AN ECOLOGICAL CASCADE EFFECT - MIGRATORY BIRDS AFFECT STABILITY OF INTERTIDAL SEDIMENTS

A comprehensive study of factors controlling the erodibility of fine-g rained intertidal sediments found that sediment strength increased wit h the arrival of large numbers of migratory shorebirds. Before the bir ds came, sediment cohesion resulted in part from secretion of polysacc harides by benthic diatoms whose production was controlled mainly by a grazing amphipod, Corophium volutator. When the birds arrived, Coroph ium behavior and abundance changed, bioturbation and grazing pressure on the diatoms decreased, and production of cohesion-inducing carbohyd rates rose. The results emphasize the importance of biological process es in affecting sediment stability and the limitations of laboratory-b ased measurements of sediment properties used in models of cohesive se diment behavior.