Gardens under the ice.
Locked away under the Antarctic sea ice is a rarely seen underwater world teeming with life and colour. The diversity of form and hue in these seabed communities is in stark contrast to the sparse plant and animal communities found on land in Antarctica. Despite our perceptions that the Southern Ocean is a harsh environment, conditions in the sea around the coast of Antarctica are remarkably constant, so although it is cold, with an average temperature only a few tenths of a degree above the freezing point of seawater (-1.85°C), the environment is predictable and hence quite benign for those life forms that have evolved to live there.
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A: Giant hexactinellid sponges such as this take years to grow up to this size and are found in shallow waters only in the Antarctic; elsewhere they are confined to the deep ocean. B: The strange sphere in the centre is another form of sponge. It feeds by filtering particles from the surrounding water. C: This yellow sponge is superficially very similar to one found on tropical reefs in Australia. D: The sea-urchin Sterechinus nuemayeri (centre) is thought to carry around bits of sponge and seaweed to protect it from predation by anemones. E: Sponges can become the home for other species such as the pink starfish on the right. The tufts sticking out to the side are glass-like strands of silicate that form the skeleton of hexactinellid sponges. F: Even the muddy areas are full of life. The brittle star in the centre feeds by sorting through the sediment. G: Every available space on this rock is occupied. H: In shallow areas the sea ice grinds everything off the rocks except a few small species such as tube worms, bryozoans and encrusting red algae that can live in protected crevices. I: The starfish in the centre feeds by engulfing its prey; it then everts its stomach and digests the meal externally.
The shallow sea floor communities of Antarctica have been studied in detail in only a few locations, mainly on the Antarctic Peninsula to the north and in the southern part of the Ross Sea at McMurdo Sound. Neither is representative of the great majority of the coastline of continental Antarctica. Despite the enormous size of Antarctica there are surprisingly few places where shallow waters are accessible for study. They are only found adjacent to the small ice-free areas which make up less than 0.4% of Antarctica, because elsewhere, as the ice of the plateau meets the sea, the seabed is scoured to great depths.
At Casey these sea bed communities are being studied by the Human Impacts Program because they are the best indicator of environmental impacts from abandoned waste disposal sites. In contrast to the rich natural communities found at other locations, the seabed adjacent to the Old Casey tip in Thala Valley is littered with rubbish and supports very few species. These communities will be monitored during clean-up to ensure that the effort invested in removing the tips results in real environmental improvements and a return to natural conditions.
Martin Riddle,
Human Impacts Program Leader, AAD
