Long-term population dynamics of breeding bird species in the German Wadden Sea area

Abstract

For no other group of organisms in coastal areas are there so exact and long-term data available as there are for seabirds. Since the beginning of the 20th century, documentation of population size, especially for species breeding in colonies from the groups gulls, terns and auks, is almost complete. These species act as bio-indicators, and data on fluctuations in their population size are useful as they reflect changes in the state of the marine ecosystem. The population development of some of these seabird species (Herring Gull, Guillemot, Common, Arctic and Sandwich Tern) from the German North Sea coast, which primarily feed on fish, is given. Common to all these species is an exponential increase in numbers in recent years (1970–1985). Possible causes for this development, e.g. pressure from enemies or competitors, availability of breeding places, anthropogenic stress and mortality factors, as well as the direct and indirect anthropogenic-influenced changes in the trophic system due to the increasing eutrophication of coastal waters, are evaluated. Signs of a collapse in the stocks of seabrids resulting from environmental pollution are discussed. Consequences resulting from the ecosystem changes, such as reduction of nutrient discharge into the North Sea and the expansion of biological monitoring, are described.