Life in the dead shell: utilization of dead Pinna shells by the blenny fish Petroscirtes variabilis Cantor, 1849 (Blennidae)

The seagrass ecosystem supports a diverse range of marine life, including fish, crabs, and seahorses. It plays a vital role in providing essential services such as habitat creation, nutrient cycling, and shoreline stabilization. In the present study, we conducted line intercept transects to assess the abundance of Pinna shells in seagrass meadows of the Sangumal region in the Palk Bay, India. Among the 30 transects surveyed, we observed a total of 33 Pinna shells. Ten shells were found to be empty, while 6 hosted blenny fish. The fish were identified as saber-tooth blenny Petroscirtes variabilis Cantor, 1849, via integrative taxonomy (morphology + cytochrome oxidase subunit I gene phylogeny). The phylogenetic tree based on the maximum likelihood inference method indicated that P. variabilis clustered together with other sequences of P. variabilis available in the NCBI GenBank. We also revealed the importance of empty Pinna shells acting as refugia for blenny fish, which was evident from the presence of eggs attached to the shells.