Meeting Abstract

P3.119  Saturday, Jan. 5  Larval settlement in benthic environments: The effects of velocity and bed geometry FINGERUT, J.T.*; THOMSON, J.R.; HART, D.D.; Saint Joseph’s University; Monash University, Australia; University of Maine jfingeru@sju.edu

Many benthic invertebrates have complex life cycles in which dispersal processes play a critical role in determining patterns of distribution and abundance. Near-bed flow patterns can affect both the suitability (i.e., effects on fitness) and accessibility (i.e. probability of settlement) of benthic habitats, so it is particularly important to examine their effects on settlement and dispersal. For example, boundary layer separation over an irregular bed can create two distinct regions of near-bed flow (i.e., accelerating flow over the forebody and a zone dominated by slower eddies over the aftbody) that may have different effects on larval settlement. We manipulated flow over convex roughness elements (i.e., hemicylinders) and examined how the settlement of stream insect larvae, the black fly Simulium tribulatum, varied with near-bed velocity and location within the substrate. Settlement rate of these larvae was standardized to correct for variations in larval supply (i.e., among-trial differences in the concentration of larvae in suspension). Our analysis showed that position on the hemicylinder and near-bed velocity both affected settlement rate, with a strong interaction effect. Specifically, the observed relationship between settlement rate and velocity was negative on the forebody and positive on the aftbody. We explore these contrasting results by considering various physical and behavioral mechanisms that could potentially influence such patterns. The results are consistent with a simple graphical model that focuses on how near-bed velocities affect the time required for larval contact and attachment.