Density, but not distribution pattern of Assiminea latericea varies on tidal flats with smooth cordgrass Spartina alterniflora invasion stage

The effect of Spartina alterniflora invasion stage on density and distribution pattern of Assiminea latericea was studied in 2014 and 2015 on the coast of the Yellow Sea, Jiangsu, China. Invasion of S. alterniflora altered the environmental properties. With the increase of invasion age, the coverage and stem density of S. alterniflora and organic matter content tended to increase, whereas chlorophyll a and salinity tended to decrease. Using principal components analysis (PCA), the habitats were separated along the gradient of the invasion stage of S. alterniflora. Coverage and stem density of S. alterniflora and salinity were the most important characters for habitat differentiation because the PCA biplot illustrated that the vectors of these environmental properties involved the smaller angles with PC 1. Based on a two-way ANOVA analysis, invasion stage of S. alterniflora and season significantly affected the density of A. latericea (p < 0.001), but their interaction was not significant (p = 0. 226). The density of A. latericea varied significantly among seasons in each habitat based on a one-way ANOVA analysis, except in the bare mudflat without invasion. The highest densities occurred at the mature invasion stage in autumn, whereas the lowest densities occurred with no invasion in spring. Both Taylor's and Iwao's regressions indicated that A. latericea presented an aggregated distribution pattern (p < 0.001). The consistent distribution pattern indicated that it might be a biological trait of the species. Based on stepwise regression analysis, stem density of S. alterniflora and organic matter content were selected for the optimal regression model. Our results suggest that S. alterniflora invasion altered the environment of the coast and variation in A. latericea density was a response of the species to the environmental change caused by S. alterniflora invasion. Food resources, temperature, biological traits, and predation risk should be comprehensively considered. (C) 2019 Elsevier B.V. All rights reserved.