EXPERIMENTAL TAPHONOMY OF THE BLUE CRAB, CALLINECTES SAPIDUS: ENVIRONMENTAL AND CUTICULAR CONTROLS ON PRESERVATION

Hypotheses about cuticle preservation in decapod crustaceans abound, but most are based upon little supporting data. Calcification of the cuticle, especially in the fingers and claws, is commonly identified as the primary determining factor for cuticle preservation. This investigation examines the causes for differential preservation of crab cuticle. Callinectes sapidus Rathbun, the blue crab, was selected for study due to its abundance and wide geographical range. Extrinsic factors were studied by placing specimens in fine-mesh (0.5 cm) bags and deployed in the Gulf of Mexico and the Bahamas. These sites included carbonate and terrigenous settings, various depositional environments, and depths ranging from 50 m to 600 m. Bags from each site were collected after five- and nine-year time intervals. A semi-quantitative score sheet was produced, rating each specimen on what sections of cuticle remained and the degree to which it had degraded. Results show disarticulation of finger tips and teeth from the rest of the claw, possibly due to rapid chemical and structural shifts in the cuticle. Finger tips and teeth preserve well and often exhibit little damage. Some sections of the remainder of the claw preserve well, but very little carapace remains in deployed samples. Preliminary analysis shows disarticulation and dissolution rates are not dependent on depth or substrate. Only in extreme cases does salinity play a role; extremely high levels result in “pickling” of crabs, leading to long-term preservation of both soft and hard parts. Rate of burial and length of deployment greatly affect cuticle preservation. Intrinsic factors of preservation were studied using freshly-caught blue crabs. EDAX dot mapping reveals increasing levels of calcite concentration and crystallization along the length of the claws and in the finger tips and teeth. Thin section examination and high resolution CAT scanning documented changes in degree and density of calcification. These geochemical gradients demonstrate that calcite density and distribution within cuticle correlates directly with preservation potential as observed in the experimentally deployed samples. The differential preservation potential of crab cuticle has strong implications for the fossil record of the Decapoda.