THE PRESERVATION POTENTIAL OF METER-SCALE PATCHINESS IN MARINE FAUNAL ASSEMBLAGES: UNDERSTANDING THE SPATIAL VARIABILITY OF MOLLUSKS AT DIM BAY, SAN SALVADOR, BAHAMAS

The extent to which the spatial variability of faunal assemblages is preservable in the fossil record is a question that has long interested paleoecologists. Both modern and fossilized faunal assemblages are spatially variable, but the degree to which the spatial variation in fossil assemblages reflects it’s original (life) variability in not well understood. Numerous studies have attempted to address this type of question at regional scales. In contrast, we were interested in addressing this question at very fine spatial scales (meters to tens of meters). To do this, we examined modern mollusk death assemblages in sediment from Dim Bay, Bahamas as a modern analog for a fossil assemblage.

Dim Bay is located on the southeast side of the island of San Salvador in the Bahamian archipelago, and represents a relatively high-energy carbonate marine system. It is ideal for this study because it has both areas of open sand and numerous patchreefs. We sampled along a 60 meter transect at 10 meter intervals. Many mollusk species will only live on patchreefs in life, however, dead shells from the patchreef will accumulate in the open sand. If the mollusk death assemblages are random in relation to their distance from a patchreef, then the spatial variability of the death assemblage is not a reflection of the life assemblage. If, however, there is a patchreef “signal”, with more patchreef fauna present in samples closer to patchreefs, then small-scale spatial patchiness might be preservable.

We found that although the samples were variable in their mollusk faunal assemblages, there was not a strong signal for patchreef proximity. This indicates that small-scale spatial patchiness on the order of meters to tens of meters might not be reflected in the fossil record for depositional environments similar to Dim Bay. These results are important because they not only allow paleontologists to better understand how well spatial patchiness might be preserved, but also because they could help inform the appropriate sampling protocol for paleontological studies attempting to capture local diversity using fossils. If death assemblages are not strongly influenced by fine scale habitat patchiness, than samples might be more accurately reflecting wider scale diversity patterns, rather than localized fluctuations.