Consequences of stressor-induced changes in species assemblage for biodiversity indicators.

Protection of biodiversity is a major objective in environmental management. However, standard protocols for ecological risk assessments use endpoints that are not directly related to biodiversity. In the present study, the changes in five biodiversity indicators, namely, the Hill, Shannon-Wiener, Simpson's diversity index, AZTI's Marine Benthic Index (AMBI), and Benthic Quality Index (BQI), are calculated in case species experience direct chemical effects. This is done for an uncontaminated situation as well as for situations in which the effect concentration of a certain fraction of species (x%) is exceeded, that is, at the hazardous concentration (HCx) of the species sensitivity distribution (SSD) of the considered community. Results indicate that the response of the biodiversity indicators to concentrations spanning the complete concentration range of the SSD is variable. This response depends mainly on the type of indicator, the species assemblage, and the ratio of the slope of the concentration effect curves of the species and the slope of the SSD. At the HC5, a commonly used threshold in environmental risk assessment, biodiversity indicators, are affected at a marginal level (change is less than 5% in 99.6% of the simulated cases). Based on the results, the HC5 level is likely to be a protective threshold for changes in biodiversity in terms of richness and heterogeneity in the vast majority of the simulated cases (99.6%) for chemicals for which direct effects are dominant.