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Degree

MS, University of Cincinnati, Arts & Sciences : Geology, 2003.

Abstract

To better understand the processes that produce time-averaged fossil assemblages, paleontologists have long investigated the formation of subfossil assemblages on modern seafloors. Generally, it has been demonstrated that these assemblages faithfully reflect the living assemblages and benthic environments from which they were derived. Nevertheless, they may typically contain skeletal material that is hundreds to thousands of years old, and few researchers have considered how subfossil assemblages change over time in response to environmental transitions that alter life assemblages. In this investigation, I evaluate the degree of temporal stability among subfossil molluscan assemblages over a span of some two decades in Smuggler’s Cove, St. Croix, US Virgin Islands. A transect sampled initially by Miller in 1979-1980 was reestablished approximately and resampled during 2002. The transect paralleled a gradient of decreasing seagrass cover and increasing bioturbation by the decapod crustacean Callianassa. Subfossil molluscan samples and benthic vegetation counts were taken at 30 m lateral intervals for direct comparison with data from Miller’s study. Results demonstrate that, after 22 years, species richness and composition of subfossil molluscan communities continue to reflect the fundamental environmental gradient, characterized by a transition from herbivorous gastropods and lucinid bivalves in seagrass beds to actively burrowing bivalves and predatory gastropods in bioturbated zones containing less seagrass. However, the abundance of key taxa changed significantly along the transect during the intervening period; these differences can be recognized in both the subfossil and living assemblages. Most notably, there was a significant decline throughout the study area of the previously ubiquitous grazing gastropod, Cerithium litteratum, and an increase in the abundance of another grazing gastropod, Tricolia affinis. These results indicate that subfossil assemblages are highly dynamic and continue to incorporate changes in the life assemblage until the moment of isolation from surficial sedimentary processes. The fidelity to life assemblages of time-averaged subfossil assemblages clearly depends on the ability of the subfossil assemblages to keep pace with changes in the composition of the live fauna.

Subject Headings

Paleontology ; Paleoecology

Keywords

subfossil assemblage; seagrass; Smuggler's Cove; cerithium; tricolia

Advisor

Dr. Arnold I. Miller

Pages

134p.

Document number: ucin1070394498
Permalink: http://rave.ohiolink.edu/etdc/view?acc_num=ucin1070394498

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