Global climate change and the origin of modern benthic communities in Antarctica

Marine benthic communities living in shallow-water habitats (< 100 m depth) in Antarctica possess characteristics reminiscent of Paleozoic marine comm unities and modern deep-sea communities. The absence of crabs and sharks, t he limited diversity of teleosts and skates, the dominance of slow-moving i nvertebrates at higher trophic levels, and the occurrence of dense ophiuroi d and crinoid populations indicate that skeleton-breaking predation is limi ted in Antarctica today, as it was worldwide during the Paleozoic and as it is in the deep sea today. The community structure of the antarctic benthos has its evolutionary roots in the Eocene. Data from fossil assemblages at Seymour Island, Antarctic Peninsula suggest that shallow-water communities were similar to communities at lower latitudes until they were affected by global cooling, which accelerated in the late Eocene to early Oligocene. Th at long-term cooling trend ultimately resulted in the polar climate and pec uliar community structure found in Antarctica today. Declining temperatures beginning late In the Eocene are associated with the disappearance of crab s, sharks, and most teleosts. The sudden drop in predation pressure allowed dense ophiuroid and crinoid populations to appear and flourish. These late Eocene echinoderm populations exhibit low frequencies of sublethal damage (regenerating arms), demonstrating that there was little or no predation fr om skeleton-breaking fish and decapods. Current scenarios of global climate change include predictions of increased upwelling and consequent cooling i n temperate and subtropical upwelling zones. Limited ecological evidence su ggests that such cooling could disrupt trophic relationships and favor retr ograde community structures in those local areas.