Infestation by Octolasmis species (Lepadiformes, Poecilasmatidae) of the marine crab Lupocycloporus gracilimanus (Decapoda, Portunidae) from India

Abstract

Abstract The portunid crab Lupocycloporus gracilimanus from Digha, Bay of Bengal, India was investigated for an infestation by the lepadomorph cirriped Octolasmis spp. About 93% of the epibionts examined were found attached to the surface of the carapace, abdomen and legs, and these were identified as Octolasmis warwicki (EOW). Only 7% of the epibionts were attached to the branchial lamellae, and these were identified as Octolasmis angulata (EOA). Twenty-seven O. warwicki were also found to have conspecific dwarf males (CDM) attached to the scutum: probably an adaptive strategy to maximize the total insemination. Both the epibionts and the CDM showed spatial preference for the posterior mesobranchial region of the carapace. Most of the CDM (27%) were seen as a single attachment on the epibiont. The distance between the epibiont and its nearest neighbour (DNN) was found to be strongly and negatively correlated (, ) with the number of epibionts, indicating its preference to stay in an intermediate-sized group rather than remain solitary, which probably would have facilitated the evolution of dwarf males (CDMs). A higher percentage of epibionts were observed to have attached CDMs when the DNN increased, and above the 25 mm DNN, all epibionts were having CDM attachments, which is believed to be a strategy to maximize the fertilization success of CDMs by reducing sperm competition. A strong, positive correlation (, ) was observed between the carapace width of the host crab and the numbers of the infesting epibionts, proving that the larger crabs are more susceptible to the infestation compared to the smaller ones. The sex ratio of the host crab was 1 : 5.5 (Male : Female), nevertheless, only the females were infested by the epibionts. The percentage of the prevalence, relative abundance and mean intensity of EOW infestation were recorded as 46.15%, 182.05% and 394.44%, respectively. None of the crabs had serious external or internal infestations that seemed to hinder the activities of the animal. This is the first report of the infestation of these Octolasmis species on the portunid crab Lupocycloporus gracilimanus from India.