Fish diversity in European lakes: geographical factors dominate over anthropogenic pressures

Aim To analyze the importance of regional and local factors on broad-scale patterns of fish diversity in European lakes and to assess the overall influence of anthropogenic pressures, with a focus on eutrophication. Location 1632 lakes from 11 European countries Methods We compiled data from standardized fish monitoring with multi-mesh benthic gill nets and on lake morphology, geographical, climatic and anthropogenic pressure variables. By means of regression tree analysis we assessed the relationship between fish assemblage descriptors (density, richness, diversity, evenness and biomass:number ratio) and environmental and pressure variables, and identified the thresholds best discriminating the resulting fish assemblage structure. Results. Fish density (biomass and numbers) was positively related to the total phosphorus concentration in the lakes and a concentration around 20 to 24 μg L-1 represented a threshold for a significant increase in lake fish densities. Fish density was also sensitive to geographical/climatic factors. Thus, warmer and lower-altitude European lakes, usually more eutrophied, tended to have higher fish densities and lower biomass:number ratios than cold and higher-altitude European lakes. Fish species richness and diversity were mainly related to morphologic and (bio)geographical/climatic variables, respectively, and larger and deeper lakes in warm areas of Europe tended to be the richest and most diverse in species. Main conclusions Our results suggest that the diversity of fish assemblages and fish body size were mainly determined by geographical/climatic gradients, whereas lake morphological factors were more important for determining species richness. Lake productivity overrode the effect of regional factors on fish density, but no relationship could be observed between fish assemblage structure and other anthropogenic stressors. These findings have implications for the development of fish-based assessment methods for lakes as nutrient state, morphology and geographical/climatic variables have to be considered when assessing the effects of anthropogenic pressures on fish richness and diversity.

JRC.D.2 - Water and Marine Resources