Report: Macroalgae — Seagrass (Zostera): Evaluation system WFD — Weser — Elbe (2006)»

“This report presents an assessment system under the EU Water Framework Directive for the quality component macrophytes (angiosperms and macroalgae) in coastal and transitional waters. This assessment system has been developed exemplarily for the coastal and transitional waters of the Weser and the coastal waters of the Elbe. Nevertheless, it is also entitled to be applicable to the transition waters of Elbe and the water bodies of the same type in the adjacent river basin districts (Ems, Eider). The evaluation system is based on the evaluation of historical and recent sources for the distribution and development of seagrass and macroalgae stocks in the German North Sea Coast since the beginning of the 19th century. On the basis of these sources, a list of the species potentially found in the area was first compiled and a description of the various biotope types characterised by macrophytes was made. The species range includes 2 seagrass species and 152 macroalgae species, including 61 green, 65 brown and 56 red algae. The occurrence of these species is largely limited to stable substrates in the euphotic zone of water bodies. Accordingly, they react sensitively to a deterioration of the light climate (increase in water opacity) and to the influence of hydrodynamic forces (sea passage, current) or other mechanical stresses (e.g. fishing). The macrophytes show reduced water quality, on the one hand, by the decline in seagrass populations and perennial red and brown algae species, on the other hand by the massive increase in green algae development. Based on this experience, the evaluation system was built. For the development of the system and the definition of class boundaries for the individual quality characteristics, existing or proposed assessment systems from different EU Member States have been evaluated. In this context, the index-based assessment methods “Location Type Index” (STI) and “ecological evaluation index” (EEI) are also discussed. Both methods are considered unsuitable for the processing area. The presented assessment system for macrophytes is based as a combined method on the classification of several quality characteristics of angiosperms and macroalgae. These are: Species of marine angiosperms; Expansion of seagrass stocks; Density of seagrass stocks (coverage); Number of red and brown algae species; Number of multi-annual species; maximum extent of summer green algae stocks (Eulitoral only); Biomass of opportunistic green algae and deep distribution of marine macroalgae. While a regular monitoring programme is already in place for the feature “extension of summer green algae stocks”, which also meets the requirements of the WFD, the monitoring investigations for the other components of the system still need to be redesigned or further developed from existing designs. Basic studies are necessary for the entire area of the euphotic sublitoral. It is encouraged to further develop the pre-framed evaluation system with the help of appropriately oriented research. In particular, it is proposed to draw up a potential distribution chart for seagrass in the Eu- and Sublitoral, based on the Dutch model.”