30/01/2006 - This report contributes to the development of tools that can be applied to assess the five classes of ecological status of the Water Framework Directive based on the biological quality elements phytoplankton, macroalgae and macrobenthos. The work on phytoplankton biomass (Chl a) based on moni-toring data and historical Secchi depth measurements provides a first step in establishing reference conditions for phytoplankton in Danish waters. The identification of appropriate macroalgal indicators provides the results that total cover and cumulated cover of coastal macroalgal communities are suit-able indicators of water quality.

The results also indicate that a strategy with focus on algae from deeper, light-limited waters and exclusion of algae from shallow exposed waters renderes algal indicators sensitive to changes in water quality. The macrobenthos project evaluates some of the earlier pro-posed indices on Danish data along the environmental gradient of oxygen deficiency.

Results from this evaluation indicate that both diversity-based indices and the sensitivity based index AMBI can be used to evaluate quality status of benthic communities in Danish waters. The result applies to bot-toms in the salinity regime > 18 psu.