Tolerance of glacial-melt stoneflies (Plecoptera) and morphological responses of chloride cells to stream salinity

Authors: FAIR, HEATHER - University Of Minnesota; LANNO, ROMAN - The Ohio State University; Smiley, Peter - Rocky

Submitted to: Chemosphere
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/14/2022
Publication Date: 1/17/2022
Citation: Fair, H., Lanno, R., Smiley, P.C. 2022. Tolerance of glacial-melt stoneflies (Plecoptera) and morphological responses of chloride cells to stream salinity. Chemosphere. 293. Article 133655. https://doi.org/10.1016/j.chemosphere.2022.133655.
DOI: https://doi.org/10.1016/j.chemosphere.2022.133655

Interpretive Summary: Decreases in aquatic insect survival in glacial-melt streams are predicted to occur with conductivity (dissolved inorganic ion concentrations) increases expected to occur in response to future increases in air temperature. We used salinity as a proxy for conductivity and conducted field bioassays in glacial-melt streams in China in 2015 and subjected immature aquatic stoneflies (green stoneflies, spring stoneflies, winter stoneflies) originating from streams with different conductivity levels to salinity levels representative of those expected in freshwater streams to elevated levels expected in brackish estuaries for nine days. Survival of green stoneflies did not differ among salinity treatments. Conversely, spring stoneflies and winter stoneflies exhibited reduced survival in the three greatest salinity treatments. The salinity concentration predicted to kill 50% of the stoneflies did not differ among stoneflies from stream sites with different conductivity levels. The number, density, and area of one type of chloride cells (caviform cells) decreased with increasing salinity only within green stoneflies that exhibited the greatest salinity tolerance. These findings are novel because they represent the first documentation of the survival, median lethal concentrations, and sublethal morphological responses of stoneflies from China to elevated conductivity levels. Our novel results will also be of much interest to those involved with watershed management and conservation of aquatic biodiversity in Tibet and China because they provide information that can be used to understand how anthropogenic increases in conductivity can affect aquatic invertebrates within glacier streams in Asia. Our results combined with information from other headwater stream studies will also be of interest to state agencies, federal agencies, private consulting companies, and non-profits involved with the management of agricultural headwater streams in the United States because they indicate that stoneflies, which is an aquatic insect that is commonly used as a water quality indicator, can tolerate short term increases in conductivity.

Technical Abstract: Aquatic insects within glacier-melt streams are adapted to low dissolved inorganic ion concentrations (salinity). Increases in dissolved inorganic ion concentrations in glacial-melt streams are predicted to occur with increasing air temperatures, which may impact future aquatic insect survival in these streams. We hypothesized that stonefly (Plecoptera) naiads from glacier-melt stream sites acclimated to different salinity levels would differ in survival, median lethal concentrations, and chloride cell responses to salinity. We conducted field bioassays in remote glacier-melt streams in southwestern China in 2015 and exposed representative aquatic stonefly naiads (Chloroperlidae, Nemouridae, Taeniopterygidae) from stream sites with different conductivity levels to experimental conductivity levels ranging from 11 to 20486 µS/cm for up to 216 hours. We then examined survivorship, calculated the median lethal concentrations, and measured chloride cell responses with scanning electron microscopy. Chloroperlidae survival after 120 and 216 hours did not differ (P > 0.05) among salinity treatments. Nemouridae/Taeniopterygidae survival after 120 hours did not differ (P > 0.05) among treatments, but after 216 hours survival was the least (P < 0.05) in salinity treatments with > 4600 µS/cm. Taeniopterygidae survival after 120 hours was the least (P < 0.05) in salinity treatments > 16,349 µS/cm. Median lethal concentrations did not differ among families. Chloroperlidae caviform cell number, density, and area decreased (P < 0.05) with increasing salinity. Taeniopterygidae caviform cell count decreased (P < 0.05) with increasing salinity, but cell density and area did not. Chloroperlidae and Taeniopterygidae coniform characteristics and Nemouridae bulbiform cell characteristics were not affected by salinity. Our results suggest that Chloroperlidae, Nemouridae, and Taeniopterygidae from glacial-melt streams in China may be able to tolerate increases in conductivity up to nine days.