Size Distribution and Nutrient Excretion ofMelanoides tuberculatain a Southern Nevada Spring Ecosystem

Abstract

To better understand the impact of Melanoides tuberculata on ecosystem processes via nutrient recycling, we quantified the body size distribution, density, and ammonia-nitrogen (NH4-N) and soluble reactive phosphorus (SRP) excretion of M. tuberculata in Rogers Spring, which is located in southern Nevada. We examined how nutrient recycling rates were related to body size and body nutrient content. We found that small individuals dominated the size structure, density, and NH4-N and SRP excretion rates and that nutrient recycling was determined by biomass rather than by high per capita excretion rates. The NH4-N excretion rates of M. tuberculata are between 2 and 27 times higher than the SRP excretion rates in Rogers Spring. These results indicate that M. tuberculata in Rogers Spring may be P limited and rather conservative in P recycling. In contrast to stoichiometric predictions, body nutrient content was a poor predictor of excretion rates. However, there was a close correlation between the measured and modeled NH4-N:SRP recycling ratio (NH4-N:SRPr), which suggests that diet N:P is more important in predicting NH4:SRPr than body elemental composition. Assuming that all excreted nutrients enter the water column, we determined that M. tuberculata contributes 17.3 mg N m-2d-1 and 3.3 mg P m-2d-1 to Rogers Spring. Although densities of M. tuberculata in the spring brook were lower than those reported in other studies, we assume that these exotic snails can have a significant impact on ecosystem processes, especially by N recycling in systems with very low ambient nutrient concentrations.