The influence of environmental gradients on molluscan diversity, community structure, body size, and predation in a carbonate tidal creek, San Salvador (The Bahamas)

Abstract

The ecosystem at Pigeon Creek in San Salvador, the Bahamas, provides a unique opportunity for the analysis of complex modern biological processes and how they operate within spatial and chemical gradients in order to assess the stratigraphic scale of the incipient fossil record. This study considers the influence of environmental factors upon molluscan diversity, body size, and predator-prey interactions in order to assess the role that gradients may play at a single horizon. Samples were collected from 26 different localities within a carbonate intertidal creek, Pigeon Creek. Molluscan samples were identified to species level, measured for specimen length and width, presence of a drill hole, and drill diameter, and ordinated using canonical correspondence analyses (CCA). The CCA ordination determined salinity to be the strongest influence of environmental gradients measured for both gastropod and bivalve distributions. Our results show that both molluscan diversity and median body size decrease as salinity concentrations move from marine to elevated salinity conditions. Predatory drilling frequency is not significantly influenced by salinity; however, there is a strong correspondence between predator and prey body size at marine to intermediate salinities, a relationship which dissipates at elevated salinities. This study reinforces the idea that small scale local environmental gradients can strongly influence biotic communities and that spatial and environmental variation must be considered in order to properly interpret temporal trends in the fossil record, even at sub-parasequence scales.