Monday, May 26, 2008 - 4:30 PM
104

Influence of grazing snails on stream ecosystem processes: Seasonal patterns in growth, respiration, and nutrient excretion

Brian J. Roberts, Louisiana Universities Marine Consortium, Defelice Center, 8124 Highway 56, Chauvin, LA 70344, Walter R. Hill, Institute of Natural Resource Sustainability, University of Illinois, 1816 S. Oak Street, Champaign, IL 61820, and Patrick J. Mulholland, Environmental Sciences Division, Oak Ridge National Laboratory, Bethel Valley Road, PO Box 2008, Oak Ridge, TN 37831-6036.

The snail Elimia clavaeformis (density = 1500 per m2) is the dominant grazer in Walker Branch accounting for ~95% of invertebrate biomass in the system.  Previous studies have demonstrated that despite high periphyton production rates during the open canopy spring, biomass is maintained at low levels by intense grazing by Elimia.  We examined seasonal patterns in snail growth, respiration, and nutrient excretion for multiple size class of Elimia over three years to better understand their contributions to ecosystem processes in the system.  Snail specific growth rates are highest in the open canopy spring (increasing with periphyton production rates) and lowest during summer.  Snail respiration exhibits a distinct seasonal pattern with the highest rates occurring when organic matter availability is highest (during spring algal bloom and leaf fall in autumn).  Snail R contributes significantly to ecosystem R (2.5 - 8.5%) with the highest contribution occurring in summer.  On a yearly basis, respiration scaled with body size as predicted by metabolic theory, but the influence of varying food quality was seen seasonally.  Snail N and P excretion also peaks in spring and autumn peaks and during baseflow can account for over 60% of NH4+ and up to 10% of SRP in streamwater.


Web Page: snails, respiration, nutrient excretion

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