PRESERVATIONAL BIAS AND HISTORICAL ECOLOGY OF HOLOCENE MOLLUSKS IN THE CHESAPEAKE BAY

As ecologists develop solutions to the many problems facing the Chesapeake Bay, the Holocene record of the bay is increasingly used for paleoenvironmental and paleoclimate reconstruction. Despite the potential biases associated with preservation, few of these studies have explicitly taken taphonomy into account. Here, I summarize recent work quantifying preservational bias and exploring the historical ecology of the Holocene record of Chesapeake Bay mollusks.

One important metric of preservational bias is the degree to which Holocene assemblages reflect their source communities (i.e., fidelity). Compositional fidelity can be assessed using live-dead comparisons, in which live communities are sampled and compared with death assemblages. A live-dead comparison on molluscan assemblages from four sites located in the main channel of the upper Chesapeake Bay was performed. A total of 3911 mollusk specimens was obtained from box-core sampling of the death assemblage. The extent to which death assemblages reflect long-term changes in the live community was assessed using live census data (23,466 molluscan specimens) collected by the Chesapeake Bay Program at the same sites. 77% of the species in the live community were found in the death assemblage, and 99% of the individuals of species found in the death assemblage were found in the live community. A strong correlation was also documented between rank abundance of taxa in the death assemblage and live community.

To track molluscan diversity throughout the Holocene, samples were collected from two USGS cores (Kent Island MD03-2661 and Parker Creek MD99-2208). Bulk samples of mollusks were collected from multiple core depths, yielding a total of 33 species and 3410 individuals. In both cores, species richness is elevated in the early Holocene, although this trend is not significant. Species with somewhat higher salinity tolerances were statistically significantly more abundant in the early Holocene. These results are preliminary, but they suggest that: (1) it is possible to use the Holocene record of the Chesapeake Bay as a baseline for ecological restoration and (2) Holocene molluscan assemblages seem to reflect paleoenvironmental changes, despite the low temporal resolution of this record.