Variability in benthic invertebrate community structure near warm water effluents of a power plant in the southern Caspian Sea

Anthropogenic changes to the temperature regime of a water body, including but not limited to climate change and thermal pollution, may influence the community structure of species living therein. Among these, benthic communities, due to their limited movement and long life span, are one of the best biological indicators to reflect the impact of environmental stressors. In this regard, the thermal pollution of Pare-Sar power plant in the southern Caspian Sea was used as a natural laboratory to assess the effects of warming on macrobenthic communities’ biomass, abundance, richness, and structure throughout the year. Water temperature near the effluents of the power plant was on average 1.29 °C higher than the control sites. We observed that warming led to an increase in the abundance and species richness of benthic macroinvertebrates. However, benthos biomass was significantly lower in the impact site rather than the control sites, probably due to the increased proportion of small-bodied taxa and decreased growth rate of biomass determinant taxa. Therefore, our findings may be an indication of potential benthic community response to thermal pollution and may provide a baseline for future projections under global climate change scenarios.