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

Area of Science:

• Marine Biology
• Crustacean Taxonomy
• Ecology

Background:

• Hermit crabs are vital ecosystem engineers and a critical link in oceanic food webs.
• Six Coenobita species inhabit the Andaman and Nicobar Islands, including Birgus latro.
• Understanding their morphometrics and ecological roles is crucial for marine conservation.

Purpose of the Study:

• To differentiate three hermit crab species (Coenobita rugosus, C. brevimanus, C. violascens) using morphometric parameters.
• To investigate variations in morphometric data, including shield length (SL), between sexes.
• To analyze shell occupancy patterns and sex ratios of these hermit crab species.

Main Methods:

• Random handpicking of hermit crabs during low tides at Port Blair Coast.
• Measurement of key morphometric parameters: shield length (SL), carapace length (CL), cheliped propodus length (ChPL), cheliped dactylus length (ChDL), left third pereopod propodus (L3PL), and left third pereopod dactylus (L3DL) using vernier calipers.
• Statistical analysis including one-way ANOVA to determine significant differences in morphometric parameters and sex ratios.

Main Results:

• Shield length (SL), Cheliped Propodus length (ChPL), and Cheliped Dactylus length (ChDL) were identified as key parameters for species differentiation.
• Significant differences in SL were found among the three species.
• Sex-specific variations in SL were significant for C. rugosus and C. violascens, but not for C. brevimanus.
• C. rugosus occupied a wide variety of gastropod shells and plastic debris, C. violascens preferred Turbinidae and Muricidae shells, while C. brevimanus exclusively used Turbinidae shells.
• Sex ratios varied, with C. rugosus having the highest and C. brevimanus the lowest.

Conclusions:

• Morphometric data, particularly SL, ChPL, and ChDL, are effective for differentiating hermit crab species, especially when color patterns are absent.
• Significant sexual dimorphism in shield length exists in C. rugosus and C. violascens.
• Hermit crab species exhibit distinct preferences in gastropod shell selection and use of anthropogenic debris.
• Species size varied, with C. brevimanus being significantly larger and C. rugosus smaller.