Mussel monitoring

Mussel beds are among the most diverse communities in the Wadden Sea, serving as valuable food source and important habitat for birds and invertebrates.

Mussel monitoring serves to gain a yearly overview of the composition and structure of the mussel beds to document their long-term development.

Surveys of eulittoral mussel beds are mainly carried out between May and September. The mussel beds are visited from the shore or by boat to collect different data. In on-site inspections, the contours of the beds are determined by GPS and the coverage is estimated. Samples are taken and later evaluated in the laboratory to determine abundance, length frequency distribution, biomass and condition index of the mussels.

The species community of four typical beds is documented additionally. In September, the accompanying fauna is assessed to analyse structure and dynamics of endo- and epibenthos.

Twice every five years, complementary digital aerial surveys are carried out on behalf of the Nationalparkverwaltung (National Park Administration) to ensure comprehensive monitoring. These data are made available for further evaluation within the framework of mussel monitoring. Digital photographs of the entire North Frisian and partly Dithmarschen Wadden Sea are used to verify known beds as well as to identify freshly colonised eulittoral areas.

Sublittoral mussel populations are surveyed from the ship using a small mussel dredge, checking known sites as well as further areas. This method delivers valuable information about sublittoral sites that could partly be confirmed over several years.

The strategy to monitor mussels has been agreed between Denmark, Germany and The Netherlands in the Trilateral Monitoring and Assessment Program (TMAG 1991) Trilateral Monitoring and Assessment Program (see also Nehls & Büttger 2006).