Effect of spatial distribution of sedimentary environment on macrobenthic community in spring season in Isahaya Bay, Japan

In order to assess the relationship between the macrobenthic community and the sedimentary environment in Isahaya Bay, Kyushu, Japan, we conducted field surveys at 9 sampling stations in April 2014. Based on clustering analysis of abundance of the macrobenthic community, the 9 sampling stations were clearly divided into three groups(Groups A–C). The groups A–C were located at the outer(3 stations), center(2 stations), and inner(4 stations)parts of Isahaya Bay, respectively. Group A had low mud content(28.3±10.8%, mean±standard deviation)with low total organic carbon(TOC) (14.2±4.1 mg C g−1)and low acid volatile sulfur(AVS, 0.12±0.1 mg g−1). The dominant species in group A were a deposit- and filter-feeding amphipod, Photis longicaudata; a suspension-feeding bivalve, Veremolpa micra; and an omnivorous polychaete, Scoletoma longifolia. Group B had high mud content(74.6%)with high TOC(19.1 mg C g−1)but low AVS(0.20 mg g−1). The dominant species of this group was V. micra; a deposit-feeding bivalve, Theora fragilis; and a deposit- and filter-feeding amphipod, Ampelisca brevicornis. Group C had high mud content(87.8±4.8%), TOC(21.4±2.9 mg C g−1), and AVS(0.85±0.5 mg g−1)and was dominated by a deposit- and filter-feeding amphipod, Monocorophium sp.; T. fragilis; and a carnivorous polychaete, Glycinde sp. These results suggest that the distribution of macrobenthos corresponds with the sedimentary environment gradient in Isahaya Bay.