Prevalence, patterns, and effects of shell damage on Geukensia demissa in South Carolina estuarine habitats |
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Authors: | Rachel Hillard Keith Walters |
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Institution: | (1) Department of Marine Science, Coastal Carolina University, P.O. Box 261954, Conway, SC 29588, USA |
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Abstract: | Shelled molluscs frequently exhibit a record of damage on exterior surfaces that can evidence past predation attempts and
may affect survival and growth. In South Carolina populations of the ribbed marsh mussel, Geukensia demissa, >90% of the individuals and up to 60% of the total shell area are damaged. A trend toward greater amounts of damage occurred
on mid-marsh compared to oyster reef mussels from the barrier beach side of inlets. Shell damage effects on survivorship and
shell and tissue growth were assessed seasonally during multi- and single-season field experiments. Mussels from a common
mid-marsh site were divided into size classes (~50 or 70 mm), treated to create two damage levels (undamaged and damaged),
and replaced within mid-marsh exclusion cages to minimize additional shell damage. In both multi- and single-season experiments
increased shell damage resulted in significantly greater mortality. Linear shell growth was unaffected by increased damage,
but 50 mm mussels grew twice as fast. Shell mass increased 16–50% in the multi-season and single-season winter period, but
decreased 7–12% during the single-season summer period. Tissue mass significantly decreased 31–43% in 50 mm damaged mussels,
but increased by 33% for 70 mm mussels in both multi-season and the single-season winter period experiments. Shell damage
did reduce tissue mass 43% in 70 mm single-season summer mussels. Experimental results indicate shell damage from a simulated
increase in predation can affect negatively both survival and growth of marsh mussels. Seasonal timing of shell damage and
initial mussel size also influenced the effects of sublethal predation on shell and tissue growth. The previously unrecognized
importance of sublethal predation and the resultant significant negative effects of shell damage on survival and growth will
affect the distribution and population dynamics of G. demissa in coastal marshes and will influence the overall contribution of ribbed mussels to estuarine ecosystems. |
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