Selecting macroinvertebrate taxa and metrics to assess eutrophication in different depth zones of Mediterranean lakes

In this paper we investigate the response of macroinvertebrates and several metrics based on their presence/absence to eutrophication in some Mediterranean lakes of the volcanic district of Italy. A large dataset was assembled from previous studies comprising presence/absence of macroinvertebrate data from 185 sites located in three different depth zones (sandy eulittoral, vegetated infralittoral and sublittoral /profundal zone) of five lakes sampled between 1976 to 2004. Lakes were assigned to trophic categories based on total phosphorus and Secchi depth annual means. For each depth zone, species composition and richness-based metrics were compared between the different lake trophic categories. Results showed that species composition differed among lake zones and, in each depth zone, among sites belonging to lakes of different trophic state. Using a cut off value of 60 %, 23 taxa in the eulittoral, 31 in the infralittoral and 14 in the sublittoral/profundal were selected by the SIMPER routine as indicators of different trophic categories. The metric based on molluscan and large crustacean taxa was significantly higher in oligotrophic sites compared to eutrophic ones in all the three benthic zones, whereas the BMWP and ASPT scores and total taxa richness correctly differentiated between sites of different lake trophic category only in the sublittoral/profundal zone. We conclude that eutrophication pressures could be assessed by the use of certain richness-based metrics not only in the sublittoral/profundal but also in the sandy eulittoral and vegetated infralittoral zones.