Climate Change and Trophic Response of the Antarctic Bottom Fauna

BACKGROUND: As 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 FINDINGS: We 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 approximately 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, approximately 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/SIGNIFICANCE: Rapid 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

Terrestrial and marine floral response to latest Eocene and Oligocene events on the Antarctic Peninsula

© 2018, © 2018 AASP – The Palynological Society. Palynological results from opposite sides of the northernmost Antarctic Peninsula provide insight on terrestrial vegetation and sea-surface conditions immediately before the Eocene–Oligocene transition (EOT), through Early Oligocene glacial conditions and the subsequent Late Oligocene interglacial interval. A latest Eocene sample set from the uppermost La Meseta Formation on Seymour Island, James Ross (back-arc) Basin, records a low-diversity Nothofagus (southern beech)-dominated vegetation with some podocarp conifers similar to Valdivian-type forest found today in Chile and Argentina. Marine organic-walled phytoplankton include leiospheres and Eocene dinoflagellate cysts such as Vozzhennikovia rotunda, V. apertura, Senegalinium asymmetricum and Spinidinium macmurdoense. Immediately before the EOT near the top of the section the decrease in terrestrial palynomorphs, increase in reworked specimens, disappearance of key dinocysts, and overwhelming numbers of sea-ice-indicative leiospheres plus the small dinoflagellate cyst Impletosphaeridium signal the onset of glacial conditions in a subpolar climate. Early to Late Oligocene samples from the Polonez Cove and Boy Point formations on King George Island, South Shetland Islands (magmatic arc), yielded an extremely depauperate terrestrial flora, likely resulting in part from poor vegetation cover during the Polonez Glaciation but also because of destruction of vegetation due to continued regional volcanism. The prevalence of sea-ice-indicative leiospheres in the marine palynomorph component is consistent with polar to subpolar conditions during and following the Polonez Glaciation