European Ocean Biodiversity Information System

Macroalgae It is possible to find macroalgae vegetation almost everywhere in Kattegat and the Belt Sea area and the western Baltic Sea where stone reefs are common. Salinity and light play an important role structuring the algae communities as do wave exposure at low water depth. In Denmark more than 300 species of red, brown and green algae species is registered. Macroalgae forest on stone reefs are considered as important habitats for a large number of fish and animals. Eelgrass Eelgrass is the most common marine angiosperm in Danish coastal waters where it dominates the vegetation on sandy substrates. Eelgrass plays an important part in coastal areas due to its large productivity and biomass. Eelgrass meadows are nursery areas for fish and invertebrates and the well-developed rhizomes contribute to stabilising the sediment and thereby reducing coastal erosion. Eelgrass grows from the coast and down to maximum depths that depend on water clarity. In the inner parts of estuaries, the deepest eelgrass patches typically occur at a depth of around 3 m, while along open coasts eelgrass typically occurs down to 5-6 m depth. The deepest registrations of eelgrass in Danish coastal waters are found at about 10 m. The cover of eelgrass typically describes a bell-shaped pattern with depth. Cover is low close to the coast where physical exposure generates loss of biomass, and in deeper water where light limits growth. Thus, maximum cover occurs at intermediate depths where exposure is moderate and light levels are still considerable. The monitoring programme in connection with the "Action plan for the marine environment" includes measurements of the depth distribution of eelgrass as well as of the percentage coverage of eelgrass. Reductions in nutrient loads are expected to reduce the biomass of phytoplankton, thereby improving water clarity and allowing eelgrass to grow at greater depths and obtain higher coverage in deeper waters. Data Data on species areal cover of macro-algae Information on sampling locations within the Danish national marine monitoring program (NOVA 2003) and download of data can be accessed through the MADS website.