Effect of Eutrophication on the Structure of Meiobenthic Communities in Hiroshima Bay

Abstract

ITAOKA, MUTSUMI and KYOICHI TAMAI (Nansei National Fisheries Research Institute). 1993. Effect of eutrophication on the structure of meiobenthic communities in Hiroshima Bay. Benthos Research, 45 : 19-28.
Meiobenthos was surveyed to investigate the relationship between its community structure and eutrophication of the bottom sediment at three stations in Hiroshima Bay throughout the year. The organic content of sediments was high at all these stations, namely about 14% in ignition loss and 2.3-2.6 mg/g dry sediment in total nitrogen content. At the innermost station, total sulphide concentration was 1.6 mg/g dry sediment in average, which was 3.6-5.6 times higher than at the other stations. The oxygen concentration in the bottom water was also fairly low (range : 1.6-2.9 ppm) from June to September at the station. The abundance of meiobenthos was highest at the innermost station, being about twice as much as that at the outermost station. Except at the outermost station, the abundance increased from spring to summer and decreased in September. Nematodes comprised more than 85% of the total meiobenthos at all stations, with the highest abundance occurring at the innermost station. Harpacticoids were most abundant at the outermost station. The nematode/copepod ratio was highest at the innermost station, and lowest at the outermost station. Most harpacticoids occurred in the top centimeter of sediment. Nematodes inhabited at least down to 5 cm, but they tended to occur more in the surface layer at the innermost station. It is suggested that stressful bottom conditions such as low oxygen concentrations and high total sulphide caused change of meiobenthic community structure.