INFERRING DIET OF CRABS USING WEAR PATTERNS ON CLAWS

Durophagous crabs have claws that appear to be well adapted for crushing shells, although their claws may also be used for burrowing, defense, and display. A proxy for diet separate from claw morphology is, therefore, necessary to independently test the influence of durophagy on claw evolution. Although diets of living crabs can be inferred by direct observation of wild feeding habits, experimental feeding trials, and gut content analyses, no proxies of diet other than claw morphology have been developed for fossil crabs. We here test whether wear patterns of crab claw teeth can serve as a proxy for the degree of durophagy in crab taxa.

The movable fingers of claws from life and death assemblages of the mud crab Panopeus were collected from 13 separate intertidal oyster reefs along the U.S. Atlantic and Gulf coast. The molts of laboratory-raised crabs lacking hard-shelled diets were used as controls. Shape of the occlusive margin of crab fingers was quantified and described using outline-based elliptic Fourier descriptors, and textures of these margins also were examined with a SEM. These data were compared to gut contents of 111 preserved crabs from two Florida Panopeus populations. C, N, and S stable isotope data also were collected from the organic component of fingers from both life and death assemblages of Florida Panopeus.

Comparisons of morphometric data with SEM images confirm that tooth shape reflects degree of wear. Results also show that the population of crabs with the greatest percentage of shells in their stomachs also had the highest degree of wear on their teeth. Further, Atlantic life assemblages exhibited significantly less tooth wear than their associated death assemblages, suggesting a recent shift in diet. Wear patterns and C and N isotope values between Gulf life and death assemblages were not significantly different. These results indicate that wear patterns on crab teeth may serve as reliable proxies for diet in both living and fossil crab taxa.