The effects of limpet morphology on predation by adult cancrid crabs

Limpets are important prey for some crab species, yet little is known about the role of the limpet shell in defense against crab predation. In an effort to identify limpet shell morphologies that decrease vulnerability to predation by adult cancrid crabs, laboratory feeding trials using three common species of Pacific Northwest limpets (Lottia digitalis, L. pelta and L. scutum) were conducted to assess how different shell morphologies affect mortality and handling time. Large size, shell ornament (radial ridges), and low-spired geometry were expected to result in increased survivorship, and/or longer handling times. Although mortality varied between species, no relationship between size and increased survivorship was observed. Contrary to the expectation that radial ribs resist predation, individuals with smooth morphologies experienced lower mortality. Furthermore, binomial logistic regression indicated that the presence of shell ornament was the only significant explanatory variable in predicting mortality. As species possessing high-spires and ridges may typically occur high in the intertidal where predation risk due to crabs is relatively lower, shell ornament is likely an adaptation to physical factors such as thermal stress, and does not appear to be antipredatory for limpets.