Exploring the effects of salinization on trophic diversity in freshwater ecosystems: a quantitative review

Salinization of freshwater ecosystems represents a potential threat to biodiversity, but the distribution of salinity tolerance among freshwater organisms and its functional consequences are understudied. In this study, we reviewed global patterns of salinity tolerance across a broad range of freshwater organisms. Specifically, we compared published data on LC50 (a metric of salinity tolerance) across climatic regions, taxa, and functional feeding groups (FFGs). We found that microinvertebrates were more sensitive to salinity than vertebrates and macroinvertebrates. Within aquatic insects, there was considerable variability in tolerance across FFGs. Specifically, scrapers, gatherers, and filterers were more sensitive on average than omnivores, shredders, and predators. Thus, we predict that increasing salinization can negatively impact trophic diversity and in turn cause overall changes in the structure and function of freshwater ecosystems. We also identified both historical exposure and taxonomic affinity as potential drivers of contemporary salinity tolerance across freshwater organisms. Finally, we found important gaps in our understanding of the potential impacts of salinization on freshwater biodiversity, particularly in regions expected to be affected by increased salinization due to climate change and secondary salinization. Understanding the differential vulnerability of freshwater taxa is critical to predicting the ecosystem impacts of salinization, and informing conservation and management decisions.