Stable mussel Mytilus edulis beds in the Wadden Sea - They're just for the birds

Abstract

Predation by eiders, oystercatchers and herring gulls on natural mussel beds Mytilus edulis was studied in the Königshafen, a sheltered bay in the Wadden Sea. About 15 ha (2.5%) of the Königshafen were covered with mussel patches of a biomass of about 1300 g AFDW m-2. The biomass on the mussel beds was dominated by old mussels and found to be constant over several years. Birds annually removed 30% of the standing stock. Eiders were by far the most important predators and consumed 346 g AFDW m-2, followed by oystercatchers with 28 g AFDW m-2 and herring gulls with 3.6 g AFDW m-2. Birds consumed a substantial part of the annual production of the mussel beds which was estimated from literature data to be approx. 500 to 600 g AFDW m-2. As other predators were absent, the production of the mussels was sufficient to sustain the high predation rate by birds. Stable mussel beds form a short and efficient link between primary production and bird predation which is unusual for the Wadden Sea, where the main part of primary food supply is thought to be unavailable for higher trophic levels.