The Ecological Study Of Macrobenthos In The Bohai Sea, China

The ecological study of macrobenthos in the Bohai Sea was conducted in fourcruises during June2011, November2011, May2012and November2012, based onsamples of macrobenthos and sediment. The present study analyzed abundance,biomass, species composition, community structure, biodiversity and secondaryproduction, relationships with environmental factors and comparison with historicaldata of macrobenhos. This was a comprehensive study about the ecologicalcharacteristics of macrobenthos and changes of the macrobenthos community in thelast50years.A total of521species of macrobenthos were identified. The average abundancewas2668.13ind./m2and the average biomass was19.18g/m2. The average abundanceof spring cruises was significantly higher than that of autumn cruises while theseasonal comparison of the average biomass was just the opposite of the abundance.The higher value areas of macrobenthic abundance were located at northern LiaozhouBay, southern Bohai Strait and northeast Bohai Bay, while the lower value area waslocated at the waters near Yellow River estuary. In Bohai Sea the macrobenthicabundance increased with the sediment sand content and macrobenthic biomass hadsignificant negative correlation with organic matter content. Compared with thehistorical data, abundance has increased significantly and the biomass slightlyincreased from1959to1999, while displayed a declining trend after the21century.Remarkably different with some previous studies, polychaetes were absolutelydominant in the species number, abundance and biomass. The species compositionand community structure had showed an obvious―miniaturization‖trend. Theoriginally dominant Echinodermata and large Mollusca species were firstly replace bythe smaller Mollusca species. After21century smaller Mollusca species were furtherreplaced by polychaetes species, which were much smaller in body size. The water environmental factors affected the community structure significantly and the secondlyinfluential environmental factor was water content of sediment. The causes of thechange in community structure and―miniaturization‖trend are possibly overfishing,trawling, local pollution, eutrophication, change of predator species, and long-termnatural environmental changes.The overall mean of Shannon-wiener diversity index was4.34; the overall meanof richness index was10.84; and the overall mean of the evenness index was0.75.Chlorophyll a and pheophytin a were negatively correlated with macrobenthicbiodiversity probably because the filter-feeding habits of the bivalve speciescontrolled the content of chlorophyll in the waters.The mean value of the secondary production was6.52g (AFDW)/(m2×a) and7.91g(AFDW)/(m2×a) in2011and2012respectively. The mean value of P/B ratiowas2.77in2011and2.56in2012. The secondary production was relatively higher incentral Bohai than other areas in Bohai and that was probably because more foodsettle to the bottom consequently supported a higher secondary production. Thesecondary production was lower in waters near Yellow River Estuary than other areasin Bohai because the pollution was more serious and the sand content in the water wasvery high hence blocking the photosynthesis of the marine organisms. The estimatedtotal annual secondary production was2.8011Mt (wet weight) in2011and3.394Mt(wet weight) in2012.