Effect of Saltmarsh Cordgrass, Spartina alterniflora, Invasion Stage on Cerithidea cingulata (Caenogastropoda: Potamididae) Distribution: A Case Study from a Tidal Flat of Western Pacific Ocean, China

The effect of saltmarsh cordgrass, Spartina alterniflora (Poales: Poaceae) invasion stage on Cerithidea cingulata (Caenogastropoda: Potamididae) distribution was studied in 2007 at the eastern tidal flat of Lingkun Island, Wenzhou Bay, China. The distribution pattern of C. cingulata was aggregated during each season, as shown in experiments utilizing Taylor's power regression and Iowa's patchiness regression methods (P < 0.001). Two-way ANOVA indicated that densities were significantly affected by S. alterniflora invasion stage (P < 0.001), however, no significant season effect was found (P = 0.090) and on the interaction between the seasons (P = 0.939). The density distribution during the invasion stage was significantly different in each season as shown in one-way ANOVA. Pearson's correlation coefficient analysis of density data indicated that the highest densities occurred in habitats at the initial invasion stage during summer. The peak in C. cingulata density during spring, autumn and winter occurred in habitats where invasion was classified as initial, whereas the lowest densities occurred in the stage of invasion completed during each season. C. cingulata density distribution varied among different habitats, and such variation indicates the response of the species to environmental change, particularly S. alterniflora invasion.