Research Objectives:
Global climate change in the late Eocene had an important influence in Antarctica. This was the beginning of the transition from a cool-temperate climate to the current one. The cooling trend strongly influenced the structure of shallow-water and antarctic marine communities, and these effects are evident in the ecological relationships among modern species. Cooling reduced the abundance of fish and crabs, which in turn reduced skeleton-crushing predation on invertebrates. Reduced predation allowed dense populations of ophiuroids (brittlestars) and crinoids (sea lilies) to appear in shallow-water settings at the end of the Eocene. These low-predation communities appear as dense fossil echinoderm assemblages in the La Meseta Formation on Seymour Island.
Today, dense ophiuroid and crinoid populations are common in the shallow waters of Antarctica but have generally disappeared from similar habitats at temperate and tropical latitudes. Although the influence of declining predation on antarctic ophiuroids and crinoids is well documented, the effects of cooling on the more abundant mollusks have not been investigated. We will therefore examine the evolutionary ecology of gastropods (snails) and bivalves (clams) in the late Eocene.
We will test a series of hypotheses based on the predicted responses of mollusks to declining temperature and changing levels of predation:
+ First, defensive features of gastropod shells, such as spines and ribbing, should decline as the temperature and, therefore, the activity of skeleton-crushing predators declined.
+ Second, drilling of bivalve prey by predatory gastropods should increase, since the drillers should themselves have been subject to less predation as the temperature declined. Drilled shells should become more common.
+ Third, patterns in the thickness of shells will make it possible to separate the direct physiological effects of temperature (shells are harder to produce at cooler temperatures and so should be thinner) from the indirect effects of temperature (increased drilling predation should result in thicker shells).
Seymour Island contains the only readily accessible fossil outcrops from this crucial period in Antarctica. Global climate change will probably increase upwelling in some temperate coastal regions. Evidence suggests that the resulting decline in sea temperatures could lower predation in those areas. Understanding the response of the La Meseta fauna to cooling in the late Eocene will provide direct insight into the rapidly changing structure of modern benthic communities.
