Regional Studies in Marine Science 40 (2020) 101507 Contents lists available at ScienceDirect Regional Studies in Marine Science journal homepage: www.elsevier.com/locate/rsma Variability in benthic invertebrate community structure near warm water effluents of a power plant in the southern Caspian Sea Morteza Farshchi, Ali Nasrolahi ∗ , Mohammad Reza Shokri Department of Animal Sciences and Marine Biology, Faculty of Life Sciences and Biotechnology, Shahid Beheshti University, 198 396 9411, Tehran, Iran article info Article history: Received 1 April 2020 Received in revised form 7 October 2020 Accepted 10 October 2020 Available online 12 October 2020 Keywords: Warming Power plant effluent Macrobenthic communities Caspian Sea abstract 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. © 2020 Elsevier B.V. All rights reserved. 1. Introduction During the last century, human activities have severely in- creased, which consequently led to an increase in the production of greenhouse gases, especially CO 2 . This, in turn, has caused the temperature to reach its peak in the past 1400 years (IPCC, 2014). The Earth’s surface has been warmed by 0.8 ◦ C since the industrial revolution, which resulted in ocean warming (IPCC, 2014; Stocker et al., 2013) with the potential to change the physicochemical characteristics as well as biological conditions of the seawater (Seibel, 2011). It, therefore, can impact ecosystems and the communities therein (N.R.C (National Research Council), 1981). In a smaller scale, thermal pollution may have similar impacts in some areas of the sea (Arieli et al., 2011). Thermal pollution is a reduction in water quality that stems from changes in water temperature. This type of pollution in tropical areas, where ambient water temperature is naturally high, elevates the water temperature, sometimes to the point that it may exceed the thermal threshold of some organisms and cause adverse effects on them (Langford, 2001; Poornima et al., 2005; Kimmerer and Weaver, 2013; Cardoso-Mohedano et al., 2015). The common type of thermal pollution is mainly caused by power ∗ Corresponding author. E-mail address: A_Nasrolahi@sbu.ac.ir (A. Nasrolahi). plants, which use seawater for cooling the system. The output warm water is then released into the sea, which may change the ambient temperature regime and other abiotic parameters (e.g., oxygen) and, therefore, change the physiology of animals (Langford, 2001; Galil and Zenetos, 2002; Murray, 2006; Bianchi, 2007). Warm water effluent can alter the structure, composition and performance of fish, phytoplankton, macrophyte and benthic communities (Langford, 2001). The influence of thermal pollu- tion driven from the output water of coastal power plants have been previously studied on many marine organisms including phytoplanktons and periphytons (Rajadurai et al., 2005; Poornima et al., 2005; Chuang et al., 2009; Jiang et al., 2013; Lo et al., 2016), red algae (Wolf et al., 2014), fish (Teixeira et al., 2009, 2012), foraminifera (Arieli et al., 2011; Titelboim et al., 2016) and macrobenthic communities (Lardicci et al., 1999; Bensoussan et al., 2010; Riera et al., 2011; Mazik et al., 2013; Bozorgchenani et al., 2018). The massive attention towards studying the effects of thermal effluent demonstrates its applicability to be used as a model for predicting the effects of global warming on the marine biota of coastal ecosystems (Worthington et al., 2015). Benthic communities are among the most important groups of marine organisms with a significant role in the food web (Gogina et al., 2010; Baldanzi et al., 2013; Nicastro and Bishop, 2013) and regulating physical, chemical, geological, and biological processes (Sivadas et al., 2010; Birchenough et al., 2011). These organisms have limited movement, long life span and live on https://doi.org/10.1016/j.rsma.2020.101507 2352-4855/© 2020 Elsevier B.V. All rights reserved.