Disentangling the relative roles of natural and anthropogenic-induced stressors in shaping benthic ciliate diversity in a heavily disturbed bay

Coastal areas are facing biodiversity loss and degradation of habitats due to intensified human activities. However, our understanding of the relative contribution of natural gradients and human induced disturbance to biodiversity is limited. Here, we investigated the response of three facets of alpha and beta diversity of benthic ciliates to environmental gradients in a highly disturbed estuarine bay in China. We used linear regression and distance-based redundancy analysis to determine the key driving factors for biodiversity. Variation partitioning was further used to examine the relative influence of natural gradients and anthropogenic disturbances on ciliate communities. Our results revealed that ciliate alpha diversity and functional composition remained similar despite notable variation in species composition along salinity gradient. Sediment grain size, together with heavy metals were the strongest determinants in shaping both alpha and beta diversity. After controlling for the effect of natural factors, heavy metals still had significant impacts on beta diversity. Human induced nitrogen enrichment was positively correlated with algivorous functional group with possible impacts on benthic food webs. These results suggest that beta diversity is overall more sensitive to anthropogenic stressors than alpha diversity and give important insights into the role of anthropogenic disturbance on coastal diversity, being also useful for developing ecosystem protection and conservation strategies.