Wadden Sea: Study shows noticeable changes

Oldenburg. According to a new study, biological diversity in the Wadden Sea has changed dramatically over decades. Populations of many fish, plants, and birds are declining, as a research team from the Universities of Oldenburg and Groningen reports in the journal "Global Change Biology." The scientists systematically and holistically investigated how the number of organisms per species and location in the Wadden Sea has changed over time.

For this purpose, the team reportedly collected data from 200 stations along the Wadden Sea coast between Den Helder in the Netherlands and Blåvand in Denmark. The oldest information dates back to 1900, with more data available since the 1970s and 1980s. "Our method could therefore help identify the local threat to individual species at an early stage," says Oldenburg marine ecologist Anika Happe.

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The researchers found that the Wadden Sea ecosystem has noticeably reorganized over time. Only a few populations have remained unchanged. For example, the populations of Atlantic cod and flatfish have declined, and a downward trend has also been observed for many mussels, snails, seagrass, and salt marshes. Among the winners are newcomers to the mudflats, such as the Pacific oyster and the American razor clam.

According to the study, the population sizes of fish that use the Wadden Sea as a nursery, of plants that stabilize the coastline, and, since the early 2000s, of birds that use the Wadden Sea as a resting place along their migration route or as a breeding ground have declined in particular. According to the study, although most seabird populations initially increased, the numbers of many waders and gulls have been declining since the late 1990s and early 2000s.

Negative developments frequently occurred in related species. The researchers assume that these species have similar survival strategies and could therefore suffer together from changing environmental conditions. The team now plans to investigate the causes of these changes in further studies.

RND/dpa