Taxon-specific responses to high-flow disturbance in streams:implications for population persistence

This study examined how the leptophlebiid mayfly Deleatidium spp., the mudsnail Potamopyrgus antipodarum, and stony-cased caddisflies Pycnocentrodes aeris and Hudsonema amabilis, each with different flow habitat preferences and motilities, respond to elevated flows. Our aim was to learn more about how refuge-seeking behavior and life-history traits affect species persistence along the flow disturbance gradient. All taxa responded to incrementally increased flows in a recirculating laboratory flume with layered substrata by moving to deeper, more stable layers. However, snails made the most pronounced shift to protected sublayers. Caddisflies that remained on epibenthic surfaces during high flows laid draglines on surface rocks to effectively resist dislodgment. Very few individuals of any taxon were washed from epibenthic habitats by high flows alone. Simulated flash floods in artificial stream channels revealed that dislodgment was linked to substrate stability and that likelihood to be dislodged varied among taxa. Dislodgment was relatively low for mayflies and snails (∼8%) compared to caddisflies (20.7%) in stabilized patches of gravel. However, in unstable patches, dislodgment rates of both mayflies and caddisflies (both ∼30%) were significantly higher than those of snails. The relatively high dislodgment rate of caddisflies in both stable and unstable substrate patches was related to their propensity to occupy epibenthic surfaces. Mortality rates of mayflies (∼25%) were about 3× higher than those of the other 2 taxa in both patch types. Our results suggest that high dispersal capabilities seem particularly important for Deleatidium to persist in flood-prone streams, whereas short-term behavioral modifications play a key role in allowing the snails and caddisflies to persist in flow-variable habitats.