PHYSICAL CONTROLS ON CORAL COMMUNITIES ON THE GEORGE V LAND SLOPE: SOME WORKING HYPOTHESES

Dense coral-sponge communities on the upper continental slope off George V Land have been identified as a Vulnerable Marine Ecosystem in the Antarctic. The challenge is now to understand their likely distribution. The CEAMARC survey of 2007/2008 found these communities at sites on the upper slope in depths of 570 – 950 m. Based on these results we propose some working hypotheses to explain their distribution. Icebergs scour to 500 m in this region and the lack of such disturbance is probably a factor allowing growth of rich benthic ecosystems. In addition, the richest communities are found in the heads of canyons. We suggest two possible oceanographic mechanisms linking abundant filter feeder communities and canyon heads. The canyons in which they occur receive descending plumes of Antarctic Bottom Water formed on the George V shelf and these water masses could entrain abundant food for the benthos. Maps of water properties measured during the Collaborative East Antarctic Marine Census (CEAMARC) survey provide some support for this idea. Another possibility is that the canyons harbouring rich benthos are those that cut the shelf break. Such canyons are known sites of high productivity in other areas because of a number of oceanographic factors, including strong current flow and increased mixing, and the abrupt, complex topography. These hypotheses provide a framework for the identification of areas where there is a higher likelihood of encountering these Vulnerable Marine Ecosystems.