Prospects for survival in the Southern Ocean: vulnerability of benthic species to temperature change
Organisms have a limited number of responses that enhance survival in changing environments. They can: 1. Cope within existing physiological flexibility; 2. Adapt to changing conditions; or 3. Migrate to sites that allow survival. Species inhabiting coastal seabed sites around Antarctica have poorer physiological capacities to deal with change than species elsewhere. They die when temperatures are raised by only 5–10°C above the annual average, and many species lose the ability to perform essential functions, e.g. swimming in scallops or burying in infaunal bivalve molluscs when temperatures are raised only 2–3°C. The ability to adapt, or evolve new characters to changing conditions depends, at least in part, on generation time. Antarctic benthic species grow slowly and develop at rates often x5–x10 slower than similar temperate species. They also live to great age, and exhibit deferred maturity. Longer generation times reduce the opportunities to produce novel mutations, and result in poorer capacities to adapt to change. Intrinsic capacities to colonize new sites and migrate away from deteriorating conditions depend on adult abilities to locomote over large distances, or for reproductive stages to drift for extended periods. The slow development of Antarctic benthic species means their larvae do spend extended periods in the water column. However, whereas most continents have coastlines extending over a wide range of latitude, Antarctica is almost circular in outline, is isolated from other oceans by the circumpolar current, and its coastline covers few degrees of latitude. Thus in a warming environment there are fewer places to migrate to. On all three major criteria Antarctic benthic species appear less capable than species elsewhere of responding to change in ways that can enhance survival.