Date of Award

6-30-2016

Document Type

Open Access Dissertation

Department

Marine Science

First Advisor

James L. Pinckney

Abstract

Saltmarshes are among the most productive ecosystems globally. At North Inlet estuary, South Carolina, about one third of the primary production comes from benthic microalgae. During the tidal cycle, mobile microalgae vertically migrate through the upper 3 mm of sediment. At low tide, algae are vulnerable to a variety of grazers, including the mud snail, Ilyanassa obsoleta, which is abundant in tidal creeks. Many species of intertidal snails have been shown to significantly alter the community structure and density of microalgae within the sediment. The purpose of this study was to determine how I. obsoleta affects the benthic microalgae community in an intertidal mudflat. This study found that I. obsoleta moved at an average speed of 3.3 ± 1.4 cm min-1 and that it could cause a significant decrease in the concentration of total chlorophyll a when grazing an area with low snail density, but not in areas with high snail density. Areas where snails congregated were characterized by significantly higher moisture than low density snail areas. In the laboratory, snails were introduced to petri dishes with both grazed and ungrazed sediments. I. obsoleta spent more time on sediment that had been previously grazed by its conspecifics. When snail cues were introduced to both sides of the dish, snails showed no clear preference for location, indicating that I. obsoleta likely uses chemical cues to locate conspecifics and congregate towards them, despite the competition for food. Chemical cues and desiccation risk are therefore the likely driving factors for I. obsoleta distribution on the mudflat, rather than the availability of their benthic microalgae food source.

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