CAN TAPHONOMY AND ICHNOLOGY OF THE PAST BE USED TO MANAGE THE FUTURE? WHY THE DECLINE OF THE WEST INDIAN TOP-SHELL (CITTARIUM PICA) WILL AFFECT LAND HERMIT CRAB (COENOBITA CLYPEATUS) POPULATIONS

Conservation paleobiology, a field employing methods of paleontology to monitor and manage biodiversity, can provide invaluable insights to the consequences of exploitation and removal of species. Based on studies in Bermuda by Walker (1994) and Olson and Hearty (2013), there have been at least four extinctions and reintroductions of the West Indian top-shell (Cittarium pica) to Bermuda. Cittarium pica shells are extensively used by the terrestrial hermit crab, Coenobita clypeatus throughout the Quaternary. Fossil traces assignable to terrestrial hermit crabs are rare. The first walking crab trace was described from the Holocene of the Bahamas by Walker (2003). Currently there are conservation concerns regarding the overharvesting of Cittarium and the consequences for Coenobita populations. Coenobita is a significant scavenger and occupies a niche that would be filled by ant species if the crab populations collapse. To address this conservation concern, we collected data on shell use of Coenobita populations on San Salvador Island, Bahamas and used documentation of traces for estimating the number of breeding females of Coenobita. After fertilization, eggs are transported by female crabs for a month before being deposited into the surf. On San Salvador Island, females deposit eggs in a four day period associated with the July new moon. The timing of spring tides and wet sand increase the potential for preservation of trackways in the high tide berm. During this time, the female crab travels directly into the surf leaving a distinctive set of traces; as opposed to meandering along the high tide mark. Only the largest females, those predominately in Cittarium shells with heights > 60 mm, deposit eggs in the surf. This fact has profound consequences for conservation of the crabs, since overharvesting of large Cittarium shells for bait, food, or the marine curio trade would immediately have an impact on the breeding populations of hermit crabs. Our observations also provide insights regarding the reasons behind the sparse nature of terrestrial hermit crab traces in the fossil record. Females only enter the surf to deposit eggs a few days each year. Conversely, the use of crab traces is an extremely valuable tool for those using demographics to model crab populations for management purposes.