Stonefly Response to Salinity
Aquatic insect larvae and other aquatic organisms are exposed to multiple stressors in high altitude glacial-melt streams and low temperature waters - including low nutrients, low salinity (total dissolved solids), potential exposure to ice, and hydraulic conditions that become torrential during the summer melt season. One of our research questions is, "how will aquatic nymphs adjust to greater salinity as the glaciers melt and streams become more similar to groundwater streams with salinity above background glacial-melt levels?"
Aquatic ecotoxicologists have examined the tolerance of aquatic nymphs to increased salinity in temperate streams where salinity is moderate-to-high due to the impacts of mining and road salt applications. In order to better understand the ability of nymphs in extremely low salinity of glacial meltwaters to adjust to greater salinity as the glaciers dissapear and groundwaters become prominent, we conducted several field experiments in the circum-Himalayas to expose stonefly nymphs to a range of salinities. We found that Chloroperlidae stoneflies living further downstream from the glacier potentially have a better ability to survive and adjust to increased salinities than Nemouridae stoneflies inhabiting the metakryal zone (Tmax< 2oC) closest to the glaciers. Additional studies examining stonefly nymphs and their osmoregulation capabilities would strengthen our knowledge of how stoneflies and other insects might fare under climate-change scenarios.
We also utilized exposure of nymphs to silver nitrate to examine for the presence of chloride cells and scanning electron microscopy (SEM) imagery to examine the morphology of chloride cells after exposure to salinity treatments. The nymphs that survived longer in the high salinity treatments showed changes to chloride cell morphology. Further molecular studies could help us to better understand any potential phenotypic plasticity that chloride cells exhibit under changing environmental conditions.
Because of their specialized habitats, glacial-meltwater nymphs are potentially some of the most endangered aquatic insects because their habitats are shrinking up the mountains with the receding glaciers under climate warming conditions.