The presence of the bivalve Cerastoderma edule affects migration, survival and reproduction of the amphipod Corophium volutator

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Abstract
An amensalistic interaction between the common cockle Cerastoderma edule (L.) and the amphipod (Corophium) volutator (Pallas) is reported. C. edule may attain very high densities in soft-bottom localities. In an intertidal flat in the Danish Wadden Sea densities (1 yr cockles) of about 3500 ind m-2 were observed. The area fraction occupied by the cockles gives a better indication of their potential impact on coexisting species. Thus, a population in the outer part of the intertidal flat was found to cover 30 to 40% of the area. Previous observations had indicated that high densities of cockles negatively affect C. volutator. Laboratory and field enclosure experiments demonstrate an amensalistic effect by the suspension-feeder C. edule on the deposit-feeder C. volutator. In C. volutator migration rate increases, and survival, growth and reproduction decrease with increasing density of C. edule. It is suggested that these effects are caused by the burrowing and ploughing habits of cockles, which inhabit the same upper 3 to 4 cm of sediment as C. volutator. Consequences for the distribution of C. volutator are discussed. In field experiments, recruitment of the deposit feeding bivalve Macoma balthica (L.) was also found to be negatively dependent on area occupied by cockles.