Discovery Magazine

Photo Credit: R. Aronson and J. McClintock

Climate Change and Predatory Invasion of the Antarctic Benthos

Climate change in Antarctica is altering marine ecosystems through rising temperatures and ocean acidification. Marine communities in Antarctica face an additional threat: climatically driven biological invasions. Large populations of durophagous (skeleton-breaking) king crabs, Paralomis birsteini (Lithodidae), have recently been discovered on the continental slope off Marguerite Bay, western Antarctic Peninsula (WAP). As sea temperatures off the WAP warm over the next several decades, these generalist shell-crushers will likely expand their habitat range to the continental shelf. The establishment of viable populations of Paralomis on the shelf could spell disaster for the endemic fauna and its unique trophic structure. Because the marine environment surrounding Antarctica remains largely unexplored, the extent and viability of lithodid populations on the slope are poorly known. This study will assess the status of Paralomis populations on the slope off the WAP and their potential to disrupt benthic communities on the continental shelf.

The shelf fauna of Antarctica currently lacks the durophagous predators that structure benthic food webs in nearshore habitats elsewhere. Climate change in Antarctica beginning 41 million years ago in the Eocene, specifically a short interval of rapid cooling, eliminated durophagous fish and crustaceans from Antarctic waters. Since then, the benthos has evolved toward an archaic, quasi-Paleozoic community structure in the absence of top predators. The rapid reversal of Eocene climate change in Antarctica--the recent trend of rising sea temperatures off the WAP--are now drawing down the physiological barriers to predators.The return of crabs to the Antarctic shelf could re-modernize the benthic fauna and homogenize it with marine faunas elsewhere. The potential and consequences of such an invasion will be assessed off Marguerite Bay by employing two approaches: (1) high-resolution photography of the bottom faunas; and (2) determination of the health, viability, and diet of the Paralomis population.

In the first approach, a towed underwater vehicle will be used to image the bottom fauna along transects arranged in a stratified-random design, providing density estimates of Paralomis and other macrofauna on the continental shelf, slope, and rise. Macrofauna associated with crab populations will be compared quantitatively to macrofauna in crab-free areas at the same depths to determine the current impact of the crabs and which types of hard-shelled invertebrates on the shelf will be most vulnerable to increased predation pressure. Spatial analysis will be used to characterize the patch structure of Paralomis. The second approach will involve trapping Paralomis in deep water. Data on gender, morphometrics, molting state, fecundity, parasite load and gut contents will be collected for each crab. The information will be compared to available data for conspecific and congeneric king-crab stocks at lower latitudes to determine: (1) the potential for Paralomis to expand from the slope into the incrementally harsher environment of the shelf; and (2) whether the crabs are eating invertebrates with which they are negatively associated in the photographic transects. The data will allow us to generate predictions about the types and rates of biotic responses to climate change in Antarctica.