Hitchhiking bryozoans (Gymnolaemata) on sea turtles (Cheloniidae) from southeastern United States to Honduras

Abstract

To understand the symbiosis between epizoic bryozoans and sea turtles, we examined 52 sea turtles whose range spanned from Georgia, United States to Honduras, from three host species: Caretta caretta (loggerhead), Chelonia mydas (green), and Eretmochelys imbricata (hawksbill). Of these, 13% were adults and 87% were juveniles. We found 18 bryozoan colonies belonging to seven different gymnolaemate bryozoan species. Five were cheilostomes (Biflustra arborescens, Biflustra cf. conjunctiva, Bugula neritina, Schizoporella errata, and Aetea sp.) and two were ctenostomes (Alcyonidium hauffi and Anguinella palmata). Biflustra cf. conjunctiva and Aetea sp. are reported here for the first time on sea turtles. Biflustra cf. conjunctiva is an invasive species from the South China Sea and reported here for the first time in the southeastern United States. Of the 52 sea turtles examined, 15% were fouled by bryozoans: 88% of the loggerheads, 3% of the greens, and none of the hawksbills. Combining all host species, 86% of adult sea turtles were fouled by bryozoans compared to 4% of juveniles. Fouled hosts were significantly larger than unfouled hosts. We attribute this to the target area hypothesis, as the juvenile sea turtles were significantly smaller targets for bryozoan larval settlement than the adult hosts. The bryozoans were all found on the hosts’ dorsal carapace, and the number of bryozoan colonies increased significantly in a posterior direction across the carapace. Of the 18 bryozoan colonies, 89% were encrusting and 11% were erect, yet flexible. We describe this non-obligate/facultative commensal symbiotic relationship as phoretic (i.e., hitchhiking).