Effects of environmental factors on the density of three species of peracarid crustaceans in micro-tidal sandy shores in Japan

Abstract

The swash zone of sandy shores is a transitional habitat between the sea and land where the physical environment is the primary factor influencing the distribution of shore macrofauna. We constructed cumulative logit models using Bayesian inference to predict the ranked abundance of three species of peracarid crustaceans (Haustorioides japonicus, Excirolana chiltoni, and Archaeomysis kokuboi) that dominate the sandy shores of the Niigata coastline, Sea of Japan. Additionally, we estimated the importance of 14 environmental factors at explaining the variation in abundance. The environmental factors were grouped into three categories: swash zone, landward, and offshore. Optimum models were selected among the null model, the basic model (swash zone factors only), and additional models with landward and/or offshore factors. The optimal model for each of the three species was obtained when landward and/or offshore factors were added to the basic model, suggesting the importance of these regional factors. Combinations of significant factors differed between the three peracarid species. Some differences can be explained by accounting for life history characteristics. The slope of the offshore seafloor was the only common significant factor for the three species. Therefore, a decrease in the size of the shallow area off the sandy shore was associated with a decrease in the density of the three species. Because the peracarid crustaceans play an important role in trophic links in sandy shore ecosystems, our study results predict that an increase of coastal erosion leading to change of near-shore bathymetry will reduce the ecological function of the swash zone.