Cold, dark and deep. The bottom of the Antarctic sea floor is a mysterious world, teeming with some of the weirdest creatures you’ve ever seen. The Aurora Australis visited one of the world’s most extreme places in the austral summer of 2009 and 2010. Floating more than a kilometre above the sea floor, with the sun shining brightly in the middle of the night, scientists lowered nets and cameras to capture life in the icy depths.
Benthic invertebrates or ‘benthos’ refers to those organisms living on or above the seafloor of our oceans worldwide. In the deepest parts of our oceans, these animals are often adapted for life in extreme environments, where there’s no light, intense cold and huge amounts of pressure from hundreds if not thousands of metres of water above. Getting a glimpse of this weird undersea world requires some special equipment, like cameras mounted in special pressure-resistant housings and strong nets that are dragged along the sea floor to collect wildlife samples.
Tubs of sea life are hauled into labs on board to sort, classify, weigh and identify. Intact specimens are photographed to capture their natural colours and appearance then stored in jars of ethanol or formalin. Thousands of jars are returned to the Australian Antarctic Division’s collection for genetic and taxonomic analysis, both within the Division and by partnering institutions.
As part of National Science Week 2010, the Division’s public display area featured fascinating images of some of these benthic invertebrates. This work was funded by the Fisheries Research and Development Corporation.
Molluscs
Molluscs have a more varied form than any other phylum, and is the largest marine phylum, comprising about 23% of all named marine organisms. Numerous molluscs also live in freshwater and terrestrial habitats. The molluscs found on this voyage range from chitons, snails and sea slugs to octopus.
Antarctic octopus venom is particularly interesting as it is adapted to work in sub zero temperatures. In the future, understanding the structure and the way the venom works may help design drugs for conditions like pain management, allergies and cancer.
Nudibranchs (meaning ‘naked gills’) are soft bodied marine molluscs, also called sea slugs. There are more than 3000 species of nudibranchs, which are renowned for being colourful and attractive. They use chemical sensors on their head to ‘smell’ or ‘taste’ chemicals in the water to find food or other members of their species. All nudibranchs are carnivores. They feed on other invertebrates such as sponges, soft corals and anemones.
Crustacea
The crustaceans are a large group of arthropods which include familiar creatures like lobsters, krill, crabs, isopods and barnacles. They are like insects, which also have an exoskeleton, but differ in usually having many pairs of legs, instead of three pairs.
Prawns and shrimp are superficially similar members of the order Decapoda. The female hump-backed shrimp pictured above has a brood of green eggs attached to swimmerettes beneath her abdomen.
Amphipods are the crustacea most frequently found in the Southern Ocean. The name amphipoda means ‘different footed’ and refers to the different forms of their legs — they have seven pairs of walking legs, with the first four reaching forward and the fifth to seventh reaching backwards. Amphipods range in size from 1 to 340mm. Most amphipods are ‘detritivores’ or scavengers, feeding on dead or decomposing organic matter with their front two pairs of legs. As they moult in order to grow, some species develop heavy armature as they get older.
Pycnogonids
Pycnogonids, or sea spiders, are a widely distributed and diverse group. They occur in tropical, temperate and polar oceans, from shallow water to abyssal depths. They range in size from 1mm to over 70cm in leg span, commonly growing very large in Antarctic waters. About 20% of the world’s known species are found in Antarctica. Sea spiders are carnivores. They have a straw-like proboscis that they insert into animals like hydroids, bryozoans and sponges to suck out their juices.
Echinoderms
Echinoderms like sea stars, feather stars and sea urchins have five-part radial symmetry and move with adhesive tube feet. Their body wall contains an endoskeleton which usually has a spiny surface, hence the Phylum name Echinodermata which means ‘spiny skin’.
Sea lilies live attached to the sea floor. Feather stars consist of a mass of feather-like arms attached to a tiny body, with an upwards facing ‘mouth’. To move about, they move their arms in an organised fashion and rise in the water column, moving a few meters before dropping like a parachute. Video taken on the sea floor often shows Antarctic feather stars swimming as a flight reflex when confronted with the approaching camera.
Bryozoans
Bryozoans are tiny colonial animals. Each animal is independent of the colony and usually no bigger than 1mm. They generally build stony skeletons of calcium carbonate and may grow in a variety of shapes and patterns including lacy fans, branching twigs or mounds.
Bryozoans can often be mistaken for corals, sponges and algae, due to their superficial similarities.
Cnidarians
Cnidarians are very important in the polar benthic environment as they provide structure to the benthic habitat.
The group is united by the presence of cnidocysts, specialised stinging cells which they use to catch prey and defend themselves from predators. Well known members of the group include the stony corals, soft corals and sea anemones.
Soft corals and sea anemones are common in Antarctic waters.
Annelids
Annelids are segmented worms.
Polychaetes, or bristle worms, are the most well-known of Antarctic annelids. They can grow very large in cold Antarctic waters.
