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

ABSTRACT: 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.

SUBMITTER: Yong AYP

PROVIDER: S-EPMC8662320 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:Atlantic ghost crabs (Ocypode quadrata) are predators of beach-nesting shorebird nests and chicks on the United States' Atlantic and Gulf coasts. Ghost crabs may also disturb birds, altering foraging, habitat use, or nest and brood attendance patterns. Shorebird conservation strategies often involve predator and disturbance management to improve reproductive success, but efforts rarely target ghost crabs. Despite the threat to shorebird reproductive success, ghost crabs are a poorly understood part of the beach ecosystem and additional knowledge about ghost crab habitat selection is needed to inform shorebird conservation. We monitored ghost crab activity, defined as burrow abundance, throughout the shorebird breeding season on Metompkin Island, Virginia, an important breeding site for piping plovers (Charadrius melodus) and American oystercatchers (Haematopus palliatus). We counted burrows at shorebird nests and random locations throughout the breeding season and investigated whether ghost crab activity was greater at nest sites relative to random locations without shorebird nests. While we observed burrows at all nest sites (n = 63 nests), we found that burrow counts were lower at piping plover nests with shell cover, relative to random locations with no shell cover. Ghost crabs may avoid piping plover nest sites due to anti-predator behaviors from incubating adults or differences in microhabitat characteristics selected by piping plovers. We also investigated the effects of habitat type, date, and air temperature on the abundance of ghost crab burrows. We found that while crab burrows were present across the barrier island landscape, there were more burrows in sandy, undisturbed habitats behind the dunes, relative to wave-disturbed beach. Additionally, ghost crab activity increased later in the shorebird breeding season. Understanding when and where ghost crabs are most likely to be active in the landscape can aid decision-making to benefit imperiled shorebird populations.

Dataset Information

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

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