SMUGGLER'S COVE REVISITED: LONG-TERM CHANGES IN TIME-AVERAGED SUBFOSSIL MOLLUSCAN ASSEMBLAGES

Previous investigations of modern, subfossil marine assemblages suggest that these assemblages tend to reflect faithfully the preservable elements of the living communities from which they were derived. It has also been shown that, because of time-averaging, dynamic transitions in subenvironments, which occur during the period of accumulation, may be subsumed in the assemblage. The key to determining the degree of influence of time-averaging is to assess changes among subfossil assemblages over a known, extended, interval of time. However, most previous studies of modern, subfossil remains have been constrained by narrow time frames, precluding this type of assessment. In this investigation, a transect in Smuggler’s Cove, St. Croix, U.S. Virgin Islands, sampled previously by Miller (1979-80), was revisited to determine the extent of change over more than two decades among subenvironments and subfossil molluscan remains arrayed along what was previously a gradient of decreasing seagrass cover. During the intervening period, the study area has been subjected to several storms, potentially leading to significant changes in the positions of seafloor zones covered by the three main species of seagrass, potentially effecting changes in the local compositions of subfossil assemblages.

The original, 360 m transect of Miller was reestablished approximately and evaluated at 30 m lateral intervals using airlifting to sample the accumulated subfossil molluscan biota and census methods to assess benthic vegetation cover. Currently, the airlifted samples are being processed to produce a data matrix for multivariate analyses, the results of which will be compared directly to those from Miller’s earlier study. Preliminary results from assessment of benthic vegetation cover indicate that dense Thalassia continues to dominate the southernmost—and shallowest—third of the transect, as it did during the original study. However, there appears to have been a reduction in patchiness for all three seagrasses among more distal zones of the transect. Whether this has any tangible effect on the compositions of subfossil assemblages remains to be seen and will be discussed in the presentation.