Diversity, size frequency distribution and trophic structure of the macromollusc fauna of Vavvaru Island (Faadhippolhu Atoll, northern Maldives)

Little is known about the malacofauna of the Maldives despite the ecological significance and diversity of molluscs in tropical coral reef ecosystems.We qualitatively collected molluscs with shell sizes of approx-imately 1 cm or larger at different major habitats (lagoon, reef flat and reef drop-off) at Vavvaru Island, northern Maldives. Shells collected on the beach supplemented the species inventory. Two hundred fifty-eight species were found, including 180 gastropods from 45 families, 75 bivalves from 23 families, and 3 ceph-alopods from 3 families. Seventeen families were represented by five or more species, with Muricidae (20 spp.), Conidae (20 spp.) and Cypraeidae (17 spp.) being most speciose. Maximum shell size ranged from 7 to 450 mm, with a median of 34 mm. Fifty percent of the species had shell sizes ranging between 21 and 50 mm; only 4.8 % exceeded 100 mm. The median shell size of gastropods was 34 mm, that of bivalves 32 mm. The most common trophic category was predatory carnivores (38.8 % of mollusc species), followed by suspension feeders (22.5 %). Among gastropods, predatory carnivores accounted for more than half (53.9 %) of the species. Suspension feeders were the most common (72.0 %) trophic category among bivalves. Our survey provides the first faunistic data on molluscs from Vavvaru as well as new records for the Maldives. We probably captured the diversity of large and common shallow-dwelling species at the lagoon and reef flat well, and increased sampling effort would most likely have predominantly added rare and small species to the inventory. In contrast, at the much less intensively sampled drop-off, further large and common species can also be expected. The low number of mollusc species from the largest size classes and the preponderance of carnivorous species among gastropods are typical features of coral reef mollusc communities and have also been reported from other tropical settings such as the Caribbean, East Africa, the Red Sea and New Caledonia.