66.5 Saturday, Jan. 5 Nomadic Ghosts: Patterns of Burrow Occupancy in the Ghost Crab Ocypode quadrata ERNST, D.A.*; BROTHERS, J.R.; LOHMANN, K.J.; University of North Carolina at Chapel Hill email@example.com
The ghost crab, Ocypode quadrata, is a semi-terrestrial crab indigenous to sandy, western Atlantic beaches. During summer months, crabs dig burrows into the beach and take refuge underground during daylight hours, emerging at night to forage over considerable areas. Relatively little is known, however, about burrow use and occupancy. As a first step toward determining whether crabs return to the same burrow each morning or instead find or excavate new ones, crabs on a beach in eastern Florida were captured after sunset using traps that fit over the burrow entrance. Each crab was marked and then released either outside the burrow entrance or within the burrow. The following day, traps were set at the same burrows. Among the 30 burrows where crabs had been released outside, 63.3% were occupied the next day; of the occupants, 94.7% were new arrivals rather than crabs that had occupied the same burrows the night before. Among the 30 burrows where crabs were released inside, 76.7% were occupied the next day; in this case, however, about half of the occupants (47.8%) were previous residents, whereas the other half (52.2%) were new arrivals. These data imply that many crabs take up residence in burrows that they did not excavate themselves. To further investigate whether ghost crabs opportunistically occupy empty burrows, artificial burrows (n=30) were constructed at a number of locations along the beach. Trapping results revealed that 33.3% of these new burrows were occupied within 24 hours. Taken together, the results suggest that many ghost crabs fail to return to the same burrow after a night of foraging and that crabs often occupy unfamiliar burrows opportunistically. Hypotheses regarding the observed burrow occupancy patterns will be discussed.