Molluscan assemblages under the influence of peat-draining rivers off East Sumatra, Indonesia

The central Indo-west Pacific biodiversity hotspot is of outstanding biological interest in terms of both taxonomy and ecology. However, the molluscan fauna of the region is poorly known. Here we present death assemblages of the subtidal (1–56 m) waters off Eastern Sumatra, Indonesia. Molluscan shells were sampled from a variety of settings from estuaries to coral reef-related carbonate environments. A total of 5064 shells was counted and 197 species were identified. Four shelly death assemblages which are defined by characteristic taxa are found in specific environments. A deposit-feeding community with low diversity and low abundances was recorded in settings with high amounts of terrigenous mud. Greater abundances and higher diversity were found farther offshore, especially in carbonate sediments in the vicinity of offshore islands where pteriomorphian bivalves are characteristic taxa. Protobranch bivalves, especially a species of Nuculana, appear to be best adapted to the organic-rich but food-limited, muddy substrate of the proximal marine environment influenced by peat-draining rivers. Thus, in addition to dominating deep-sea molluscan assemblages, some protobranch bivalves appear to be specialists in exploiting refractory organic materials of shelf environments.