Abstract
BackgroundAs Earth warms, temperate and subpolar marine species will increasingly shift their geographic ranges poleward. The endemic shelf fauna of Antarctica is especially vulnerable to climate-mediated biological invasions because cold temperatures currently exclude the durophagous (shell-breaking) predators that structure shallow-benthic communities elsewhere.Methodology/Principal FindingsWe used the Eocene fossil record from Seymour Island, Antarctic Peninsula, to project specifically how global warming will reorganize the nearshore benthos of Antarctica. A long-term cooling trend, which began with a sharp temperature drop ∼41 Ma (million years ago), eliminated durophagous predators—teleosts (modern bony fish), decapod crustaceans (crabs and lobsters) and almost all neoselachian elasmobranchs (modern sharks and rays)—from Antarctic nearshore waters after the Eocene. Even prior to those extinctions, durophagous predators became less active as coastal sea temperatures declined from 41 Ma to the end of the Eocene, ∼33.5 Ma. In response, dense populations of suspension-feeding ophiuroids and crinoids abruptly appeared. Dense aggregations of brachiopods transcended the cooling event with no apparent change in predation pressure, nor were there changes in the frequency of shell-drilling predation on venerid bivalves.Conclusions/SignificanceRapid warming in the Southern Ocean is now removing the physiological barriers to shell-breaking predators, and crabs are returning to the Antarctic Peninsula. Over the coming decades to centuries, we predict a rapid reversal of the Eocene trends. Increasing predation will reduce or eliminate extant dense populations of suspension-feeding echinoderms from nearshore habitats along the Peninsula while brachiopods will continue to form large populations, and the intensity of shell-drilling predation on infaunal bivalves will not change appreciably. In time the ecological effects of global warming could spread to other portions of the Antarctic coast. The differential responses of faunal components will reduce the endemic character of Antarctic subtidal communities, homogenizing them with nearshore communities at lower latitudes.
Highlights
Polar marine organisms are physiologically adapted to coldwater conditions
Echinoderms and Brachiopods The stratigraphic distribution of autochthonous concentrations of articulated fossil echinoderms in the nearshore, shallow-marine facies that comprise the Eocene La Meseta Formation at Seymour Island shows that dense populations of ophiuroids (Ophiura hendleri) and crinoids flourished on soft substrata after the 41-Ma cooling event, but not before (Fig. 1; Table 1)
Sea-surface temperatures off the western Antarctic Peninsula (WAP) have risen by 1uC in the last 50 years, making that area one of the fastest-warming regions of the World Ocean [34]
Summary
Polar marine organisms are physiologically adapted to coldwater conditions. Being cold-stenothermal places them at great risk from the direct effects of global warming [1]. The endemic character of the Antarctic nearshore fauna and its uniquely truncated trophic structure [5,6,7] are products of climatic cooling that began in the Eocene and led to the growth of an ice sheet on Antarctica at the Eocene–Oligocene boundary ,33.5 Ma (million years ago) [8,9]. Durophagous predators persisted in Antarctica until at least the end of the Eocene, but they were far less active after 41 Ma [2,11]. They became extinct as temperatures declined further, the timing of those post-Eocene extinctions is uncertain. The endemic shelf fauna of Antarctica is especially vulnerable to climate-mediated biological invasions because cold temperatures currently exclude the durophagous (shell-breaking) predators that structure shallow-benthic communities elsewhere
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