Snail herbivory on submerged macrophytes and nutrient release: Implications for macrophyte management

Abstract

Radix swinhoei (H. Adams) is a freshwater snail commonly found in shallow regions of Lake Taihu. This research estimated, based on experiments, the consumption rates of R. swinhoei on three young submerged plants ( Vallisneria spiralis, Hydrilla verticillata and Potamogeton malaianus) and its rates of nutrient release. Results showed that the snails consumed V. spiralis at the highest rate (23.34 mg g −1 d −1), P. malaianus at a lower rate (11.97 mg g −1 d −1), and H. verticillata at the lowest rate (7.04 mg g −1 d −1). The consumption rates on V. spiralis varied significantly, with snail size, ranging from 13.63 mg g −1 d −1 for large-size snails to 143.42 mg g −1 d −1 for small-size ones. The average nutrient release rates of snails grazing on different macrophytes were 45.93 μg PO 4-P and 0.58 mg NH 4-N g −1 d −1. The food species had a significant effect on NH 4-N release rates but not on PO 4-P. However, the snail size had a significant effect on PO 4-P release rates and not on NH 4-N. The present study indicates that through selective grazing and nutrient release, snails may impose a significant impact on the macrophyte community, which should be considered in managing the macrophytes of a lake.