Predation of Mussels - Maddy Gillis

Sublethal predation is common and extensive in intertidal estuarine environments. In the ribbed marsh mussel, Geukensia demissa, failed decapod predation can remove external shell layers, reducing growth rates and increasing non-predatory mortality. It is typically beneficial for mussels to repair their shells, however, shell repair is not an automatic response. Atlantic blue crabs, Callinectes sapidus, prefer to prey upon smaller mussels, but in handling time experiments crabs opened a few larger mussels at faster rates than expected. This suggests that crabs are able to detect and exploit vulnerabilities in mussel shells. My research is broken up into two experiments. The first is to determine when mussel shell repair occurs and if the shell repair rate is dependent upon the severity of shell damage. To do this I will divide 300 mussels into three size classes with three damage treatments (no damage, light damage, and heavy damage) and place them in the mid-marsh in mesh cages. Damage will be made by sanding the shell until the ridges are no longer distinguishable. I will sample twenty mussels from each treatment each month from April through August and measure the mussels' dimensions, mass, and shell thickness. The second experiment is to determine if crabs can detect weakened mussels, and if crabs preferentially predate upon mussels with damaged shells. To do this, I will place blue crabs into choice tanks with two possible scenarios. The first is with undamaged mussels on one side and damaged mussels on the other, and the second is with artificially damaged mussels and mussels with exterior scars but possible internal repair. After the crabs eat a mussel I will determine if shell repair is present by measuring the shells for thickness and mass. The results of these experiments will hopefully fill the current gap in the literature on mussel-blue crab interactions by accounting for the various affects of shell damage.