Ecological indices: a biometric approach for assessing eutrophication levels in the marine environment

The efficiency of 12 ecological indices expressing species diversity, abundance, evenness, dominance and biomass of phytoplankton to describe trophic levels in coastal marine ecosystems in the Eastern Mediterranean was assessed. The phytoplankton data were derived from three reference data sets characterising different trophic levels: (a) from inshore Saronikos Gulf waters characterising eutrophication; (b) from offshore waters of Saronikos Gulf representing mesotrophic conditions; and (c) from the oligotrophic offshore waters of the Island of Rhodes, Aegean Sea. Some of the commonly used indices such as the Simpsonʹs, Shannonʹs and Margalefʹs indices seemed to be unsuitable for identifying eutrophic trends. On the other hand, the Menhinickʹs index, Kotheʹs index, Species Evenness, Species Number and Total Number of Individuals were found effective for distinguishing oligotrophic, mesotrophic and eutrophic waters, the most efficient being the Kotheʹs and Species Number indices. These indices were used to propose a classification scheme for characterising oligotrophic, mesotrophic and eutrophic waters in the Eastern Mediterranean. The experimental approach described in the present work can be used for water characterization in any waterbody, provided there are data available for setting up standard datasets that can define reference conditions.