Micro-distribution of Four Species of Neritid Gastropods in an Upper Mangrove Area, Ishigaki Island, Japan

Abstract

Multiple neritid species co-occur in tropical and subtropical estuaries. To demonstrate their micro-distribution patterns, the abundances of Neritina turrita, N. plumbea, N. auriculata and Clithon corona were surveyed in an upper mangrove area in Ishigaki Island by setting a 28 m² sampling area. Numbers of individuals were recorded in 25-cm grid positions in January and July 2006. Examinations of Moran's I coefficients showed the presence of positive spatial autocorrelations for all four species in both months. The conditional autoregressive model, a type of generalized linear mixed model, was applied to the abundance data with substrate depth from the high tide level as a fixed effect and spatial random effect. Model evaluation and coefficients of parameters demonstrated interspecific and temporal variations in the distribution. The effects of depth on the patterns of distribution were significant but were overridden by the effects of the spatial autocorrelation except for N. turrita in January and N. auriculata in July. Without considering spatial autocorrelation in the distribution, estimates of the abundances of neritid species in mangrove areas may be erroneous.