Antarctic marine explorers reveal biological changes

Once roofed by ice for millennia, a 10.000 square km portion of the Antarctic seabed represents a true frontier, one of Earth's most pristine marine ecosystems, made suddenly accessible to exploration by the collapse of the Larsen A and B ice shelves, 12 and five years ago respectively.

Now it has yielded secrets to some 52 marine explorers who accomplished the seabed's first comprehensive biological survey during a 10-week expedition aboard the German research vessel Polarstern.

The expedition forms part of the Census of Antarctic Marine Life, which has 13 upcoming voyages scheduled during International Polar Year, to be launched in Paris on the 1st of March. A project of the global Census of Marine Life collaboration, CAML is responsible for the synthesis of taxonomic data and supports the efforts of national programs the world over. Leaving South Africa on 23rd of November, the research icebreaker Polarstern operated by the Alfred Wegener Institute for Polar and Marine Research criss-crossed the northwest Weddell Sea. The cruise included the Larsen A and B zones, an area about the size of Jamaica. The voyage ended on 30th of January. With sophisticated sampling and observation gear, including a camera-equipped, remotely-operated vehicle, experts on the Polarstern have returned with revealing photography of life on a seabed uncapped by the disintegration of Larsen A and B. The expedition uncovered a wealth of new insights and brilliant images of unfamiliar creatures among an estimated 1.000 species collected, several of which may prove new to science. The Polarstern's mission included charting the environmental impact of history's largest known ice shelf collapses. Polarstern's team set out to find what indigenous forms of marine life existed under Larsen A and B, and what new organisms now are opportunistically moving in, redefining the ecosystem.

Polarstern discoveries

Larsen zone seafloor sediments were extremely varied, ranging from bedrock to pure mud. As a result, animals living on the sediment (epifauna) were highly varied as well, though far less abundant in the Larsen A and B areas - perhaps only 1% animal abundance compared to sea beds in the eastern part of the Weddell Sea. In the relatively shallow waters of the Larsen zone, scientists were intrigued to find abundant deep sea lilies (members of a group called crinoids) and their relatives, sea cucumbers and sea urchins. These species are more commonly found around 2,000 meters or so, able to adapt to life where resources far more scarce - conditions similar to those under an ice shelf. Apparent newcomers found colonising the Larsen zone include fast-growing, gelatinous sea squirts. The scientists found dense patches of sea squirts and say they were likely able to colonise the Larsen B area only after ice shelf broke in 2002. Very slow-growing animals called glass sponges were discovered, with greatest densities in the Larsen A area, where life forms have had seven more years to re-colonise than Larsen B. The high number of juvenile forms of glass sponges observed probably indicates shifting species composition and abundance in the past 12 years.

Among many hundreds of animal specimens collected on the voyage are 15 potential new amphipod (shrimp-like) species from 400 specimens and 4 presumed new species of cnidarians (organisms related to coral, jelly fish and sea anemones). Extensive analyses will be conducted to prove whether or not candidate specimens are in fact new species. Confirmed new species will be logged in the Census of Marine Life OBIS (Ocean Biogeographic Information System) database and its Antarctic component SCAR-MarBIN (the Marine Biodiversity Information Network). The remotely operated vehicle (ROV) used on Polarstern revealed less scouring damage than anticipated from icebergs that broke away from the Larsen shelves. In shallower depths to about 220 metres, the scientists found considerable richness of species variety.

A potentially far-reaching find by the Polarstern ROV: small clusters of dead clamshells littering an area on the dark ocean floor and pointing to the presence of a very rare 'cold seep' - essentially a sea floor vent spewing methane and sulphide. Seeps can create a temporary habitat for animal life in otherwise barren, inhospitable terrain for many years before extinguishing, abruptly starving off the community.

In all, some 700 and 8.000 nautical miles were dedicated by the Polarstern and its helicopter crews respectively to recording the presence and behaviours of marine mammals, which included Minke whales close to the pack ice edge and very rare beaked whale species near Elephant Island. 'It was surprising how fast such a new habitat was used and colonised by Minke whales in considerable densities,' says Dr Meike Scheidat. 'They indicate that the ecosystem in the water column changed considerably.' Fisheries investigations were carried out at islands west and north of the Antarctic Peninsula. The results of 85 hauls over 19 days show the biomass of two Antarctic cod species has increased since a survey in 2003 while stocks of Blackfin and Mackerel Icefish has decreased. The results will contribute to fish stock monitoring and assessment ongoing under the Convention on the Conservation of Antarctic Marine Living Resources.

Tarik Chekchak, Program Manager of the Cousteau Society, says: 'The Southern Ocean spans 35 million square km - 10% of Earth's ocean surface, and ice shelves cover 1.5 million square km of it. When Captain Cousteau explored Antarctica aboard the Calypso in 1972-73, the Larsen B ice shelf was 3.250 square km bigger and krill abundance in the Peninsula was much higher than today. The annual local temperature has risen 2.5 C since the 1940's. Impacts of these changes on the Southern Ocean ecosystem are substantial. Interplay between ocean circulation, sea ice extent, ice shelf cover and the iceberg's mechanical action on the sea bed seem to determine the characteristics of some key planktonic and benthic communities. In a changing environment, the results of the CAML efforts are key to advancing our ability to understand our biosphere, inform public debate and allow decision-makers to lead us into a more sustainable future.'