Antarctic inverts at risk from predators as temperatures rise


Scientists from the UK and USA have revealed that the unique benthic invertebrate fauna of the Antarctic continental shelf may be the next victims of global warming.

In a paper published in the most recent issue of Annual Review of Ecology, Evolution, and Systematics, Richard Aronson and co-authors review the benthic invertebrate fauna of the Antarctic continental shelf and using examples from the fossil record, review its vulnerability to durophagous (shell crushing predators).

The invertebrate fauna consists largely of softer-bodied organisms such as polychaetes, bryozoans, sponges, pycnogonids, amphipods, and ascidians and harder-shelled organisms such as gastropods and bivalves are conspicuously poorly-represented.

In this respect, the benthic community is of a retrograde nature, being Palaeozoic-type in structure and function and found nowhere else on Earth.

The authors write: A critical feature of benthic ecology in Antarctica is that skeleton-crushing predation (durophagy) is very limited at present. Evolutionarily modern (i.e., post-Paleozoic), durophagous predators"fish and decapods"are largely responsible for structuring food webs in subtidal marine communities at temperate, subtropical, and tropical latitudes.

In contrast, there are no brachyuran crabs, lobsters, sharks, or rays in Antarctica; the diversity and abundance of skates (Rajidae) are low; and the teleostean fauna is dominated by two nondurophagous clades, namely the notothenioids and the liparids.

Weddell seals feed at depth, but their diet consists primarily of free-swimming prey such as fish and squid; although these seals take benthic prey occasionally, there are no marine mammals in Antarctica that are ecologically equivalent to the durophagous, bottom-feeding walruses or gray whales of the Arctic.

So far, the absence of durophagous predators such as crustaceans and elasmobranchs is due largely to the low temperatures of the waters around Antarctica. However, that may change in the future if global ocean temperatures continue to rise.

Rising sea temperatures would remove this temperature constraint on the physiology of durophagous predators (e.g. crustaceans have problems metabolizing magnesium under the low temperatures observed in the Antarctic continental shelf) and facilitate their invasion, with dire effects for the endemic shallow-water benthic communities of Antarctica.

The invasion of the Antarctic continental shelf by durophagous invertebrates is already under way, with the Northern Hemisphere spider crab Hyas araneus being recorded from Antarctic continental waters in 1986.

For more information, see the paper: Aronson, RB, S Thatje, A Clarke, LS Peck, DB Blake, CD Wilga and BA Seibel (2007) Climate change and invasibility of the Antarctic benthos. Annual Review of Ecology, Evolution, and Systematics 38, pp. 129"154.