Population characteristics of abundant bivalves (Mollusca, Vesicomyidae) at a sulphide-rich seafloor site near Lihir Island, Papua New Guinea

Abstract

Extensive beds of sulphide-habitat-associated clams are present on the summit of Edison Seamount (1450 m depth) near Lihir Island, Papua New Guinea. These vesicomyids represent a new species. Imagery indicates that two major fields are several hundred metres in size. Four large grabs yielded over 270 live clams up to 23 cm in length plus many shells. The size structure of the populations suggests that settlement occurs in cohorts and that successful recruitment occurs mostly in areas with few adult clams. Dead juveniles were most abundant in the grabs with dense adults. Images from a towed camera sled included scales to allow density estimates that range up to 240 clams/m2(in small patches) with sizes averaging around 16.5 cm in length. A biometric relationship for length to wet mass allows calculation of estimates of biomass represented by clams measured in photographs. The average biomass value in Lihir clam beds is 13.3 kg/m2, with maximum values over 29 kg/m2(wet mass including shells). We compare these values with those of other studies that retrieved fewer specimens or imagery. We suggest that several overestimates populate the literature but that values around 30 kg/m2rival the biomass of intertidal bivalve beds.