Predation of the endobenthic invertebrates Nereis diversicolor and Arenicola marina on Macoma balthica spat

The tellinid bivalve Macoma baithica (L.) (Mollusca, Bivalvia) is a common and widespread macrobenthic species on the tidal flats of the Wadden Sea. In May, the barely settled juvenile M. baithica migrate to higher places on the tidal flats, so called nurseries. The juveniles leave these nurseries again when they grown up to 2-8 mm, at the onset of winter and return to the lower parts of the tidal flats where they stay the rest of their live. It is assumed that the choice of juvenile M. baithica to use nurseries is mainly determined by the difference in predation pressure at different tidal levels. Juveniles avoid the predation of aquatic epibenthos such as shrimp, crabs and flat fish on the lower tidal flats by migrating to nurseries. Adult M. baithica avoid the predation of birds by returning to the lower parts of the tidal flats. This study showed that carnivorous endobenthic polychaetes N. diversicolor and A. marina also feed on M. baithica spat. Juvenile M. baithica has been recovered from both predators that were caught in the field after analyses of digestive tract contents. Also predation experiments in the laboratory have pointed out N. diversicolor and A. marina as endobenthic predators of juvenile M. baithica. A significant reduction of bivalves has been demonstrated in the predation experiments with both N. diversicolor and A. marina and also some of the consumed M. baithica have been retrieved in the predators after dissection. Estimation of the mortality of M. baithica caused by these predators shows both N. diversicolor and A. marina to be of large impact on M. baithica population size.