Effects of total dissolved solids on growth and mortality predict distributions of stream macroinvertebrates

Abstract

Summary Spatial distributions of many freshwater invertebrates are associated with the concentration of total dissolved solids (TDS) in streams (usually measured as specific electrical conductivity – EC). These patterns are presumably caused by taxon‐specific effects of TDS on the maintenance of ion and water balance, which is energetically expensive and thus could affect fitness. However, no studies have assessed if TDS‐related effects on fitness metrics, such as growth and survival, are predictive of distributions. We used stream‐side, flow‐through microcosms to experimentally determine how TDS concentration influenced three life‐history performance measures (growth, mortality and emergence) of 13 species of aquatic insects. We then modelled the relationship between experimentally derived performance measures and both EC optima and minima estimated from field surveys. In the streamside experiment, we exposed taxa to stream water with naturally low (<25 μS cm−1) and moderate (>125 μS cm−1) EC for 83 days, controlling for differences in habitat, temperature, food availability and pH. We measured performance as the differences in specific growth rates, survival and adult emergence between the two treatments. Treatment effects on performance varied among taxa and with performance metric. Survival differences between treatments varied from 1 to 21 days, and specific growth rates differed by 0.07–1.5 day−1. Emergence success was less variable (>20% for only two taxa). Three taxa performed better in the low EC treatment, six in the moderate EC treatment, one had a mixed response and three taxa did not differ between treatments. The best model predicting field‐derived EC optima included both survival and specific growth rate as predictors (R2 = 0.68). Estimates of EC minima were not as strongly related to performance measures as were optima estimates. Taxa with greater performance in the moderate EC treatment had the highest EC optima, indicating that low TDS concentrations could restrict the distributions of taxa adapted to higher TDS concentrations. In contrast to taxa with higher EC preferences, taxa that can tolerate low EC environments will likely be increasingly stressed as stream TDS increases in response to climate and land–use change expected this century.

Predicting combined effects of land use and climate change on river and stream salinity

“…The future EC predicted in 2100 indicates losses of an additional 42% of this habitat, for a total loss of 69% of low EC habitat in which most taxa evolved. Loss of these low EC habitats would stress the biota in these systems adapted to low salinity environments [32,33], leading to taxa losses, shifts in composition and potentially changes in ecosystem processes [34].…”

Suspended sediment and turbidity after road construction/improvement and forest harvest in streams of the Trask River Watershed Study, Oregon

“…[]). Even relatively small changes in suspended sediment concentrations (SSC) can adversely affect aquatic biodiversity, especially affecting species with a narrow range of suspended sediment tolerance [ Olson and Hawkins , ]. For this reason, regulatory agencies have been using criteria to regulate sediments in inland water bodies often using turbidity as a surrogate for suspended sediments [ US Environmental Protection Agency ( EPA ), ].…”

Geographical origin determines responses to salinity of Mediterranean caddisflies

“…Thus, it has been suggested that the ability of some invertebrates to tolerate dilute water may allow them to inhabit a wide range of water salinity. However, physiological mechanisms to overcome low water salinity likely evolve at the expense of other traits that are beneficial at higher water salinity conditions [11, 26,27]. According to this hypothesis, we expect that organisms adapted to low salinity will maintain similar levels of survival through different experimental salinity levels, but will reduce their behavioral performance at higher salinity as an expression of the costs of low-salinity adaptation.…”