Brooks, W. Randy

Previous studies indicate that hermit crabs may use the blood or hemolymph from dying crabs to locate the soon-to-be-vacated shells. In this study, I determined and characterized the responses of hermit crabs to hemolymph from various crustaceans. Hermit crabs tested included members of the Diogenidae: Dardanus venosus, Clibanarius tricolor, C. antillensis, C. vittatus, and Calcinus tibicen; and Paguridae: Pagurus longicarpus and P. annulipes. Test odor sources included the previously mentioned hermit crabs plus seven additional odors, including three non-anomuran crustaceans. Most significant responses to hemolymph were to species within the same family. In several cases, the strongest responses were to conspecifics or congenerics. These results show clearly that hermit crabs in general use chemicals from other hermit crabs as cues for finding new shells. These results also show that the shell a crab occupies influences its response to odors, illustrating the role of context in these interactions.

Some species of hermit crabs can locate chemically predation sites where snails are consumed and subsequently obtain their shells. This study addressed four questions: (1) Is chemotaxis to snail odors prevalent among hermit crabs? (2) Do members of hermit crab lineages respond similarly to common snail odors? (3) Do hermit crabs respond more acutely to snails whose shells they most frequently occupy? and (4) Does phylogeny of snails influence responses by hermit crabs? Two sets of congeners (Clibanarius vittatuslC. tricolor and Dardanus venosuslD. fucosus) in the family Diogenidae, and three congeners (Pagurus pollicaris, P. longicarpus, and P. annulipes) in the family Paguridae were tested. Fifteen species of snails from 11 families served as test odors. Hermit crab response was measured by the fondling display, where one hermit crab investigates the shell of a neighboring crab. The diogenids discriminated odors more readily than did the pagurids. Correlations between responses and shells most frequently occupied existed for C. vittatus and D. venosus. Clibanarius tricolor was the only crab to respond to confamilial test odors.

Host specificity by Periclimenes pedersoni and P. yucatanicus to three species of sea anemone was investigated. Field associations, initial preferences (within 72 h of collection) in the laboratory, and changes in preference after "conditioning" with an alternate host were compared. Periclimenes pedersoni associated with Bartholomea annulata in the field preferred this same anemone in choice trials. These same shrimp changed preference after 2 to 8 wks of conditioning with a different host species. Periclimenes yucatanicus associated with Stichodactyla helianthus in the field preferred this same anemone in choice trials. Those P. yucatanicus collected from either Condylactis gigantea or B. annulata did not exhibit an initial preference for these respective hosts. Periclimenes yucatanicus initially found on and preferring S. helianthus did not change their preference after conditioning; those found on other hosts chose S. helianthus after conditioning.

Periclimenes yucatanicus, P. pedersoni, and Thor sp. were nonrandomly distributed among three anemone species at different sites off southern Florida. Host selection tests showed that P. yucatanicus had a strong preference for one anemone, which could explain its field abundance with this same species. Host location tests showed that both Periclimenes species used chemical cues to detect their anemones--visual information seemed unimportant. Laboratory predation trials showed that shrimp survived significantly longer with an anemone than without in the presence of predatory fishes. The acclimation behavior of Periclimenes was described to analyze the protection mechanism. Legs and antennae were in frequent contact with the anemone, but the other body regions rarely contacted the tentacles. Additionally, antennae were used frequently to direct tentacles away from these other body regions. Coating of high contact areas with anemone mucus and avoidance of tentacles with other areas may be the method of protection.

The Sargassum community is comprised of a unique and diverse assemblage of organisms. Habitat detection by two of the most common invertebrates, Latreutes fucorum and Leander tenuicornis , was investigated. Results of this study do not support that either L. fucorum or L. tenuicornis respond to chemical cues released by the Sargassum habitat in the absence of other information. Habitat selection of both shrimp species was examined as well. Both L. fucorum and L. tenuicornis selected live Sargassum over artificial Sargassum . Moreover, L. fucorum selected Sargassum natans over Sargassum fluitans when only visual cues were available, whereas large-sized L. tenuicornis selected S. fluitans under the same conditions. Conversely, habitat selection trials combining both chemical and visual cues resulted in no preference between the two Sargassum species by either shrimp species. Additional ecological factors that possibly influence habitat location and selection are discussed as well as the importance of Sargassum in terms of pelagic fisheries management.

Predator-prey relationships were studied between the shrimps Latreutes fucorum and Leander tenuicornis and the predatory fishes Stephanolepis hispidus and Histrio histrio, all found within pelagic Sargassum communities. Average survival times of shrimps were compared in species, size/density, and habitat selection studies. The results showed that S. hispidus had a preference for prey species while H. histrio did not. 30 mm shrimp survived longer than the 10 mm shrimp for both S. hispidus and H. histrio. Density was a factor in the survival times of the 20 mm shrimps with S. hispidus only. L. tenuicornis survived longer in artificial Sargassum habitats with H. histrio. The larger shrimps survived longer in the artificial habitats than the smaller shrimps with S. hispidus. Both fish predators employ optimal foraging strategies with similarities and differences, the latter of which are likely related to behavioral differences in the these predator and prey.

Coral bleaching involves the loss of symbiotic algae (zooxanthellae) from reef corals and other cnidarians during periods of environmental stress, particularly elevated temperature. In this study the thermal bleaching responses of the zoanthid Palythoa caribaeorum from three populations along the southeast coast of Florida were compared. Winter (2002--2003) and summer (2003) samples from three geographically separate sites were exposed to increased temperatures and the loss of zooxanthellae was measured. Zooxanthellae populations were sampled and identified using PCR-DGGE. The results showed that samples of P. caribaeorum from reefs that experience smaller annual thermal ranges released the most zooxanthellae. Seasonal comparisons revealed winter samples experienced a greater amount of zooxanthellae loss than summer samples. P. caribaeorum was found to harbor two genetic strains of zooxanthellae, C1 and D1a. Colonies either contained monotypic populations of these, or a combination of both.

Host selection by Dissodactylus crinitichelis and Clypeasterophilus rugatus for different echinoderms was investigated. Initial preference (within 24 h of collection) and preference after "conditioning" with an alternate host were compared. D. crinitichelis initially preferred its field host, the sand dollar Encope michelini, but after conditioning switched its host preference to a non-field host, the sea biscuit Clypeaster rosaceus. This switch in host preference after conditioning occurred despite consumption of numerous crabs (86 out of 167) by C. rosaceus. Clypeasterophilus rugatus initially preferred its field host, the sea biscuit Clypeaster rosaceus, but showed little change in host preference after conditioning. These results indicate significant behavioral differences in these closely related crabs in their association with echinoderms. Chemical detection by the crabs was investigated, and no significant use of chemical cues by adults or juveniles of either species was found, even though chemical responses have been observed in other closely related pinnotherid crabs. Using the checkered pufferfish, Sphoeroides testudineus, as a predator, the possibility that crabs may receive protection by living with echinoderms was also examined. Crabs with echinoderms survived significantly longer than crabs without echinoderms, which is the first direct evidence that these crabs are protected by associating with echinoderms.