The ecological status has to be assessed type-specific by means of characteristic water types, and has to be measured separately within certain geographical water units (water bodies). According to the WFD the ecological status has to be classified into five ecological quality classes:
For the assessment different physico-chemical, hydro-geomorphological and biological quality components have to be used. The biological quality components for coastal waters are phytoplankton, macrophytes (macroalgae and angiosperms) and macrozoobenthos. For rivers, lakes and transitional waters also fish is included. The classification schemes for these biological components should be based mainly on species composition, abundance and the presence/absence of sensitive species.
To ensure comparability of classification systems between member states, the results of the systems shall be expressed as ecological quality ratio (EQR). This ratio represents the relationship between the values of the biological parameters currently observed for a given water body and the values for these parameters for the reference conditions, i.e. without anthropogenic influence applicable to that body. The ratio is expressed as a numerical value between zero and one, with high ecological status represented by values close to one and bad ecological status by values close to zero.
MariLim was responsible or involved in the development of different assessment systems for the Baltic Sea:
- BALCOSIS (Baltic ALgae COmmunity analySIs System) – assessment system for macrophytes in outer Baltic coastal waters
- MarBIT (Marine Baltic Index Tool) – assessment system for macrozoobenthos
- PHYBIBCO (PHYtoBenthic Index for inner Baltic COastal waters) – assessment system for macrophytes in inner Baltic coastal waters
and is a regular member of the international intercalibration groups of the Baltic Sea (BalticGIG).