Diadromous Neritid Gastropods: Examining How Water Velocity, Distance from Ocean, and Location on Substrate Shape Stream Communities

The species composition, size distribution and abundance of diadromous neritid gastropods were studied in two coastal streams on Mo’orea French Polynesia, from October to November 2010. Five species of the family Neritidae were examined: Neritina auriculata Lamarck, Neritina canalis Lamarck, Neritina turrita Gmelin, Clithon spinosa Budgin, and Septaria porcellana Linnaeus. Sampling occurred at increasing distances from the ocean. Water velocity, depth, and shell height was measured, location on substrate was recorded for each species, and comprehensive site surveys were conducted. Species composition changed at increasing distances from the ocean, with percentages of Neritina canalis increasing when moving upstream in the Amehiti River and percentages of Neritina auriculata decreasing when moving upstream in the Uufau River. Average shell heights were larger in upstream reaches and smaller in downstream reaches. Abundances of neritids decreased at water velocities greater than 0-2 m/s. Neritina auriculata and Neritina canalis were both found on the sides and bottoms of substrate.