Meeting Abstract

P3.116  Saturday, Jan. 5  Do Stream Pools Act as Sinks for Passively Transported Larvae? SCHAMEL, Lindsay B.*; FINGERUT, Jonathan T.; Saint Joseph’s University; Saint Joseph’s University ls413138@sju.edu

The non-swimming larvae of the black fly (Simulium tribulatum) are dependent on fluid-mediated dispersal to reach new habitats in response to conspecific competition, predation, and inadequate food supplies. While larvae have been shown to prefer regions of fast flow for protection from predators and increased flux of food, their ability to reach such areas is often dependent upon the transit of slow-flowing pools with unsuitable conditions. It has been proposed that pools may act as larval sinks as the slow, calm flow causes larvae to quickly drop out of suspension and limits their resuspension, thereby discontinuing downstream movement. In this study we test the hypothesis that dispersing larvae act as passive particles and that it should therefore be possible to predict their movement through a pool based on larval size. Fall velocity, one of the main factors influencing particle transport, was measured for a range of larval sizes both with and without the presence of silk threads. These threads have been shown to affect the ability of larvae to settle in preferred fast-flow, and may influence their fall velocity. Fall velocities were found to increase with size while the efficacy of silk threads decreased with size. Predicted dispersal distances were tested in a natural stream pool using settlement plates along a streamwise transect with a known, consistent velocity. Decay rates of larvae agreed with predictions that larger larvae would travel shorter distances before being trapped on the substrate as compared to smaller larvae. This data corroborates previous research that showed smaller larvae have greater success at transiting stream pools and that pools may act as sinks for dispersing larvae, particularly older and larger individuals.