Declining salinity and increasing temperature reduce the diversity and resilience of benthic diatoms

Climate change will modify the marine ecosystem in several ways, but the effects of changing climate on benthic diatoms, which are one of the most important photosynthesizing organism groups in benthic habitats, are poorly studied. We conducted a mesocosm experiment to investigate the effects of increasing temperature and decreasing salinity on the taxonomic and functional diversity of benthic diatoms. We showed that decreasing salinity affects the taxonomic and functional composition of communities, and the threshold salinity for community composition is ~5. This indicates that when climate change leads to decreasing salinity in brackish systems, the most pronounced changes in communities occur in areas where salinity decreases from >5 to <5. We also showed that both increasing temperature and decreasing salinity exert stress on communities and, hence, lead to the decrease of the alpha and beta diversity of communities. This indicates that climate change reduces the size of the species pool of diatoms. Our results show that, along with the changing climate, we can expect benthic diatom communities to become less diverse and less resilient.