Date of Award

1-1-2011

Document Type

Campus Access Thesis

Department

Marine Science

First Advisor

Brian Helmuth

Abstract

Mechanistically determining an organism's physiological climate space, and its capacity to function within this space, is essential for predicting how populations will persist in novel environments. The goal of my thesis was to clarify how the salt marsh snail Littoraria irrorata experiences microclimate conditions within the canopy of Spartina alterniflora and to assess the role these conditions play in controlling its behaviors. I combined laboratory experiments with field observations to test the snails' physiological tolerances to thermal and desiccation stresses and to relate this to microclimate conditions in the high and low marsh of South Carolina. I also assembled a heat budget model to predict L. irrorata's ability to be active depending on its height in the S. alterniflora canopy and the timing of tidal emergence. In addition, I calculated total monthly activity times for May-September, 2005-2010. I found that the snails primarily responded to desiccation stress and therefore spent midday glued to stalks with mucus holdfasts at low heights in the canopy (~5cm in the high marsh), where desiccation stress was lowest. Much higher levels of thermal and desiccation stresses were observed in the high marsh than in the low marsh, particularly during a neap tide, when the high marsh site was emerged for several days. Marsh emergence periods began most frequently in the high marsh from 0:00-8:00, when calculated snail activity times were also highest. Furthermore, snail activity times were most constrained in July, and then increased into the Fall. The thermal and desiccation constraints on L. irrorata's ability to maintain activity corresponded with the behavioral patterns described in studies of its life history traits. The overall results of my thesis indicate that microclimate conditions in the salt marsh help to explain many characteristics of L. irrorata's behaviors and are likely to play a large role in its population dynamics.

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