Role of microhabitat heterogeneity in benthic faunal communities in sandy bottom sediments of Oura Bay, Shimoda, Japan

• Benthic faunal community structures in a subtidal sandy bottom area were studied.
• The community structures differed among small-scale microhabitats.
• Sedimentary organic matter content also differed among microhabitats.
• The faunal abundances correlated with sedimentary organic matter content.

Habitat heterogeneity contributes to the maintenance of species diversity; however, little is known about the influence of microhabitat heterogeneity on the diversity of sandy bottom invertebrates. We tested the hypothesis that the structure of benthic faunal communities differs among microhabitats because each microhabitat function differs according to their physical properties. The descriptors of invertebrate assemblages (species richness, numerical abundance, and species composition) and physical properties (sedimentary organic matter content, sediment grain size, water temperature, and salinity) were determined monthly from April 2012 to March 2013 at 6 sampling stations (the stations were approximately 100–200 m apart) in the Oura Bay, Shimoda, Izu Peninsula, Japan. Species richness and numerical abundance of macrofauna varied significantly among stations, as well as the species composition. There were also significant differences in sedimentary organic matter content and grain size among the different stations. These results suggest that faunal distribution and environmental properties can differ at the microhabitat scale. Furthermore, multiple regression analysis revealed that a significant positive correlation existed between the sedimentary organic matter content and numerical abundance and, consequently, sandy bottom faunal communities were structured depending on the sedimentary organic matter content at the microhabitat scale. A diverse benthic faunal community is formed owing to the heterogeneity of microhabitats in sandy bottom sediments; thereby, further studies are required to characterize microhabitat differences.