Post-settlement mortality of juvenile lagoonal cockles (Cerastoderma glaucum : Mollusca: Bivalvia)

Abstract

Like many benthic marine invertebrates the lagoonal cockle Cerastoderma glaucum Bruguière (Mollusca: Bivalvia) suffers extensive mortality between settling out of the plankton and reaching adolescence. It is thought that predation could be a major cause of this mortality. Experiments were conducted in aquaria to assess the influence of predation on the survival of juvenile lagoonal cockles. Newly settled spat (collected from Holkham Salts Hole, a lagoon in North Norfolk) were enclosed with potential predators at field densities. Predators used were fish, prawns and polychaetes (singly or combination). The numbers and sizes of the surviving cockles were measured after a 4-week period to establish the extent of predation, and the results were consistent with predation by the fish (Pomatoschistus microps) being a major causative agent of the mortality seen in the field. This reinforces the idea of epibenthic predation as an important structuring element for marine benthic communities. The effect of post-settlement juvenile mortality on cockle population demographics is considered, and other possible causes of mortality in the field are discussed.