Tuesday, May 27, 2008

Influence of Catchment Land Use on in Situ Growth Rates of Elimia cahawbensis (Gastropoda: Pleuroceridae) in Headwater Streams of the Cahaba River Basin, Alabama USA

Lori R. Tolley-Jordan, Hayleigh Barlar, and Alexander Huryn. Department of Biological Sciences, The University of Alabama, Box 870206, Tuscaloosa, AL 35487

In situ growth rates of Elimia cahawbensis were quantified in eight headwater streams draining catchments with varying levels of urban land cover (0-60% urban cover). The catchments were of similar size, geology and canopy cover. Among the streams, four had one or more species of Pleuroceridae, while pleurocerid snails were absent in the remaining study streams. In February 2006, enclosures (clear PVC, 5 cm x 15 cm) were placed in 5 riffles per stream. One month later, 5-marked snails were randomly placed in each of 4 of the enclosures per stream (n=160 snails). The last enclosure contained no snails was used to estimate food availability (i.e., ungrazed algal biomass). Conductivity, pH, and dissolved oxygen were measured weekly and water temperature was measured hourly for all streams. Algal biomass (Chlorophyll a) was determined for each chamber at the end of the study. Instantaneous growth rates (g d-1) were calculated for each enclosure. No significant differences were found for snail growth rates, conductivity, pH, dissolved oxygen, temperature, or algal biomass among streams. This suggests that water chemistry associated with catchment-scale land use may not be the primary factor influencing the occurrence of pleurocerid snail populations in streams of the Cahaba River Basin.

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