Aronson et al. (2009) used the Eocene fossil record in the La Meseta Formation at Seymore Island, Antarctic Peninsula, to track the response of suspension feeding echinoderms and brachiopods that lived off the Antarctic coastal shelf at the time of the Eocene cooling event. The patterns of decline in predation on these organisms within the pre-cooling Eocene ecosystem were then used to predict how the current warming of Antarctic coastal water would affect the current organisms living along the shelf. It is predicted that increasing predation by invasive shell breaking species will reduce current populations of suspension feeding echinoderms possibly into extinction. It is also predicted that climate change will not affect the colonies of brachiopods or the current amount of shell drilling predation on modern populations of bivalves. –Rosemary Kulp
Aronson RB, Moody RM, Ivany LC, Blake DB, Werner JE, Linda C. Ivany4, Daniel B. Blake5, John E. Werner5¤a,
Alexander Glass5 (2009) Climate Change and Trophic Response of the Antarctic Bottom Fauna. PLoS ONE 4(2):e4385. doi:10.1371/journal.pone.0004385
The morphology of the Antarctic fauna is a product of climatic cooling that began in the Eocene 33.5 million years ago. At the beginning of the Eocene the Antarctic climate was considered temperate and contained predators like bony fish (telosts), crustaceans, and sharks (neoslachian elasmobranchs). With the cooling of coastal sea temperatures of up to 10°C by the end of the Eocene period, most of the durophageous (boney fish, ray, shark, and crustacean) predators became extinct. Along with the extinction of these predators, crinoids and ophiuroid (suspension feeders that prey on zooplankton) populations were able to increase. In today’s Antarctic coastal waters, the top predators are slow moving invertebrates that cannot break hard-shelled prey.
Current increases in polar water temperatures allow predators like anomuran crabs to reinvade the western arctic peninsula in deep water only 1–2 degrees warmer than water on the coastal shelf. In order to predict how the current populations will be affected by the possible invasions of shell breaking, shell drilling, and durophageous predators, the Eocene fossil record from Seymore Island, Antarctic Peninsula was used to track the effects of a cooling period on the populations of modern organisms living on the Antarctic shelf and soft substrata.
After comparing the fossil record to modern day data it was found that populations of ophiuroids and crinoids increased after the cooling event but not before. Since both ophiuroids and crinoids are susceptible to predation and unintentional damage by durphageous organisms, their abundance is evidence of low predation after the post cooling Eocene period.
In order to determine whether there was any change in predation by shell breakers on brachiopods across the 41 million year Eocene cooling event, the shell morphologies of Bouchardia antarctica from two different sites in the pre cooling period and two sites in the post cooling period were compared using principle component analysis in order to determine the variance in shell morphology across sites and between the two time intervals. After comparing four shell metrics (i.e. length of brachial valve, and width of brachial valve) that could be measured precisely, it was determined that there was no consistent change in shell shape or size associated with a decrease in temperature or with the decline of predators.
A second examination was done on predation from shell drilling gastropods using a similar method, comparing evidence of shell drilling predation (boreholes) between nests of B. antarctica and between species of bivalve also susceptible to shell drilling predation before and after the cooling event. The data showed that declining temperatures in the Eocene did not significantly affect the frequency of shell drilling predation on the bivalve species while B. antarctica were not affected either before or after the cooling by shell drilling predation.
When running the Eocene cooling event in reverse, it was predicted that increasing predation associated with reinvasion of shell breaking predators would reduce drastically the populations of suspension feeders like epifaunal ophiuroids and crinoids that currently inhabit the area. It was concluded that the epifaunal brachiopods would not decline with the increase of boney fish (durophage) predators. Lastly, it was determined that the intensity of shell drilling predation on infaunal bivalves would not change appreciably.