Investigating the effects of increased salinity on leaf litter decomposition and mortality of an aquatic invertebrate detritivore (Caecidotea sp.)

Context: Coastal freshwater wetlands and their associated communities are at an increased risk of salinity exposure because of a variety of contemporary and historical anthropogenic stressors. Salinization shifts the community structure of aquatic organisms, such as macroinvertebrates, leading to decreases in functional ecological integrity. These salinity-driven changes to communities have the potential to alter macroinvertebrate-mediated processes such as detrital decomposition. Aims: Our study aimed to examine the relationship among salinity exposure, leaf decomposition and mortality of a common freshwater macroinvertebrate (isopod: genus Caecidotea). Methods: Using an in-laboratory microcosm approach, we exposed tanks of isopods and detrital leaf material to varying salinity levels for 23 days, after which isopod mortality and decomposition of detrital material were measured. Key results: We found that increases in salinity increased isopod mortality, but had no effect on leaf disc decomposition. Conclusions: These findings demonstrated the negative effect of increased salinity on a common freshwater macroinvertebrate. Additional studies regarding the response of non-isopod decomposers, such as bacteria and fungi, are needed to provide a more complete understanding of the effects of salinity intrusion in at-risk freshwater habitats. Implications: As we expect salinization to increase in the future, it is important to understand how organisms and the processes they contribute to and rely on will be affected. The detrital decomposition process and aquatic macroinvertebrates are key foundations of aquatic food webs, and significant bottom-up changes could have drastic implications for ecosystems.