Importance of predation by crustaceans upon bivalve spat in the intertidalzone of the Dutch Wadden Sea as revealed by immunological assays of gut contents

Predation on bivalve spat (Macoma balthica, Cerastoderma edule and Mya aren aria) by crustaceans was studied in an intertidal area in the western Dutch Wadden Sea in 1993. In all species settlement started at the end of April. Peak numbers were reached in the beginning of June of about 4300 ind. m(-2 ) in Macoma, 1300 in Cerastoderma and 500 in Mya. During June and July numb ers dropped sharply to low levels at a mean size of 1.0 to 1.5 mm. Instanta neous mortality rates over this period varied from 0.045 d(-1) in Fnrncorna to 0.056 d(-1) in both Cerastoderma and Mya. Immunoassays of gut contents of brown shrimps Crangon crangon and shore crabs Carcinus maenas positively identified both species as predators on bivalve spat. The high shrimp dens ities observed (100 ind. m(-2)) in combination with their simultaneous pres ence with the post-larval bivalves indicate that juvenile shrimps are likel y the most important predator. The estimated predation pressure by crustace ans, and especially the brown shrimp, is sufficient to account for the obse rved mortality rates among bivalves. Bivalve recruitment, however, did not appear to be regulated by crustacean predation: during the period of predat ion, bivalve mortality was not density-dependent. Information on bivalve pr edation in Swedish bays support this view. (C) 1998 Published by Elsevier S cience B.V. All rights reserved.