Macrobenthos Communities Under Different Habitat

Macrobenthos is an important fishery resource. With the rapid development of economy, the macrobenthos are affected by pollution,causing substantially reduced its community structure change and biodiversity; this study was at Fukushima-cho, Japan, we use the sledge net of ushio maru, Hokkaido University, try to do a survey (May and November) to find the amount of macrobenthos resources, especially the amount of crustaceans and bivalves around the Fukushima-cho and analyzed fish effects on water nutrient concentrations and phytoplankton communities.(1) In May and November174species of macrobenthos were collected, density and biomass in May were1402.5inds./m2and691.5g/m2, the density and biomass were925.5inds./m2and1294.5g/m2in November, diversity index H and J were0.92±0.18and0.72±0.14, the dominant species were Themisto japonica, Euphausia pacifica, Pleustes panopla, Stenothoe sp., Spirontocaris sp. and Laqucus nubellus.(2) Two times we collected Crustaceans85kinds, the density of May and November were1188inds./m2and703.5inds./m2, biomass were163.2g/m2and47.8g/m2, the main species were T.japonica and E.pacifica. And the density of Echinodermata in May and November were74.1inds./m2and106.2inds./m2, biomass were318.8g/m2and474.6g/m2, the main species were Amphipholis kochii, Grossaster papposus, Plazaster borealis and Temnopleurus hardwickii. Two times were identified4kinds Brachiopoda, Brachiopoda density and biomass were78.7inds./m2and279.4g/m2in May and125.4inds./m2and763.3g/m2in November.(3) The water temperature, salinity were positively correlation with the density of T.japonica, E.pacifica and negatively correlated with the density of Pl.panopla, Stenothoe sp., Spirontocaris sp., and L.nubellus. The water depth had a negative correlation with the density of L.nubellus. Asteroidea, Echinoidea negatively correlated to distance and depth of the water. The density of fish affected by the density of Amphipoda, tend to be distributed in nutritious waters. Temperature and depth were the major factor to affect the distribution and number of Fukushima-cho macrobenthos in this experiment.(4) Results showed that after adding bitterling R. sinensis, water nutrient, i.e., total nitrogen, ammonia nitrogen and total phosphorus concentrations obviously increased, water quality deteriorated from Grade II to exceeded Grade IV, and twelve fish group showed a higher effect. Phytoplankton community structure presented some change, i.e., biodiversity decreased, while density and biomass significantly increased. Two treatments with bitterling fish were dominated by large-bodied Chlamydomonas, and the control group dominated by small-bodied Kirchneriella. Therefore, as dominant fish of clear water, excessively high bitterling population density would result in the increment of both water nutrient concentrations and phytoplankton biomass, become the potential danger of water quality deterioration.