374-377 Baden.p65

Seagrasses are aquatic flowering plants that occur worldwide and may be abundant on soft and sandy bottoms along coastal margins (1). In recent decades, a decrease in aerial extension has occurred mainly along industrialized coasts. This is documented throughout many distributional areas (2) and is one reason why seagrasses are listed in the Rio-declaration (1992/93:13) as habitats worthy of protection. The declaration further directs ratifying states to map marine ecosystems of high biodiversity and production. In this context, seagrass meadows (Chap. 17, part D 17.86 d) are especially emphasized. Seagrass meadows have important ecological and economic roles. As a biotope, seagrass generally exhibits high production and biodiversity of associated fauna (3–7), considerably higher than vegetation-free bottoms at the same depth (7). In an attempt to estimate the ecological and economic value of various ecosystems, Costanza et al. (8) found that coastal ecosystems contribute to more than 30% of the goods and services provided by the ecosystems of the world. Of these coastal services half are from seagrass and algae beds affecting nutrient fluxes by storage, internal cycling, processing, and acquisition. With all limitations involved in these types of calculations the values for seagrass and algal beds were estimated at USD 19 000 ha yr, about 10 times the estimated value of tropical rain forests. water (13), though eelgrass can withstand salinities ranging from 5.5 to 35‰ and brief periods of temperature exposure to 40°C or encasement in ice (1). Distribution in Scandinavia varies from the fully saline environment in Skagerrak into the brackish Baltic Sea at 61°N with a salinity of 5.5‰ (9). Resident fauna associated with eelgrass on the Swedish Skagerrak coast, many of which exhibit habitat-specific relationships, include the pipefishes, Syngnathus typhle and Nerophis ophidion, black goby, Gobius niger, grass shrimp, Palaemon adspersus, and fifteen-spined stickelback, Spinachia spinachia (4). Eelgrass meadows are also important nursery grounds for juveniles of commercial fish like cod, Gadus morhua, and whiting, Merlangus merlangus (14). In the Baltic Sea, the dominant associated species include the isopod, Idotea baltica, and fishes like perch, Perca fluviatilis, flounder, Pleuronectes flesus and roach, Rutilus rutilus (15). Eels, Anguilla anguilla, are common throughout the eelgrass meadows from the Skagerrak to the Baltic. Inventories of the shallow coastal areas were assessed along the Swedish west coast for coastal zone management purposes. Detailed mapping of sediment habitat types, including presence of phanerogams, were important components for decisions on dredging operations, locations of boat harbors and aquaculture ventures. The aim of the present investigation was to revisit about 2000 ha of Zostera marina inventoried during the 1980s along the Swedish Skagerrak coast using analogous techniques while also increasing mapping accuracy by using a Global Positioning System (GPS) for outlining the seagrass meadows in the field.