Tuesday, June 5, 2007
459

Habitat scale effects of flow velocity, depth and density on spat movement of a tropical snail

Kathleen R. Jennings1, M. Eric Benbow2, Mollie D. McIntosh2, and Albert J. Burky1. (1) Biology, University of Dayton, 300 College Park, Dayton, OH 45469-2320, (2) Entomology, Michigan State University, East Lansing, MI 48824

Diadromous invertebrates are common to tropical streams worldwide.  Several neritid snail species are known to form mass spat migrations from the ocean into freshwater habitats, with little known about environmental factors controlling movement or dispersal.  In 2001, we conducted manipulative experiments to understand flow and density effects on neritid spat movement and dispersal in two streams of different size on Maui, Hawaii.  Spat of Neritina granosa were collected, tagged with unique codes, and released into streams void of natural populations due to a diversion barrier.  Sequential recoveries determined the spatial dispersal and movement patterns of individual snails in relation to depth, velocity, Froude and distance to bank.  A second manipulation increased spat density by 5-fold in the large stream.  There were significant, but weak positive relationships between spat migration rate (m.d-1) and depth, surface velocity and Froude; however, specific relationships depended on density and stream size.  In the larger stream, we found increased migration rate variation in density treatments, with larger proportion of individuals recovered in low flow microhabitats closer to the bank.  In the small stream there were inverse relationships between migration rate and flow, probably due to significantly lower habitat velocity and shallower depth of the study reach.

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