The interaction between Nereis diversicolor O.F. Müller and Corophium volutator Pallas as a structuring force in a shallow brackish sediment

Abstract

Distributional patterns of the polychaete, Nereis diversicolor O.F. Müller and the amphipod, Corophium volutator Pallas, were studied in an estuarine, shallow soft-bottom on the south coast of Sweden. For 2 yr our study site was divided into a “ Corophium patch” with high densities of Corophium and low densities of Nereis and a “ Nereis patch” with high densities of Nereis and low densities of Corophium. In the third year Corophium almost disappeared from our study site. This great reduction of Corophium densities was a general phenomenon in the coastal region around our study site. In the absence of Corophium, Nereis reached the same densities in the “ Corophium patch” as in the “ Nereis patch”. Laboratory experiments support our conclusion that high densities of Nereis reduce the density of Corophium — mainly through the effect of disturbance and not predation. A survey of the literature indicates, that Corophium may have a negative impact on recruiting Nereis. We suggest, that biotic interactions are the main factor preserving the observed patchiness at our study site, while accidents of history break up patchiness patterns.