QUANTIFYING TAPHONOMIC BIAS IN MOLLUSCAN DEATH ASSEMBLAGES FROM THE CHESAPEAKE BAY: PATTERNS OF LIVE-DEAD FIDELITY AND SHELL DAMAGE

Years of over-fishing, combined with increased nutrient pollution, have had a catastrophic effect on the ecology of the Chesapeake Bay. The Holocene record of Bay mollusks may provide a baseline for ecological restoration, but the effects of taphonomic bias on these assemblages must first be assessed. In this study, we carried out a live-dead assemblage comparison on six sites distributed in the main channel of the Bay. Questions addressed include: (1) how well do death assemblages record the species composition, richness, and abundance of live communities? (2) what forms of shell damage occur in molluscan death assemblages? and (3) does damage differ according to shell mineralogy, life habit, or geographic location? Death assemblage data were obtained from replicate samples, which were collected by box core, sieved into four fractions, and stored temporarily in formalin. Whole specimens and fragments were sorted, identified to species level, and assigned taphonomic damage states. Data on the following taphonomic variables were collected: (1) bioerosion, (2) encrustation, (3) periostracum loss, (4) predatory drilling, (5) disarticulation, (6) fragmentation, (7) fine-scale alteration, (8) and edge-modification. Type of bioeroder, encruster, and/or driller was also noted. Data on live communities at the same sites, sampled over the past twenty years, were provided by the benthic monitoring division of the Chesapeake Bay program. Preliminary results indicate that 83% of the species in the live community were also found in the death assemblage and 90% of the individuals of species found in the death assemblage were also found in the live community. The most prevalent forms of shell damage were periostracum loss, disarticulation, fragmentation, edge-modification, and fine-scale alteration; however, damage did not differ according to mineralogy or life habit. These results are preliminary, but they do suggest that Holocene molluscan assemblages may provide useful estimates of diversity and abundance for ecological restoration of the Chesapeake Bay.