HOME

TheInfoList



OR:

In
zoology Zoology ()The pronunciation of zoology as is usually regarded as nonstandard, though it is not uncommon. is the branch of biology that studies the animal kingdom, including the structure, embryology, evolution, classification, habits, and dis ...
, deep-sea gigantism or abyssal gigantism is the tendency for species of
invertebrate Invertebrates are a paraphyletic group of animals that neither possess nor develop a vertebral column (commonly known as a ''backbone'' or ''spine''), derived from the notochord. This is a grouping including all animals apart from the chordate ...
s and other deep-sea dwelling animals to be larger than their shallower-water relatives across a large taxonomic range. Proposed explanations for this type of gigantism include colder temperature, food scarcity, reduced predation pressure and increased dissolved oxygen concentrations in the deep sea. The inaccessibility of
abyssal The abyssal zone or abyssopelagic zone is a layer of the pelagic zone of the ocean. "Abyss" derives from the Greek word , meaning bottomless. At depths of , this zone remains in perpetual darkness. It covers 83% of the total area of the ocean an ...
habitats has hindered the study of this topic.


Taxonomic range

In marine
crustacean Crustaceans (Crustacea, ) form a large, diverse arthropod taxon which includes such animals as decapods, seed shrimp, branchiopods, fish lice, krill, remipedes, isopods, barnacles, copepods, amphipods and mantis shrimp. The crustacean group ...
s, the trend of increasing size with depth has been observed in
mysid Mysida is an order of small, shrimp-like crustaceans in the malacostracan superorder Peracarida. Their common name opossum shrimps stems from the presence of a brood pouch or "marsupium" in females. The fact that the larvae are reared in this ...
s, euphausiids, decapods,
isopod Isopoda is an order of crustaceans that includes woodlice and their relatives. Isopods live in the sea, in fresh water, or on land. All have rigid, segmented exoskeletons, two pairs of antennae, seven pairs of jointed limbs on the thorax, an ...
s and
amphipod Amphipoda is an order of malacostracan crustaceans with no carapace and generally with laterally compressed bodies. Amphipods range in size from and are mostly detritivores or scavengers. There are more than 9,900 amphipod species so far descri ...
s. Non-arthropods in which deep-sea gigantism has been observed are
cephalopod A cephalopod is any member of the molluscan class Cephalopoda (Greek plural , ; "head-feet") such as a squid, octopus, cuttlefish, or nautilus. These exclusively marine animals are characterized by bilateral body symmetry, a prominent head, a ...
s,
cnidaria Cnidaria () is a phylum under kingdom Animalia containing over 11,000 species of aquatic animals found both in freshwater and marine environments, predominantly the latter. Their distinguishing feature is cnidocytes, specialized cells that th ...
ns, and eels from the order Anguilliformes. Examples of deep-sea gigantism include the big red jellyfish, the giant isopod, giant ostracod, the giant sea spider, the giant amphipod, the
Japanese spider crab The Japanese spider crab (''Macrocheira kaempferi'') is a species of marine crab that lives in the waters around Japan. It has the largest known leg-span of any arthropod. It goes through three main larval stages along with a prezoeal stage to g ...
, the
giant oarfish The giant oarfish (''Regalecus glesne'') is a species of oarfish of the family Regalecidae. It is an oceanodromous species with a worldwide distribution, excluding polar regions. Other common names include Pacific oarfish, king of herrings, rib ...
, the deepwater stingray, the
seven-arm octopus The seven-arm octopus (''Haliphron atlanticus'') is one of the two largest known species of octopus; based on scientific records, it has a maximum estimated total length of and mass of . The only other similarly large extant species is the gia ...
, and a number of squid species: the
colossal squid The colossal squid (''Mesonychoteuthis hamiltoni'') is part of the family Cranchiidae. It is sometimes called the Antarctic squid or giant cranch squid and is believed to be the largest squid species in terms of mass. It is the only recognize ...
(up to 14 m in length), the
giant squid The giant squid (''Architeuthis dux'') is a species of deep-ocean dwelling squid in the family Architeuthidae. It can grow to a tremendous size, offering an example of abyssal gigantism: recent estimates put the maximum size at around Trace ...
(up to 12 m), '' Onykia robusta'', '' Taningia danae'', '' Galiteuthis phyllura'', '' Kondakovia longimana'', and the
bigfin squid Bigfin squids are a group of rarely seen cephalopods with a distinctive morphology. They are placed in the genus ''Magnapinna'' and family Magnapinnidae. Although the family is known only from larval, paralarval, and juvenile specimens, some a ...
. Deep-sea gigantism is not generally observed in the
meiofauna Meiobenthos, also called meiofauna, are small benthic invertebrates that live in both marine and fresh water environments. The term ''meiofauna'' loosely defines a group of organisms by their size, larger than microfauna but smaller than macrofau ...
(organisms that pass through a 1 mm mesh), which actually exhibit the reverse trend of decreasing size with depth.


Explanations


Lower temperature

In crustaceans, it has been proposed that the explanation for the increase in size with depth is similar to that for the increase in size with
latitude In geography, latitude is a coordinate that specifies the north– south position of a point on the surface of the Earth or another celestial body. Latitude is given as an angle that ranges from –90° at the south pole to 90° at the north ...
(
Bergmann's rule Bergmann's rule is an ecogeographical rule that states that within a broadly distributed taxonomic clade, populations and species of larger size are found in colder environments, while populations and species of smaller size are found in warmer ...
): both trends involve increasing size with decreasing temperature. The trend with latitude has been observed in some of the same groups, both in comparisons of related species, as well as within widely distributed species. Decreasing temperature is thought to result in increased
cell Cell most often refers to: * Cell (biology), the functional basic unit of life Cell may also refer to: Locations * Monastic cell, a small room, hut, or cave in which a religious recluse lives, alternatively the small precursor of a monastery w ...
size and increased life span (the latter also being associated with delayed sexual maturity), both of which lead to an increase in maximum body size (continued growth throughout life is characteristic of crustaceans). In
Arctic The Arctic ( or ) is a polar region located at the northernmost part of Earth. The Arctic consists of the Arctic Ocean, adjacent seas, and parts of Canada (Yukon, Northwest Territories, Nunavut), Danish Realm (Greenland), Finland, Iceland, N ...
and
Antarctic The Antarctic ( or , American English also or ; commonly ) is a polar region around Earth's South Pole, opposite the Arctic region around the North Pole. The Antarctic comprises the continent of Antarctica, the Kerguelen Plateau and other ...
seas where there is a reduced vertical temperature gradient, there is also a reduced trend towards increased body size with depth, arguing against
hydrostatic pressure Fluid statics or hydrostatics is the branch of fluid mechanics that studies the condition of the equilibrium of a floating body and submerged body "fluids at hydrostatic equilibrium and the pressure in a fluid, or exerted by a fluid, on an imme ...
being an important parameter. Temperature does not appear to have a similar role in influencing the size of giant tube worms. ''
Riftia pachyptila ''Riftia pachyptila'', commonly known as the giant tube worm and less commonly known as the Giant beardworm, is a marine invertebrate in the phylum Annelida (formerly grouped in phylum Pogonophora and Vestimentifera) related to tube worms ...
'', which lives in
hydrothermal vent A hydrothermal vent is a fissure on the seabed from which geothermally heated water discharges. They are commonly found near volcanically active places, areas where tectonic plates are moving apart at mid-ocean ridges, ocean basins, and hotspot ...
communities at ambient temperatures of 2–30 °C, reaches lengths of 2.7 m, comparable to those of ''
Lamellibrachia luymesi ''Lamellibrachia luymesi'' is a species of tube worms in the family Siboglinidae. It lives at deep-sea cold seeps where hydrocarbons (oil and methane) are leaking out of the seafloor. It is entirely reliant on internal, sulfide-oxidizing bacte ...
'', which lives in
cold seep A cold seep (sometimes called a cold vent) is an area of the ocean floor where hydrogen sulfide, methane and other hydrocarbon-rich fluid seepage occurs, often in the form of a brine pool. ''Cold'' does not mean that the temperature of the see ...
s. The former, however, has rapid growth rates and short life spans of about 2 years, while the latter is slow growing and may live over 250 years.


Food scarcity

Food scarcity at depths greater than 400 m is also thought to be a factor, since larger body size can improve ability to forage for widely scattered resources. In organisms with
plankton Plankton are the diverse collection of organisms found in water (or air) that are unable to propel themselves against a current (or wind). The individual organisms constituting plankton are called plankters. In the ocean, they provide a crucia ...
ic eggs or larvae, another possible advantage is that larger offspring, with greater initial stored food reserves, can drift for greater distances. As an example of adaptations to this situation, giant isopods gorge on food when available, distending their bodies to the point of compromising ability to locomote; they can also survive 5 years without food in captivity. According to
Kleiber's law Kleiber's law, named after Max Kleiber for his biology work in the early 1930s, is the observation that, for the vast majority of animals, an animal's metabolic rate scales to the power of the animal's mass. Symbolically: if is the animal's met ...
, the larger an animal gets, the more efficient its metabolism becomes; i.e., an animal's basal metabolic rate scales to roughly the ¾ power of its mass. Under conditions of limited food supply, this may provide additional benefit to large size.


Reduced predation pressure

An additional possible influence is reduced predation pressure in deeper waters. A study of
brachiopod Brachiopods (), phylum Brachiopoda, are a phylum of trochozoan animals that have hard "valves" (shells) on the upper and lower surfaces, unlike the left and right arrangement in bivalve molluscs. Brachiopod valves are hinged at the rear end, wh ...
s found that predation was nearly an order of magnitude less frequent at the greatest depths than in shallow waters.


Increased dissolved oxygen

Dissolved oxygen levels are also thought to play a role in deep-sea gigantism. A 1999 study of benthic
amphipod Amphipoda is an order of malacostracan crustaceans with no carapace and generally with laterally compressed bodies. Amphipods range in size from and are mostly detritivores or scavengers. There are more than 9,900 amphipod species so far descri ...
crustaceans found that maximum potential organism size directly correlates with increased dissolved oxygen levels of deeper waters. The solubility of dissolved oxygen in the oceans is known to increase with depth because of increasing pressure, decreasing salinity levels and temperature. The proposed theory behind this trend is that deep-sea gigantism could be an adaptive trait to combat asphyxiation in ocean waters. Larger organisms are able to intake more dissolved oxygen within the ocean, allowing for sufficient respiration. However, this increased absorption of oxygen runs the risk of toxicity poisoning where an organism can have oxygen levels that are so high that they become harmful and poisonous.


Gallery

File:Giant isopod.jpg, A giant isopod (''Bathynomus giganteus'') may reach up to in length. File:Japanese spider crab.jpg, A
Japanese spider crab The Japanese spider crab (''Macrocheira kaempferi'') is a species of marine crab that lives in the waters around Japan. It has the largest known leg-span of any arthropod. It goes through three main larval stages along with a prezoeal stage to g ...
whose outstretched legs measured across. File:Moroteuthis robusta bronco.jpg, A robust clubhook squid, whose mantle reaches in length, caught off
Alaska Alaska ( ; russian: Аляска, Alyaska; ale, Alax̂sxax̂; ; ems, Alas'kaaq; Yup'ik: ''Alaskaq''; tli, Anáaski) is a state located in the Western United States on the northwest extremity of North America. A semi-exclave of the U.S., ...
. File:Giant Oarfish.jpg, A king of herrings
oarfish Oarfish are huge, greatly elongated, pelagic lampriform fish belonging to the small family Regalecidae. Found in areas spanning from temperate ocean zones to tropical ones, yet rarely seen, the oarfish family contains three species in two gene ...
, caught off California. File:Colossendeis colossea Smithsonian Natural History Museum.jpg, A '' Colossendeis colossea'' sea spider, displayed at the Smithsonian. File:Stygiomedusa Gigantea ov.jpg, A '' Stygiomedusa'' jellyfish, which can grow up to in length. File:Plesiobatis daviesi cochin.jpg, A deepwater stingray, which can reach up to in size.


See also

*
Cephalopod size Cephalopods vary enormously in size. The smallest are only about long and weigh less than at maturity, while the largest—the giant and colossal squids—can exceed in length and weigh close to half a tonne (), making them the largest living ...
*
Dwarfing Dwarfing is a process in which a breed of animals or cultivar of plants is changed to become significantly smaller than standard members of their species. The effect can be induced through human intervention or non-human processes, and can include ...
*
Island gigantism Island gigantism, or insular gigantism, is a biological phenomenon in which the size of an animal species isolated on an island increases dramatically in comparison to its mainland relatives. Island gigantism is one aspect of the more general "i ...
*
Insular dwarfism Insular dwarfism, a form of phyletic dwarfism, is the process and condition of large animals evolving or having a reduced body size when their population's range is limited to a small environment, primarily islands. This natural process is disti ...
*
Largest organisms The largest organisms now found on Earth can be determined according to various aspects of an organism's size, such as: mass, volume, area, length, height, or even genome size. Some organisms group together to form a superorganism (such as ants ...
*
Megafauna In terrestrial zoology, the megafauna (from Greek μέγας ''megas'' "large" and New Latin ''fauna'' "animal life") comprises the large or giant animals of an area, habitat, or geological period, extinct and/or extant. The most common threshold ...


References


External links


Science Daily: Midgets and giants in the deep sea
{{DEFAULTSORT:Deep-Sea Gigantism Animal size Evolutionary biology concepts Marine organisms Ecogeographic rules