| Themisto gaudichaudii | |
|---|---|
 | |
Scientific classification  | |
| Kingdom: | Animalia |
| Phylum: | Arthropoda |
| Subphylum: | Crustacea |
| Class: | Malacostraca |
| Superorder: | Peracarida |
| Order: | Amphipoda |
| Suborder: | Hyperiidea |
| Family: | Hyperiidae |
| Genus: | Themisto |
| Species: | T. gaudichaudii |
| Binomial name | |
| Themisto gaudichaudii Guérin-Méneville, 1825 | |
Themisto gaudichaudii is an amphipod crustacean of the suborder Hyperiidea.
The 260 species of hyperiid amphipods are large-eyed and planktonic amphipods, whereas gammarid amphipods have smaller eyes and tend to live on the sea floor. The handful of species of the genus Themisto are the most abundant of all amphipods. Unlike other hyperiids, which parasitise gelatinous animals such as salps and jellyfish, Themisto swims free in the plankton, and is much sleeker and more streamlined than other amphipods. Themisto often forms dense swarms, similar to krill swarms.
Themisto gaudichaudii is a voracious predator of anything smaller than itself, and occasionally of animals its own size or larger. In most places, the most abundant members of the plankton community are copepods, which make up the bulk of the diet of T. gaudichaudii, but it also eats fish larvae, chaetognaths, pteropods, juvenile krill, and anything else it comes across. The long limbs are folded against the body for swimming, and extend to catch prey in a similar way to the praying mantis.
T. gaudichaudii is the Southern Ocean species of the genus, ranging through the Antarctic region and further north onto Southern Hemisphere continental shelves. In many places, it is the most abundant predator in the plankton, and is often the third-most abundant member of the plankton community, after copepods and krill.
T. gaudichaudii is an important prey item for predators such as the macaroni penguin and icefish, as well as many species of seabirds, notably diving petrels.
Adults in the Antarctic are normally 12–21 millimetres (0.47–0.83 in) long, and normally live for a year, although a few may survive to their second year and reach 28 mm (1.1 in) long. Adults off Southern Africa are smaller, reaching 12 mm (0.47 in).
Themisto gaudichaudii was first described by Félix Édouard Guérin-Méneville in 1825. Since the genus was then monotypic, T. gaudichaudii became the type species of the genus Themisto. [1] The type material was collected "sur les côtes des Îles Malouines" (off the coast of the Falkland Islands). [1]
Plankton are the diverse collection of organisms found in water that are unable to propel themselves against a current. The individual organisms constituting plankton are called plankters. In the ocean, they provide a crucial source of food to many small and large aquatic organisms, such as bivalves, fish and whales.
Antarctic krill is a species of krill found in the Antarctic waters of the Southern Ocean. It is the dominant animal species of Earth. It is a small, swimming crustacean that lives in large schools, called swarms, sometimes reaching densities of 10,000–30,000 individual animals per cubic metre. It feeds directly on minute phytoplankton, thereby using the primary production energy that the phytoplankton originally derived from the sun in order to sustain their pelagic life cycle. It grows to a length of 6 centimetres (2.4 in), weighs up to 2 grams (0.071 oz), and can live for up to six years. It is a key species in the Antarctic ecosystem and in terms of biomass, is one of the most abundant animal species on the planet.
Zooplankton are heterotrophic plankton. Plankton are organisms drifting in oceans, seas, and bodies of fresh water. The word zooplankton is derived from the Greek zoon (ζῴον), meaning "animal", and planktos (πλαγκτός), meaning "wanderer" or "drifter". Individual zooplankton are usually microscopic, but some are larger and visible to the naked eye.
Copepods are a group of small crustaceans found in nearly every freshwater and saltwater habitat. Some species are planktonic, some are benthic, a number of species have parasitic phases, and some continental species may live in limnoterrestrial habitats and other wet terrestrial places, such as swamps, under leaf fall in wet forests, bogs, springs, ephemeral ponds, and puddles, damp moss, or water-filled recesses (phytotelmata) of plants such as bromeliads and pitcher plants. Many live underground in marine and freshwater caves, sinkholes, or stream beds. Copepods are sometimes used as biodiversity indicators.
The diving petrels are seabirds in the bird order Procellariiformes. There are five very similar species all in the family Procellariidae and genus Pelecanoides, distinguished only by small differences in the coloration of their plumage, habitat, and bill construction. They are only found in the Southern Hemisphere. Some authorities place the diving petrels in their own family, the Pelecanoididae.[2]
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The crabeater seal, also known as the krill-eater seal, is a true seal with a circumpolar distribution around the coast of Antarctica. They are medium- to large-sized, relatively slender and pale-colored, found primarily on the free-floating pack ice that extends seasonally out from the Antarctic coast, which they use as a platform for resting, mating, social aggregation and accessing their prey. They are by far the most abundant seal species in the world. While population estimates are uncertain, there are at least 7 million and possibly as many as 75 million individuals. This success of this species is due to its specialized predation on the abundant Antarctic krill of the Southern Ocean, for which it has uniquely adapted, sieve-like tooth structure. Indeed, its scientific name, translated as "lobe-toothed (lobodon) crab eater (carcinophaga)", refers specifically to the finely lobed teeth adapted to filtering their small crustacean prey. Despite its name, crabeater seals do not eat crabs. As well as being an important krill predator, the crabeater seal's pups are an important component of the diet of leopard seals, which are responsible for 80% of all crabeater pups deaths.
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Filter feeders are a sub-group of suspension feeding animals that feed by straining suspended matter and food particles from water, typically by passing the water over a specialized filtering structure. Some animals that use this method of feeding are clams, krill, sponges, baleen whales, and many fish. Some birds, such as flamingos and certain species of duck, are also filter feeders. Filter feeders can play an important role in clarifying water, and are therefore considered ecosystem engineers. They are also important in bioaccumulation and, as a result, as indicator organisms.
Calanoida is an order of copepods, a group of arthropods commonly found as zooplankton. The order includes around 46 families with about 1800 species of both marine and freshwater copepods between them. Calanoid copepods are the dominant animals in the plankton in many parts of the world's oceans, making up 55%–95% of plankton samples. They are therefore important in many food webs, taking in energy from phytoplankton and algae and 'repackaging' it for consumption by higher trophic level predators. Many commercial fish are dependent on calanoid copepods for diet in either their larval or adult forms. Baleen whales such as bowhead whales, sei whales, right whales and fin whales rely substantially on calanoid copepods as a food source.
The Hyperiidea are a suborder of amphipods, small aquatic crustaceans. Unlike the other suborders of Amphipoda, hyperiids are exclusively marine and do not occur in fresh water. Hyperiids are distinguished by their large eyes and planktonic habitat. Most species of hyperiids are parasites or predators of salps and jellyfish in the plankton, although Themisto gaudichaudii and a few relatives are free-swimming predators of copepods and other small planktonic animals.
King-of-the-salmon, Trachipterus altivelis, is a species of ribbonfish in the family Trachipteridae. Its common name comes from the legends of the Makah people west of the Strait of Juan de Fuca, which hold that this fish leads the salmon annually to their spawning grounds. Catching or eating king-of-the-salmon was forbidden, as it was feared killing one would stop the salmon run. This myth is reflected by a former specific epithet used for this fish, rex-salmonorum, rex being Latin for "king". The king-of-the-salmon is found in the eastern Pacific Ocean from Alaska to Chile. It is usually found in the open ocean to a depth of 900 meters, though adults sometimes feed on the sea bottom.
Diel vertical migration (DVM), also known as diurnal vertical migration, is a pattern of movement used by some organisms, such as copepods, living in the ocean and in lakes. The migration occurs when organisms move up to the uppermost layer of the sea at night and return to the bottom of the daylight zone of the oceans or to the dense, bottom layer of lakes during the day. The word diel comes from the Latin dies day, and means a 24-hour period. In terms of biomass, it is the greatest migration in the world. It is not restricted to any one taxon as examples are known from crustaceans (copepods), molluscs (squid), and ray-finned fishes (trout). Various stimuli are responsible for this phenomenon, the most prominent being response to changes in light intensity, though evidence suggests that biological clocks are an underlying stimulus as well. The phenomenon may arise for a number of reasons, though it is most typically to access food and avoid predators. While this mass migration is generally nocturnal, with the animals ascending from the depths at nightfall and descending at sunrise, the timing can be altered in response to the different cues and stimuli that trigger it. Some unusual events impact vertical migration: DVM is absent during the midnight sun in Arctic regions and vertical migration can occur suddenly during a solar eclipse.
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Crustaceans may pass through a number of larval and immature stages between hatching from their eggs and reaching their adult form. Each of the stages is separated by a moult, in which the hard exoskeleton is shed to allow the animal to grow. The larvae of crustaceans often bear little resemblance to the adult, and there are still cases where it is not known what larvae will grow into what adults. This is especially true of crustaceans which live as benthic adults, more-so than where the larvae are planktonic, and thereby easily caught.
Mertensia ovum, also known as the Arctic comb jelly or sea nut, is a cydippid comb jelly or ctenophore first described as Beroe ovum by Johan Christian Fabricius in 1780. Unusually among ctenophores, which normally prefer warmer waters, it is found in the Arctic and adjacent polar seas, mostly in surface waters down to 50 metres (160 ft).
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Themisto is a genus of marine amphipods in the family Hyperiidae. Their distribution is cosmopolitan.
Gonatopsis borealis, the Boreopacific armhook squid, is a species of squid from the North Pacific Ocean. It is a member of the family Gonatidae. It is an abundant species which is currently caught mainly as a bycatch by fishing boats targeting other quarry. It is an important prey species for many commercially important species of fish, as well as for marine mammals.