Does the Introduction of the Pacific Oyster Crassostrea gigas Lead to Species Shifts in the Wadden Sea?

Abstract

Over centuries dramatic changes have occurred in the species composition of the Wadden Sea, a shallow coastal sea bordering the North Sea. Natural dynamics as well as direct and indirect anthropogenic influences have resulted in the introduction and the disappearance of important benthic populations. Historic records and extensive surveys show large variability in benthic suspension-feeder stocks. Infaunal species like the cockle (Cerastoderma edule) are extremely variable over time and space, hence show a typical resilient response. Mussel (Mytilus edulis) beds seem to be more stable over time. Once lost, mussel beds need more time to re-establish bed structures. It is hypothesized that infaunal populations have a high resilience, while epifauna species are characterized by resistance to changes as they form structures like reefs or beds. On the basis of this hypothesis the consequences of new introductions can be evaluated. It can be expected that the recent introduction of the resistant reef-building epifaunal Pacific oyster Crassostrea gigas, will lead to shifts in benthic suspension-feeder populations and eventually will develop a new stable state for the Wadden Sea that potentially offers less food for birds. This situation may deviate considerably from the actual nature conservation objectives that focus on the role of the Wadden Sea as one of Europe's most important wetlands for migratory bird populations.