Patterns of Distribution of Two Barnacle Species on the Mangrove Crab, Scylla serrata

Two lepadomorph barnacle species, Octolasmis angulata and O. cor, were commonly found living together in the branchial chambers of the mangrove crab, Scylla serrata. Patterns of distribution are a reflection of cyprid choice at crab ecdysis. Among the 6648 barnacles observed, there were roughly twice as many O. cor as O. angulata (3670 to 1758). The remaining barnacles were indistinguishable as to species and included 1014 immatures, 168 cyprids, and 38 peduncles. The spatial distributions of both O. angulata and O. cor on the gills of Scylla serrata are nonrandom, uneven, and do not reflect available surface area. Both species are distributed differently on the hypobranchial (inside) and epibranchial (outside) surfaces of the gills. Both species are distributed differently on the gills of immature (<70 mm carapace width) and mature (>70 mm) crabs. Our data also show that the distribution patterns vary with different densities. Support is presented for the hypothesis that current flow through the gill chamber may be an important factor influencing site selection by cyprids.