Trophic state assessment based on zooplankton communities in Mediterranean lakes

Eutrophication assessment is made widely using Carlson Trophic State indices (TSI) [e.g. secchi disc depth (TSISD)] or phytoplankton biomass. Recently, two Carlson type indices using rotifers (TSIROT) and crustaceans (TSICR) were developed from Polish lakes. In the present study, both indices were applied to zooplankton communities from 16 Greek lakes, covering the entire trophic state spectrum, in order to test their application in a different climatic zone, the Mediterranean. The evaluation of the indices (TSIROT and TSICR) was made comparing the trophic state of each sampling/lake based on TSISD and mean summer phytoplankton biomass. Both indices increased across the eutrophication gradient but misclassify the trophic state. We propose a new index, TSIZOO, the average of the formulae TSIROT and TSICR which are significantly correlated with the eutrophication proxies. All three zooplanktonic indices can efficiently detect low (oligotrophic-mesotrophic) and high (eutrophic-hypertrophic) trophic state using the boundaries < 45 for TSIROT and TSIZOO and < 50 for TSICR. All zooplanktonic indices are promising and effective tools for monitoring and assessment of eutrophication of Mediterranean lakes when mean values are used. Still, TSIZOO should be preferred as the best index that correlated with eutrophication which had the best estimations.