Can morphometrics and shell preference behaviour be a tool for hermit crab species identification?

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The hermit crabs are 'ecosystem engineers' and are a critical link in the oceanic food web. Six species of genus Coenobita are reported in the group of Andaman and Nicobar Islands namely, Coenobita rugosus, C. brevimanus, C. violascens, C. perlatus, C. cavipes and Birgus latro. In the present study, Coenobita rugosus, C. brevimanus, and C. violascens were chosen and handpicked randomly during low tides at two locations along the Port Blair Coast. During the study, important morphometric parameters viz, shield length (SL), carapace length (CL), cheliped propodus length (ChPL), cheliped dactylus length (ChDL), left third pereopod propodus(L3PL) and left third pereopod dactylus length(L3DL) were measured using a vernier calliper. Among the six parameters, shield length (SL), Cheliped Propodus length (ChPL) and cheliped dactylus length (ChDL) are important for species differentiation. Identification of hermit crabs belonging to the same or different genera becomes easier with the use of morphometric data along with the taxonomic keys in the absence of colour patterns. One-way ANOVA showed that there are significant differences in SL values among the three species. It was found that the mean values of SL varied significantly between males and females for C. rugosus (one-way ANOVA) and C. violascens, but there was no significant variation of SL values between males and females of C. brevimanus. The results showed that C. rugosus occupied variety of gastropod shells belonging to families Turbinidae, Muricidae, Trochidae, Strombidae, Buccinidae, Neritidae, Cerithidae, Cymatidae, Olividae and, plastic debris like discarded bottle caps. Whereas C. violascens preferred shells of Turbinidae and Muricidae but the C. brevimanus chose only the shells of Turbinidae at least during the present study period. The sex ratio was highest (1.58) in C. rugosus followed by C. violascens (1.14) and the lowest (0.39) in C. brevimanus. The individuals of C. brevimanus were significantly larger while C. rugosus were smaller based on the cheliped and carapace length and the body weight.