Changes in benthic diversity and ecosystem function I response to organic enrichment from fish farming.

The benthic enrichment gradient was studied in four Mediterranean areas affected by fish farms. In every area the macrofauna species composition, abundance and biomass was determined at 6 sampling stations and a series of diversity metrics were calculated. For better understanding of the environmental change, in addition to the biotic
indices, a number of geochemical variables (redox potential, labile and refractory organic matter, MD, sulfide concentration, Phosphorus concentration etc) and ecosystem processes (oxygen consumption, mineralization of nitrogen) were measured for every gradient. The nonparametric rank correlation analysis between all possible
pairs of diversity, geochemical and ecosystem function variables in the data set showed a large number of significant positive or negative correlations. Furthermore, in order to study the combined effect of changes in sediment geochemistry and biodiversity metrics we used multiple stepwise regression using ecosystem function
descriptors (O2 consumption, N mineralization) as dependent variables. This analysis resulted in multiple regression models explaining a large proportion (60-90%) of the variability of the data. Our results indicate that ecosystem function changes considerably in response to both geochemical variables and biodiversity metrics.