3 ft) long and weighing up to 4 kg (8.8 lb) on average. Its legs may span 1 m (3.3 ft). [8]

Arachnids (Arachnida) Edit

Both spiders and scorpions include contenders for the largest arachnids.

Crustaceans (Crustacea) Edit

The largest crustaceans are crab Tasmanian giant crab (''Pseudocarcinus gigas) 13 kilograms (29 lb) and a carapace width of up to 46 centimetres (18 in). It is the only species in the genus Pseudocarcinus. [219] Males reach more than twice the size of females. [220] It has a white shell with claws that are splashed in red. The females' shells change colour when they are producing eggs. At a length of up to 40 centimetres (16 in), Lysiosquillina maculata is the largest mantis shrimp in the world. [221] L. maculata may be distinguished from its congener L. sulcata by the greater number of teeth on the last segment of its raptorial claw, and by the colouration of the uropodal endopod, the distal half of which is dark in L. maculata but not in L. sulcata. [222] There is a small artisanal fishery for this species. [222] Tasmanian giant freshwater crayfish (Astacopsis gouldi) 5 kilograms (11 lb) in weight and over 80 centimetres (31 in) long have been known in the past, but now, even individuals over 2 kilograms (4.4 lb) are rare. [223] The species is only found in Tasmanian rivers flowing north into the Bass Strait below 400 metres (1,300 ft) above sea level, and is listed as an endangered species on the IUCN Red List. [224]

Branchiopods (Branchiopoda) The largest of these primarily freshwater crustaceans is probably Branchinecta gigas, which can reach a length 10 cm (3.9 in). [225] Barnacles and allies (Maxillopoda) The largest species is Pennella balaenopterae, a copepod and ectoparasite specialising in parasitising marine mammals. The maximum size attained is 32 cm (about 13 in). [226] The largest of the barnacles is the giant acorn barnacle, Balanus nubilis, reaching 7 cm (2.8 in) in diameter and 12.7 cm (5.0 in) high. [227] Ostracods (Ostracoda) The largest living representative of these small and little-known but numerous crustaceans is the species Gigantocypris australis females of which reaching a maximum length of 3 cm (1.2 in). Amphipods, isopods, and allies (Peracarida)

Horseshoe crabs (Xiphosura) Edit

The four modern horseshoe crabs are of roughly the same sizes, with females measuring up to 60 cm (2.0 ft) in length and 5 kg (11 lb) in weight. [230]

Sea spiders (Pycnogonida) Edit

The largest of the sea spiders is the deep-sea species Colossendeis colossea, attaining a leg span of nearly 60 cm (2.0 ft). [231]

Trilobites (Trilobita) Edit

Some of these extinct marine arthropods exceeded 60 cm (24 in) in length. A nearly complete specimen of Isotelus rex from Manitoba attained a length over 70 cm (28 in), and an Ogyginus forteyi from Portugal was almost as long. Fragments of trilobites suggest even larger record sizes. An isolated pygidium of Hungioides bohemicus implies that the full animal was 90 cm (35 in) long. [232] [233]

Myriapods (Myriapoda) Edit
Insects (Insecta) Edit

Insects, a class of Arthropoda, are easily the most numerous class of organisms, with over one million identified species, and probably many undescribed species. The heaviest insect is almost certainly a species of beetle, which incidentally is the most species-rich order of organisms. Although heavyweight giant wetas (Deinacrida heteracantha) are known, the elephant beetles of Central and South America, (Megasoma elephas) and (M. actaeon), the Titan beetle (Titanus giganteus) of the neotropical rainforest or the Goliath beetles, (Goliathus goliatus) and (G. regius), of Africa's rainforest are thought to reach a higher weight. [236] The most frequently crowned are the Goliath beetles, the top known size of which is at least 100 g (3.5 oz) and 11.5 cm (4.5 in). [8] The elephant beetles and titan beetle can reach greater lengths than the Goliath, at up to 13.1 and 15.2 cm (5.2 and 6.0 in), respectively, but this is in part thanks to their rather large horns. The Goliath beetle's wingspan can range up to 25 cm (9.8 in). [8]

Some moths and butterflies have much larger areas than the heaviest beetles, but weigh a fraction as much.

The longest insects are the stick insects, see below.

Representatives of the extinct dragonfly-like order Protodonata such as the Carboniferous Meganeura monyi of what is now France and the Permian Meganeuropsis permiana of what is now North America are the largest insect species yet known to have existed. These creatures had a wingspan of some 75 cm (30 in) and a mass of over 1 pound (450 g), making them about the size of a crow. [8]

The largest living fungus may be a honey fungus [269] of the species Armillaria ostoyae. [270] A mushroom of this type in the Malheur National Forest in the Blue Mountains of eastern Oregon, U.S. was found to be the largest fungal colony in the world, spanning 8.9 km 2 (2,200 acres) of area. [271] [272] This organism is estimated to be 2,400 years old. The fungus was written about in the April 2003 issue of the Canadian Journal of Forest Research. While an accurate estimate has not been made, the total weight of the colony may be as much as 605 tons [ vague ] . If this colony is considered a single organism, then it is the largest known organism in the world by area, and rivals the aspen grove "Pando" as the known organism with the highest living biomass. It is not known, however, whether it is a single organism with all parts of the mycelium connected. [272]

A spatial genetic analysis estimated that a specimen of Armillaria ostoyae growing over 91 acres (37 ha) in northern Michigan, United States weighs 440 tons (4 x 10 5 kg). [273] [274] Approximations of the land area of the Oregon "humongous fungus" are 3.5 square miles (9.1 km 2 ) (2,240 acres (910 ha), possibly weighing as much as 35,000 tons as the world's most massive living organism. [275]

In Armillaria ostoyae, each individual mushroom (the fruiting body, similar to a flower on a plant) has only a 5 cm (2.0 in) stipe, and a pileus up to 12.5 cm (4.9 in) across. There are many other fungi which produce a larger individual size mushroom. The largest known fruiting body of a fungus is a specimen of Phellinus ellipsoideus (formerly Fomitiporia ellipsoidea) found on Hainan Island. [276] The fruiting body masses up to 500 kg (1,100 lb). [277] [278]

Until P. ellipsoideus replaced it, the largest individual fruit body came from Rigidoporus ulmarius. R. ulmarius can grow up to 284 kg (626 lb), 1.66 m (5.4 ft) tall, 1.46 m (4.8 ft) across, and has a circumference of up to 4.9 m (16 ft).

(Note: the group Protista is not used in current taxonomy.)

Amoebozoans (Amoebozoa) Edit

Euglenozoans (Euglenozoa) Edit

Rhizarians (Rhizaria) Edit

Alveolates (Alveolata) Edit

Stramenopiles (Stramenopila) Edit

The largest known species of bacterium is Thiomargarita namibiensis, which grows to 0.75 mm (0.030 in) in diameter, making it visible to the naked eye and a thousand times the size of more typical bacteria.

The largest virus on record is the Pithovirus sibericum with the length of 1.5 micrometres, comparable to the typical size of a bacterium and large enough to be seen in light microscopes. It was discovered in March 2014 in an ice core sample collected from a permafrost in Siberia. Prior to this discovery, the largest virus was the peculiar virus genus Pandoravirus, which have a size of approximately 1 micrometer and whose genome contains 1,900,000 to 2,500,000 base pairs of DNA. [286]


Discussion

Our study provides evidences for the existence of a biogeochemically active and dynamic chemoautotrophic bacterial community in the redoxcline of Lake Kivu. Additionally, PLFA analyses shows that the bacterial community composition was structured vertically in the water column, with a large dissimilarity between oxic and anoxic waters, in accordance with previous reports in Lake Kivu based on pyrosequencing (İnceoğlu et al. 2015a, 2015b ). The strong isotopic depletion of the POC pool and C16 MUFA in the oxycline, where the CH4 concentration decreased sharply, indicates that a substantial part of CH4 was consumed and incorporated into the biomass. Indeed, measurements of the CH4 stable isotopic composition and of the methanotrophic bacterial production rates (MBP) carried out with the same set of samples revealed that type I methanotrophs oxidized most of the upward flux of CH4, and vertically integrated MBP values (8.2–29.5 mmol C m −2 d −1 ) were equivalent to 16–60% of the average phytoplankton particulate primary production (Morana et al. 2015 ).

During our study, the maximum volumetric CBP rates were always observed in H2S-rich waters, i.e., below the oxic-anoxic transition zone where the methanotrophic bacterial community was highly active as reported elsewhere (Morana et al. 2015 ). Maximum CBP rates measured in Lake Kivu were within the range of those reported from H2S-rich marine redoxclines, such as the Black Sea (Grote et al. 2008 ), the Baltic Sea (Jost et al. 2008 ), and the Cariaco Basin (Taylor et al 2001 ). Also in these marine systems, the maximal chemoautotrophic activities were observed in sulfidic waters, well below the oxic-anoxic transition zone. In Lake Kivu, oxygen was below the detection limit (< 3 μmol L −1 ) at most of the depths where significant chemoautotrophic production rates were measured, raising the question of which electron acceptors are used by chemoautotrophic organisms in the lower zone of the redoxcline. Recent results (Darchambeau et al. 2014 ) indicate that the density gradient of the mixed layer is usually weak in Lake Kivu, and the stratification of the upper water column is rather unstable. Episodical intrusion of dissolved O2 in the deeper part of the redoxcline could therefore partly fuel aerobic or H2S oxidation. However, in the absence of O2, it is widely assumed that prokaryotes use the thermodynamically most favourable electron acceptors available in waters (Enrich-Prast et al. 2009 ). is commonly the next most energetically favourable electron acceptor in many aquatic environments and it can be used in the anaerobic oxidation of H2S by chemoautotrophic bacteria such as many members of the Epsilonproteobacteria group (Sulfurimonas, Sulfuricurvum), among others. In Lake Kivu, Epsilonproteobacteria were indeed observed in high abundances at the bottom of the redoxcline (İnceoğlu et al. 2015a ,b). Furthermore, the PLFA labelling experiment revealed that CO2 was almost exclusively incorporated in the dark into C16 MUFA at the depths where significant CBP rates were measured. It has actually been already suggested that MUFA are common in gram-negative bacteria (Glaubitz et al. 2009 ) and particularly abundant in sulphur oxidizing bacteria (Li et al. 2007 Glaubitz et al. 2009 ). The biogeochemical importance of chemoautotrophic Epsilonproteobacteria has been also highlighted by microautoradiography in the redoxcline of karstic lakes (Noguerola et al. 2015 ) and marine basins, such as the Black Sea and the Baltic Sea (Grote et al. 2008 ), where they have been found to contribute most to the chemoautotrophic production. Also, in the meromictic Lake Lugano, chemoautotrophic denitrification carried out by proteobacteria members has been identified as the dominant fixed N elimination process in the redoxcline (Wenk et al. 2013 ). We can not totally exclude the possibility that the presence of a trace-level amount of O2 at the start of the incubation led to an overestimate of the CBP rates due the relatively high limit of detection the O2 sensor (3 μmol L −1 ), it nevertheless seems improbable that such a small concentration of O2 could have sustained the relatively large CBP rates measured at the bottom the redoxcline. For instance, assuming that 2 moles of O2 are necessary to oxidize 1 mole of HS − (HS − + 2 O2+ H + ) and using the maximum growth efficiency for sulphide oxiders estimated experimentally found in literature (0.42 mole of CO2 fixed in the biomass per mole of HS - used for energy Kelly 1990 ), a trace level amount of O2 in the incubations bottles (< 3 μmol L −1 ) could not have sustained CBP rates higher than 0.63 μmol C L −1 d −1 . This theoretical aerobic CBP rate is certainly an upper limit but is still ∼ 2 times lower than the CBP rates measured at the bottom of the redoxcline of Lake Kivu, strongly suggesting that other electron acceptors than O2 fueled the chemoautotrophic processes at the bottom of the redoxcline.

Considering theoretical stoichiometries of nitrification and sulphide oxidation, the vertical diffusive and advective fluxes of the main inorganic electron donors ( , 1.95 mmol m −2 d −1 H2S, 0.61 mmol m −2 d −1 ) estimated in the main basin of Lake Kivu by Pasche et al. ( 2009 ) were largely insufficient to fuel the CBP rates measured during this study (19.0 mmol C m −2 d −1 and 13.9 mmol C m −2 d −1 during the rainy and the dry season, respectively). The discrepancy between CBP rates and vertical electron donors fluxes could imply that an intensive, yet cryptic, recycling of S- and N- redox species in the redoxcline must play an important role in Lake Kivu to sustain the chemoautotrophic demand, as suggested for the Black Sea (Murray et al. 1995 ) and the Cariaco basin (Li et al. 2012 ). Indeed, despite their biogeochemical significance in the water column, these processes would not have any clear in situ chemical expression because of the tight coupling between production and consumption of the chemical species used by the chemoautotrophs.

With the exception of the Kabuno Bay basin, characterized by a more shallow and well-illuminated redoxcline, measurable rates of anoxygenic photosynthesis were never detected in Lake Kivu during this study. This might be related to the very low light availability at the oxic-anoxic transition zone in Lake Kivu and competition between different microbial communities for available resources. Indeed, considering a light attenuation coefficient of 0.26 m −1 (Darchambeau et al. 2014 ), the estimated light intensity at the oxic-anoxic transition zone was estimated at 6.66 × 10 −3 μmol photon m −2 s −1 for the rainy season (in February 2012) and 3 × 10 −5 μmol photon m −2 s −1 for the dry season (in September 2012), well below the values reported in the chemocline of the Black Sea (∼ 0.18 μmol photon m −2 s −1 ), Lake Matano (∼ 0.12 μmol photon m −2 s −1 ), and Kabuno Bay (0.6 μmol photon m −2 s −1 ), where low-light adapted Chlorobium species were identified (Marschall et al. 2010 Crowe et al. 2014 Llirós et al. 2015 ).

Kabuno Bay was characterized by AnPBP rates an order of magnitude higher than CBP rates. The strong 13 C-labelling during the tracer experiments of the C14:0, C16:0, and C16 MUFA, which were also naturally enriched in 13 C under in situ conditions, indicates that the bacteria responsible for the anoxygenic photosynthetic CO2 fixation were members of the Chlorobium genus. Indeed, these fatty acids are usually highly abundant in Chlorobium (Imhoff 2003 ), and they are known to use the reverse tricarboxylic cycle (rTCA) pathway to fix C into the cellular biomass. This alternative C fixation pathway is less discriminating against 13 C than other photosynthetic pathway, such as the Calvin cycle (Sirevåg et al. 1977 ). Considering the isotope fractionation factor for C fixation by Chlorobium via the rTCA pathway (−12.2‰, Sirevåg et al. 1977 ) and the measured δ 13 C-DIC values below the oxycline in Kabuno Bay during this study (−5.4 ± 0.3‰, n = 6), we estimated that the theoretical isotopic signature of the biomass fixed by Chlorobium should approximate −17‰ in Kabuno Bay. Therefore, using a simple isotope mixing model with the δ 13 C-POC in surface as a sedimenting organic matter end-member and the δ 13 C signature of Chlorobium as a second end-member, it could be estimated that 74% ± 13% of the POC pool below the oxycline originated from anoxygenic photosynthesis, with a maximum at 11.25 m (89%). Furthermore, when integrated from the surface to the bottom of the redoxcline (12.00 m), the data revealed that 23% of the POC pool of the water column was derived from anoxygenic CO2 fixation by Chlorobium. Altogether, these results gathered from stable isotope analysis stress the important role played by Chlorobium in the C cycle of Kabuno Bay, as recently evidenced by molecular and culturing approaches (Llirós et al. 2015 ).

A relatively high abundance of cy17:0 (reaching 10%) was found below the oxycline of Kabuno Bay, whereas this PLFA was undetectable in the main basin of Lake Kivu. Furthermore, this PLFA was naturally enriched in 13 C in the water column (−9.5 ± 1.2‰, n = 5), reflecting its almost exclusive presence in Chlorobium cellular membranes however, it was never labelled during the 13 C-tracer experiment (Fig. 7). It has been shown that cy17:0 is directly synthesized from C16 MUFA by modification of the cis double bond, but cyclopropane ring formation in bacterial membranes has a high energetic cost. The cyclopropane bond is more stable than a double bond and plays a crucial role in protection against thermal, acidic, oxidative, or salt stress (Grogan and Cronan 1997 Zhang and Rock 2008 ). In anoxygenic phototrophs, the cyclopropane ring has notably been found to reinforce the resistance of the light-harvesting chlorosome to different types of environmental stress (Mizoguchi et al. 2013 ) and its production typically occurs when bacterial cells encounter starvation or others forms of growth stasis (Grogan and Cronan 1997 ). Overall, it is generally assumed that the main physiological function of cyclopropane fatty acids is to improve the viability of slow-growing or quiescent cells (Zhang and Rock 2008 ). However, once formed, cyclopropane fatty acids appear to be extremely stable molecules, so that they remain in the cell membrane even after return to more favourable environmental conditions (Grogan and Cronan 1997 ). The absence of isotopic labelling of the cy17:0 during the 24 h incubation carried out during this study is consistent with this idea. Therefore, the relative increase of the proportion of cy17:0 relative to its precursor (C16 MUFA) found below the oxycline could indicate that a non-negligible fraction of the anoxygenic phototroph community had been subjected to environmental stress during their life span. For instance, we might consider that light attenuation induced by the physico-chemical structure of the water column, scattering by organic and inorganic particles, and self-shading, would affect the growth of the anoxygenic phototrophs present at the bottom of the redoxcline, as demonstrated in the ferruginous Lake Matano (Crowe et al. 2014 ).

(3)
H2S Fe 2+
Upward flux (mmol m −2 d −1 ) 0.02–0.14 5–37
Oxidation product S 0 Fe 3+
Reaction stoichiometry (ed:CO2) 2 0.5 4
Areal anPBP (mmol m −2 d −1 ) 2.9 2.9 2.9
% of anPBP sustained by upward flux 0–2 1–10 43–318

In summary, chemoautotrophy in the pelagic redoxcline of Lake Kivu is significant, and may affect the ecological functioning of Lake Kivu in several ways. First, chemoautotrophs may represent alternative sources of autochtonous organic matter for higher trophic levels, besides oxygenic photosynthesis carried out by phytoplankton in the surface waters. Second, they could exert an indirect control on phytoplankton production by limiting the amount of inorganic nutrients that reach the illuminated surface waters through diffusion from bottom waters. This shortcircuiting of the vertical nutrient transport seems to be specially important in the large East African Rift lakes where internal nutrient loading via upward fluxes is of major importance for phytoplankton growth (Kilham and Kilham 1990 Pasche et al. 2009 ). For instance, if chemoautotrophic uptake of dissolved inorganic phosphorus (DIP) follows Redfield stoechiometry (C : P = 106 : 1), chemoautotrophic DIP uptake in the redoxcline of the main basin would have approximated 0.18 mmol P m −2 d −1 and 0.13 mmol P m −2 d −1 in February and September 2012, respectively. This DIP uptake flux is higher than the upward DIP flux of 0.08 mmol m −2 d −1 estimated by Pasche et al. ( 2009 ) highlighting the importance of the control that chemoautotrophs might exert on nutrient availability in the mixed layer, but it also suggests that a substantial amount of inorganic nutrients has to be actively recycled within the redoxcline to sustain the chemoautotrophic demand.

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Research unlocks the genomic secrets of organisms that thrive in extreme deep-sea

The drawing shows a clam with its foot extending deep into the sediment to gain access to hydrogen sulfide. The foot and mantle of the clam are red due to the presence of hemoglobin for gas transport in the blood, which is an adaptation to the low-oxygen environment. Credit: Hu Juntong

A study led by scientists at Hong Kong Baptist University (HKBU) has decoded the genomes of the deep-sea clam (Archivesica marissinica) and the chemoautotrophic bacteria (Candidatus Vesicomyosocius marissinica) that live in its gill epithelium cells. Through analysis of their genomic structures and profiling of their gene expression patterns, the research team revealed that symbiosis between the two partners enables the clams to thrive in extreme deep-sea environments.

The research findings have been published in the academic journal Molecular Biology and Evolution.

Due to the general lack of photosynthesis-derived organic matter, the deep-sea was once considered a vast 'desert' with very little biomass. Yet, clams often form large populations in the high-temperature hydrothermal vents and freezing cold seeps in the deep oceans around the globe where sunlight cannot penetrate but toxic molecules, such as hydrogen sulfide, are available below the seabed. The clams are known to have a reduced gut and digestive system, and they rely on endosymbiotic bacteria to generate energy in a process called chemosynthesis. However, when this symbiotic relationship developed, and how the clams and chemoautotrophic bacteria interact, remain largely unclear.

Horizontal gene transfer between bacteria and clams discovered for the first time

A research team led by Professor Qiu Jianwen, Associate Head and Professor of the Department of Biology at HKBU, collected the clam specimens at 1,360 meters below sea level from a cold seep in the South China Sea. The genomes of the clam and its symbiotic bacteria were then sequenced to shed light on the genomic signatures of their successful symbiotic relationship.

The team found that the ancestor of the clam split with its shallow-water relatives 128 million years ago when dinosaurs roamed the earth. The study revealed that 28 genes have been transferred from the ancestral chemoautotrophic bacteria to the clam, the first discovery of horizontal gene transfer—a process that transmits genetic material between distantly-related organisms —from bacteria to a bivalve mollusc.

The following genomic features of the clam were discovered, and combined, they have enabled it to adapt to the extreme deep-sea environment.

Professor Qiu Jianwen (right) and his HKBU research team member Dr Ip Chi-ho (centre) and Dr Xu Ting collect the clam specimens at 1,360 meters below the sea level from the South China Sea. Credit: Hong Kong Baptist University

Adaptions for chemosynthesis

The clam relies on its symbiotic chemoautotrophic bacteria to produce the biological materials essential for its survival. In their symbiotic relationship, the clam absorbs hydrogen sulfide from the sediment, and oxygen and carbon dioxide from seawater, and it transfers them to the bacteria living in its gill epithelium cells to produce the energy and nutrients in a process called chemosynthesis. The process is illustrated in Figure 1.

The research team also discovered that the clam's genome exhibits gene family expansion in cellular processes such as respiration and diffusion that likely facilitate chemoautotrophy, including gas delivery to support energy and carbon production, the transfer of small molecules and proteins within the symbiont, and the regulation of the endosymbiont population. It helps the host to obtain sufficient nutrients from the symbiotic bacteria.

Shift from phytoplankton-based food

Cellulase is an enzyme that facilitates the decomposition of the cellulose found in phytoplankton, a major primary food source in the marine food chain. It was discovered that the clam's cellulase genes have undergone significant contraction, which is likely an adaptation to the shift from phytoplankton-derived to bacteria-based food.

Adaptation to sulfur metabolic pathways

The genome of the symbiont also holds the secrets of this mutually beneficial relationship. The team discovered that the clam has a reduced genome, as it is only about 40% of the size of its free-living relatives. Nevertheless, the symbiont genome encodes complete and flexible sulfur metabolic pathways, and it retains the ability to synthesise 20 common amino acids and other essential nutrients, highlighting the importance of the symbiont in generating energy and providing nutrients to support the symbiotic relationship.

Improvement in oxygen-binding capacity

Unlike in vertebrates, haemoglobin, a metalloprotein found in the blood and tissues of many organisms, is not commonly used as an oxygen carrier in molluscs. However, the team discovered several kinds of highly expressed haemoglobin genes in the clam, suggesting an improvement in its oxygen-binding capacity, which can enhance the ability of the clam to survive in deep-sea low-oxygen habitats.

Professor Qiu said: "Most of the previous studies on deep-sea symbiosis have focused only on the bacteria. This first coupled clam-symbiont genome assembly will facilitate comparative studies that aim to elucidate the diversity and evolutionary mechanisms of symbiosis, which allows many invertebrates to thrive in 'extreme' deep-sea ecosystems."


46.2 Energy Flow through Ecosystems

By the end of this section, you will be able to do the following:

  • Describe how organisms acquire energy in a food web and in associated food chains
  • Explain how the efficiency of energy transfers between trophic levels affects ecosystem structure and dynamics
  • Discuss trophic levels and how ecological pyramids are used to model them

All living things require energy in one form or another. Energy is required by most complex metabolic pathways (often in the form of adenosine triphosphate, ATP), especially those responsible for building large molecules from smaller compounds, and life itself is an energy-driven process. Living organisms would not be able to assemble macromolecules (proteins, lipids, nucleic acids, and complex carbohydrates) from their monomeric subunits without a constant energy input.

It is important to understand how organisms acquire energy and how that energy is passed from one organism to another through food webs and their constituent food chains. Food webs illustrate how energy flows directionally through ecosystems, including how efficiently organisms acquire it, use it, and how much remains for use by other organisms of the food web.

How Organisms Acquire Energy in a Food Web

Energy is acquired by living things in three ways: photosynthesis, chemosynthesis, and the consumption and digestion of other living or previously living organisms by heterotrophs.

Photosynthetic and chemosynthetic organisms are both grouped into a category known as autotrophs: organisms capable of synthesizing their own food (more specifically, capable of using inorganic carbon as a carbon source). Photosynthetic autotrophs (photoautotrophs) use sunlight as an energy source, whereas chemosynthetic autotrophs (chemoautotrophs) use inorganic molecules as an energy source. Autotrophs are critical for all ecosystems. Without these organisms, energy would not be available to other living organisms and life itself would not be possible.

Photoautotrophs, such as plants, algae, and photosynthetic bacteria, serve as the energy source for a majority of the world’s ecosystems. These ecosystems are often described by grazing food webs. Photoautotrophs harness the solar energy of the sun by converting it to chemical energy in the form of ATP (and NADP). The energy stored in ATP is used to synthesize complex organic molecules, such as glucose.

Chemoautotrophs are primarily bacteria that are found in rare ecosystems where sunlight is not available, such as in those associated with dark caves or hydrothermal vents at the bottom of the ocean (Figure 46.9). Many chemoautotrophs in hydrothermal vents use hydrogen sulfide (H2S), which is released from the vents as a source of chemical energy. This allows chemoautotrophs to synthesize complex organic molecules, such as glucose, for their own energy and in turn supplies energy to the rest of the ecosystem.

Productivity within Trophic Levels

Productivity within an ecosystem can be defined as the percentage of energy entering the ecosystem incorporated into biomass in a particular trophic level. Biomass is the total mass, in a unit area at the time of measurement, of living or previously living organisms within a trophic level. Ecosystems have characteristic amounts of biomass at each trophic level. For example, in the English Channel ecosystem the primary producers account for a biomass of 4 g/m 2 (grams per square meter), while the primary consumers exhibit a biomass of 21 g/m 2 .

The productivity of the primary producers is especially important in any ecosystem because these organisms bring energy to other living organisms by photoautotrophy or chemoautotrophy. The rate at which photosynthetic primary producers incorporate energy from the sun is called gross primary productivity . An example of gross primary productivity is shown in the compartment diagram of energy flow within the Silver Springs aquatic ecosystem as shown (Figure 46.8). In this ecosystem, the total energy accumulated by the primary producers (gross primary productivity) was shown to be 20,810 kcal/m 2 /yr.

Because all organisms need to use some of this energy for their own functions (like respiration and resulting metabolic heat loss) scientists often refer to the net primary productivity of an ecosystem. Net primary productivity is the energy that remains in the primary producers after accounting for the organisms’ respiration and heat loss. The net productivity is then available to the primary consumers at the next trophic level. In our Silver Springs example, 13,187 of the 20,810 kcal/m 2 /yr were used for respiration or were lost as heat, leaving 7,633 kcal/m 2 /yr of energy for use by the primary consumers.

Ecological Efficiency: The Transfer of Energy between Trophic Levels

As illustrated in (Figure 46.8), as energy flows from primary producers through the various trophic levels, the ecosystem loses large amounts of energy. The main reason for this loss is the second law of thermodynamics, which states that whenever energy is converted from one form to another, there is a tendency toward disorder (entropy) in the system. In biologic systems, this energy takes the form of metabolic heat, which is lost when the organisms consume other organisms. In the Silver Springs ecosystem example (Figure 46.8), we see that the primary consumers produced 1103 kcal/m 2 /yr from the 7618 kcal/m 2 /yr of energy available to them from the primary producers. The measurement of energy transfer efficiency between two successive trophic levels is termed the trophic level transfer efficiency (TLTE) and is defined by the formula:

In Silver Springs, the TLTE between the first two trophic levels was approximately 14.8 percent. The low efficiency of energy transfer between trophic levels is usually the major factor that limits the length of food chains observed in a food web. The fact is, after four to six energy transfers, there is not enough energy left to support another trophic level. In the Lake Ontario example shown in (Figure 46.6), only three energy transfers occurred between the primary producer, (green algae), and the apex consumer (Chinook salmon).

Ecologists have many different methods of measuring energy transfers within ecosystems. Measurement difficulty depends on the complexity of the ecosystem and how much access scientists have to observe the ecosystem. In other words, some ecosystems are more difficult to study than others, and sometimes the quantification of energy transfers has to be estimated.

Other parameters are important in characterizing energy flow within an ecosystem. Net production efficiency (NPE) allows ecologists to quantify how efficiently organisms of a particular trophic level incorporate the energy they receive into biomass it is calculated using the following formula:

Net consumer productivity is the energy content available to the organisms of the next trophic level. Assimilation is the biomass (energy content generated per unit area) of the present trophic level after accounting for the energy lost due to incomplete ingestion of food, energy used for respiration, and energy lost as waste. Incomplete ingestion refers to the fact that some consumers eat only a part of their food. For example, when a lion kills an antelope, it will eat everything except the hide and bones. The lion is missing the energy-rich bone marrow inside the bone, so the lion does not make use of all the calories its prey could provide.

Thus, NPE measures how efficiently each trophic level uses and incorporates the energy from its food into biomass to fuel the next trophic level. In general, cold-blooded animals (ectotherms), such as invertebrates, fish, amphibians, and reptiles, use less of the energy they obtain for respiration and heat than warm-blooded animals (endotherms), such as birds and mammals. The extra heat generated in endotherms, although an advantage in terms of the activity of these organisms in colder environments, is a major disadvantage in terms of NPE. Therefore, many endotherms have to eat more often than ectotherms to get the energy they need for survival. In general, NPE for ectotherms is an order of magnitude (10x) higher than for endotherms. For example, the NPE for a caterpillar eating leaves has been measured at 18 percent, whereas the NPE for a squirrel eating acorns may be as low as 1.6 percent.

The inefficiency of energy use by warm-blooded animals has broad implications for the world's food supply. It is widely accepted that the meat industry uses large amounts of crops to feed livestock, and because the NPE is low, much of the energy from animal feed is lost. For example, it costs about .01 to produce 1000 dietary calories (kcal) of corn or soybeans, but approximately .19 to produce a similar number of calories growing cattle for beef consumption. The same energy content of milk from cattle is also costly, at approximately .16 per 1000 kcal. Much of this difference is due to the low NPE of cattle. Thus, there has been a growing movement worldwide to promote the consumption of nonmeat and nondairy foods so that less energy is wasted feeding animals for the meat industry.

Modeling Ecosystems Energy Flow: Ecological Pyramids

The structure of ecosystems can be visualized with ecological pyramids, which were first described by the pioneering studies of Charles Elton in the 1920s. Ecological pyramids show the relative amounts of various parameters (such as number of organisms, energy, and biomass) across trophic levels.

Pyramids of numbers can be either upright or inverted, depending on the ecosystem. As shown in Figure 46.10, typical grassland during the summer has a base of many plants, and the numbers of organisms decrease at each trophic level. However, during the summer in a temperate forest, the base of the pyramid consists of few trees compared with the number of primary consumers, mostly insects. Because trees are large, they have great photosynthetic capability, and dominate other plants in this ecosystem to obtain sunlight. Even in smaller numbers, primary producers in forests are still capable of supporting other trophic levels.

Another way to visualize ecosystem structure is with pyramids of biomass. This pyramid measures the amount of energy converted into living tissue at the different trophic levels. Using the Silver Springs ecosystem example, this data exhibits an upright biomass pyramid (Figure 46.10), whereas the pyramid from the English Channel example is inverted. The plants (primary producers) of the Silver Springs ecosystem make up a large percentage of the biomass found there. However, the phytoplankton in the English Channel example make up less biomass than the primary consumers, the zooplankton. As with inverted pyramids of numbers, this inverted pyramid is not due to a lack of productivity from the primary producers, but results from the high turnover rate of the phytoplankton. The phytoplankton are consumed rapidly by the primary consumers, thus, minimizing their biomass at any particular point in time. However, phytoplankton reproduce quickly, thus they are able to support the rest of the ecosystem.

Pyramid ecosystem modeling can also be used to show energy flow through the trophic levels. Notice that these numbers are the same as those used in the energy flow compartment diagram in (Figure 46.8). Pyramids of energy are always upright, and an ecosystem without sufficient primary productivity cannot be supported. All types of ecological pyramids are useful for characterizing ecosystem structure. However, in the study of energy flow through the ecosystem, pyramids of energy are the most consistent and representative models of ecosystem structure (Figure 46.10).

Visual Connection

Pyramids depicting the number of organisms or biomass may be inverted, upright, or even diamond-shaped. Energy pyramids, however, are always upright. Why?

Consequences of Food Webs: Biological Magnification

One of the most important environmental consequences of ecosystem dynamics is biomagnification. Biomagnification is the increasing concentration of persistent, toxic substances in organisms at each trophic level, from the primary producers to the apex consumers. Many substances have been shown to bioaccumulate, including the pesticide dichlorodiphenyltrichloroethane (DDT), which was described in the 1960s bestseller, Silent Spring, by Rachel Carson. DDT was a commonly used pesticide before its dangers became known. In some aquatic ecosystems, organisms from each trophic level consumed many organisms of the lower level, which caused DDT to increase in birds (apex consumers) that ate fish. Thus, the birds accumulated sufficient amounts of DDT to cause fragility in their eggshells. This effect increased egg breakage during nesting and was shown to have adverse effects on these bird populations. The use of DDT was banned in the United States in the 1970s.

Other substances that biomagnify are polychlorinated biphenyls (PCBs), which were used in coolant liquids in the United States until their use was banned in 1979, and heavy metals, such as mercury, lead, and cadmium. These substances were best studied in aquatic ecosystems, where fish species at different trophic levels accumulate toxic substances brought through the ecosystem by the primary producers. As illustrated in a study performed by the National Oceanic and Atmospheric Administration (NOAA) in the Saginaw Bay of Lake Huron (Figure 46.11), PCB concentrations increased from the ecosystem’s primary producers (phytoplankton) through the different trophic levels of fish species. The apex consumer (walleye) has more than four times the amount of PCBs compared to phytoplankton. Also, based on results from other studies, birds that eat these fish may have PCB levels at least one order of magnitude higher than those found in the lake fish.

Other concerns have been raised by the accumulation of heavy metals, such as mercury and cadmium, in certain types of seafood. The United States Environmental Protection Agency (EPA) recommends that pregnant women and young children should not consume any swordfish, shark, king mackerel, or tilefish because of their high mercury content. These individuals are advised to eat fish low in mercury: salmon, tilapia, shrimp, pollock, and catfish. Biomagnification is a good example of how ecosystem dynamics can affect our everyday lives, even influencing the food we eat.


ECOLOGY

Ecosystem - An environment/space where biotic and abiotic factors interact.

Ecology - Study of biotic factors and their relationship/interaction with abiotic factors.

Species - Group of organisms which are capable of interbreeding and producing fertile offspring.

Population - A group of organisms of the same species in the same area at the same time.

Community - Different populations in the same habitat, interacting together.

Habitat - Environment in which a species normally lives.

Biosphere - Multiple ecosystems interacting with each other.

Cells Tissues Organs Organ Systems Organism

Species Population Community Ecosystem Biosphere

Autotrophs - Capable of making their own organic molecules from inorganic molecules as a food source.

Heterotrophs - Cannot make their own food and must obtain organic molecules from other organisms.

Herbivores - An animal that gets its energy from eating plants and only plants.

Omnivores - An animal that gets its energy from eating both plants and other animals.

Carnivores - An animal that gets its energy from eating only other animals.

Food Chains - A linear network of links in a food web starting from producer organisms and ending at apex predator species, detritivores, or decomposer species.

Food Webs - A system of interlocking and interdependent food chains.

Consumers - Ingest organic matter which is living or has recently died, in order to live. The three types of consumers are herbivores, omnivores, and carnivores.

Trophic levels - Energy levels

Decomposers - Consume dead material, recycles nutrients back to the environment.

Saprotrophs - Secrete digestive enzymes in surroundings and absorb nutrients (e.g. fungus)

Detrivores - First consumes food, then digests it inside bosy (e.g. insects)

Detritus - Dead organic material

Photoautotrophy - Derive energy through photosynthesis.

Chemoautotrophy - Derive energy stored in chemical bonds.

Chemical energy in carbon compounds flow through food chains by means of feeding.

* Energy is non-cyclic, comes from the sun.

Transfer of energy from one trophic level to the next.

Only 10% of energy is transferred from one trophic level to the next because the other 90% of energy is used up by the organism being eaten. Also note that animals do not completely eat the entire animal, some parts of animal are uneaten.


The authors would like to thank all the members of Dominica Scientific Expedition in April 2013 (J. Amend, C. Kleint, A. Koschinsky, T. Pichler, M. Sollich and S. Sztejrenszus). Thanks to the Dominican Department of Fisheries, especially to A. Magloire for granting sample permission, O. Lugay for providing logistical support and A. Madisetti for joining the sampling with underwater photography. Special thanks to B. Dieterich, X. Prieto-Mollar, and J. Wendt for laboratory assistance and to L. Wörmer and F. Schubotz for valuable advices. C. Quast is thanked for his help with sequence processing though the SILVAngs pipeline and M. W. Friedrich for providing facilities to perform molecular laboratory work. We also thank the two reviewers whose comments helped to improve an earlier version of this manuscript.

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Keywords : chemoautotrophy, marine shallow-water hydrothermal systems, lipid biomarker, stable isotope probing (SIP), fatty acids, Dominica (Lesser Antilles), Zetaproteobacteria, Geothermobacter

Citation: Gomez-Saez GV, Pop Ristova P, Sievert SM, Elvert M, Hinrichs K-U and Bühring SI (2017) Relative Importance of Chemoautotrophy for Primary Production in a Light Exposed Marine Shallow Hydrothermal System. Front. Microbiol. 8:702. doi: 10.3389/fmicb.2017.00702

Received: 30 January 2017 Accepted: 05 April 2017
Published: 21 April 2017.

David Emerson, Bigelow Laboratory for Ocean Sciences, USA

Sean M. McAllister, University of Delaware, USA
D𠆚rcy Renee Meyer-Dombard, University of Illinois at Chicago, USA

Copyright © 2017 Gomez-Saez, Pop Ristova, Sievert, Elvert, Hinrichs and Bühring. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) or licensor are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

† Present address: Gonzalo V. Gomez-Saez, Research Group for Marine Geochemistry (ICBM – MPI Bridging Group), Institute for Chemistry and Biology of the Marine Environment, Carl von Ossietzky University of Oldenburg, Oldenburg, Germany


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