Eelgrass in the Waddenzee and Zeeland delta
The sharp decline in eelgrass beds has resulted in an extraordinary ecosystem being all but lost.
Trends in the Zeeland delta
In the 1970s and 1980s there were over 4000 ha eelgrass (common eelgrass and dwarf eelgrass) in the Grevelingen and Oosterschelde. Little now remains. Over 20 years the area of the Zeeland delta under the dwarf eelgrass shrank by 90%, while the area under common eelgrass shrank by 98%.
The most important cause of the decline is the cessation of inputs of freshwater via the Hollands Diep and small rivers in Brabant, The Delta Works prevent this water from reaching the Grevelingen and the Oosterschelde, so the water is now too saline for eelgrass.
Trends in the Waddenzee
In 1869 the area of eelgrass in the Waddenzee was 6000 ha. In 1930 there were still beds of eelgrass in large parts of the western Waddenzee (see figure), but shortly afterwards these beds disappeared. A few can be found today near Terschelling in the estuary of the Eems near Delfzijl.
Eelgrass declined sharply throughout the North Atlantic in the 1930s. This was generally attributed to the ravages of a single-celled parasite. Though the eelgrass recovered somewhat, in 1970-1990 there was another sharp decline, this time because the Waddenzee had become too turbid. The transparency improved after 1980, but eelgrass has not yet returned to the western Waddenzee, possibly because of a lack of seeds or other propagules. There has been some recovery in the eastern Waddenzee and the Eems.
On 7 June 2002, as part of a reintroduction programme lasting from 2001 to 2005, young plants of eelgrass were planted between Den Helder and Wieringen
Common eelgrass and dwarf eelgrass are both on the Red List of vascular plants.
Implications for other species
Eelgrass beds form a distinctive biotope in which numerous species found a suitable habitat. The virtual disappearance of the eelgrass beds has also led to the disappearance of the associated fauna, such as two shellfish (thick-lipped spire shell and banded chink-shell) and two fish species (sea stickleback and deep-snouted pipefish).
