Changes in the seagrass populations of the Dutch Waddenzee

Abstract

A survey is given of the changes in the seagrass populations in the Dutch Waddenzee. A comparison of maps of the distribution in 1860 and 1930 shows that considerable changes took place before the “wasting disease” destroyed the sublittoral Zostera marina populations in the Waddenzee. These changes have to be regarded as normal long-term fluctuations within the large-scale pattern of the dynamic equilibrium of the Waddenzee ecosystem. In 1932 the “wasting disease” reached The Netherlands. The eulittoral populations of Z. marina did not succumb to it, while the eulittoral Z. noltii was not affected at all. In the period between 1932 and 1965 some quantitative fluctuations were noticed in the eulittoral populations of Z. marina and Z. noltii. After 1965 a general decline of both Zostera species commenced and is still in progress. This decline is no doubt a consequence of the increasing pollution, but the responsible factor has still not been ascertained beyond doubt.