Coexistence of Juvenile with Adult Ocypode gaudichaudii at Culebra Beach, Panama: A Temporal-spatial Partitioning Compromise.

The temporal-spatial resource use patterns of juvenile and adult Ocypode gaudichaudii were studied by comparing the zonation patterns and activity budgets of the two life stages at Culebra Beach, Panama. Burrow distribution of the crabs during the day and at night was studied over six months. Diurnal activity budgets of 46 crabs (22 juveniles and 24 adults) were determined by observing seven predominant behaviors upon emergence from their respective burrows when the burrow zone is uncovered after the tide recedes. The behaviors comprise three foraging-related activities (i.e., deposit-feeding, scavenging, and probing for food), the maintenance of burrow, walking, staying within the burrow, and resting at the burrow entrance. Juvenile crabs occupied a higher intertidal zone than the adults and had a higher emergence rate at night. This temporal-spatial habitat partitioning could possibly reduce intraspecific competition between the two life stages, thereby enabling their coexistence in the habitat as well as increasing the survival rate of the juveniles, potentially raising the carrying capacity of the population at Culebra Beach. All 46 crabs-regardless of life stage-spent the highest mean proportion of time on foraging-related activities. Out of the three feeding-related behaviors, adults spent most time on deposit-feeding while juveniles spent most time probing. Only juveniles scavenged. In both life stages, a similar proportion of time was spent maintaining the burrow and staying within the burrow.

Unique Behavioral Strategies Adopted by Gravid Ghost Crab Ocypode gaudichaudii to Overcome Dehydration Stress while Minimizing Predation Risks.

Semi-terrestrial crabs require continual access to water to maintain life-sustaining processes such as circulation and feeding. When they emerge from their burrows during low tide to forage, they face the problem of dehydration as they leave the dampness of their burrows. While foraging above ground, water uptake is elicited through capillary action via the hydrophilic setae near the base of the crab's body. Extruded eggs that are borne on the abdominal flap of females tend to obstruct the contact of the setae with the wet sediment. The behavioral adaptations that enable the gravid female painted ghost crab, Ocypode gaudichaudii, to overcome dehydration stress and minimize predation risks at a sandy shore in Playa Venao, Panama were studied using field observations. Comparison of the morphometric measurements of setal tufts between 30 male and 30 female crabs was made to determine if there were morphological adaptations. Analysis of the water uptake behavior from video footage showed that gravid crabs spent a longer duration on water uptake than crabs that did not carry eggs. For the first time, masquerading behavior of a gravid O. gaudichaudii was observed, in which the crab minimized predatory detection by freezing its movement next to a stone enroute to the lower shore during the day. There was no sexual dimorphism in the length and width of the setal tufts between the male and female adult crabs. The results of this study provide the first evidence that the water-uptake behavior in gravid O. gaudichaudii is dependent on behavioral adaptations, as setal tuft morphology does not differ between the sexes.

Plasticity of Foraging Strategies Adopted by the Painted Ghost Crab, Ocypode gaudichaudii, in Response to in situ Food Resource Manipulation Experiments.

The feeding strategies of Ocypode gaudichaudii at two sandy beaches, Culebra Beach (CB) and Playa Venao (PV) in Panama, were studied via three experiments. Two separate manipulative in situ experiments were conducted to determine how the densities of food resources and the size of the supplemented food offered to the crabs can affect their diet and food handling behavior. The third experiment, a transplantation study, was also conducted to determine the plasticity of the feeding behavior of the displaced crabs. In the first experiment, freshly-emerged crabs showed different feeding modes when washed-sediment was seeded with different densities of diatoms and rove beetles, which suggests that they are optimal foragers. Crabs hoarded food in the second experiment when food augmentation was performed, in which small and large food pellets were placed around the burrows at the beginning and end of the crabs' feeding cycle. All freshly-emerged crabs from both sites foraged on the small pellets outside their burrows and did not cache food; when pellets were provided at the end of the feeding cycle, crabs from CB fed on some of the small pellets and returned to their burrows with the uneaten pellets left on the surface, whereas crabs at PV picked up all the small food pellets and transferred them into their burrows over several trips before plugging their burrow entrances. Only the crabs from PV carried the large food pellets supplemented at the start and end of the feeding cycle into their burrows. In contrast, the crabs at CB often left behind the partially-eaten pellets on the sand surface, probably due to the increased risk of predation associated with the prolonged handling time of the large food pellets. Excavation of the burrows of the crabs that hoarded food showed that all the pellets were deposited at the bend of the burrows, indicating that they were not consumed immediately. Crabs that fed in droves at PV stopped droving and foraged around their burrows after being transplanted to CB. This is the first documentation of food hoarding in a sandy beach macroinvertebrate at a resource-impoverished habitat. The plasticity of feeding strategies adopted by the painted ghost crab in response to different densities of food resources in the habitat could be an adaptation to the dynamic sandy beach environment.