MEPS 241:113-123 (2002)  -  doi:10.3354/meps241113

Reduced epibenthic predation on intertidal bivalves after a severe winter in the European Wadden Sea

Matthias Strasser*

Alfred-Wegener-Institut für Polar- and Meeresforschung, Wattenmeerstation Sylt, Hafenstraße 43, 25992 List, Germany

ABSTRACT: One hypothesis to explain the phenomenon of high bivalve recruitment after severe winters in coastal North Sea sediments is reduced epibenthic predation. Using predator exclusion experiments, I tested the hypothesis that epibenthic predation on the juvenile bivalves Cerastoderma edule, Macoma balthica and Mya arenaria was lower after a severe winter (1995 to 1996) than after a moderate (1996 to 1997) and a mild (1997 to 1998) winter. In C. edule and M. arenaria there was 2 fold evidence for reduced epibenthic predation after the severe winter: (1) significant predation effects occurred only in exclusion experiments after the 2 milder winters but not after the severe winter; and (2) recruits attained larger sizes in August and October after the severe winter suggesting continuous growth rather than truncation of the size spectrum by predators. In M. balthica, predation effects were also significant only after the milder winters but there was no effect on size. In all 3 bivalve species, recruitment at the experimental sites in the fall was higher after the severe winter than after the 2 milder ones. These results suggest that high bivalve recruitment after severe winters is primarily caused by the post-settlement factor of reduced epibenthic predation on the tidal flats. The strategy to conduct several predator exclusion experiments in both sand and mud in 3 consecutive years with differential winter conditions, and while considering migration activity and size development in juvenile bivalves, proved useful to distinguish between cage artefacts and predation effects.

KEY WORDS: Winter effects · Recruitment · Intertidal · Predator-exclusion experiments · Cerastoderma edule · Macoma balthica · Mya arenaria

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