The Ecologic Investigation On Macrobenthic Communities In Intertidal Zone Of The Yangtze River Estuary

The wetland of the Yangtze estuary is one of the fifty most sensitive areas to the global climate change. The macrobenthic communities are important dynamic center in the wetland ecosystem of the estuary tidal zone. The changes of macrobenthic communities biodiversity and spatial distribution often influent primary producer and consumer populations. In addition, macrobenthic communities regulate ecological functions of estuary ecosystem. For example, the population fluctuations of the marobentic communities influences many important physical, chemical and geologic processes, such as the stability of sediments and transfer. In order to fully understand the functions of macrobenthic communities to wetland ecosystem of tidal zone and to understand the utilization of the estuary wetland, the community characters of macrobenthic communities should be extensively studied. In this present study, the distribution of macrobenthic communities and the influent factors in the Yangtze estuary intertidal zone were investigated, including investigation of the macrobenthic community distribution in large scale, the environmental factors and residual toxicity in this area. The major conclusions of this research are listed as below:1. Macrobenthic community distribution chracter in the intertidal zone of the Yangtze estuary.This survey covers the main the pericontinental and islands intertidal zone of the Yangtze estuary, including Chongming Island, the main pericontinental zone of Shanghai City, Jiuduansha shoals and Beigangbei shoals.From June to October in 2006,21 sections were set for investigation of macrobenthic fauna in intertidal zone of Chongming Island. In this investigation, totally 72 species were collected, which belong to 41 families of 5 phyla. The density and biomass were 166.20ind/m2 and 99.28g/m2 in June,136.81ind/m2 and 83.04g/m2 in October. The biodiversity values of H', J and D were 1.851±0.528,0.306±0.098 and 0.622±0.141. The dominant species were Sesarma dehaan, Helice tientsinensis, Ilyrplax deschampsi, Corbicula fluminea, Glauconome chinensis, Assiminea latericea, Assiminea sp., Cerithidea largillierli et. al.. The altitude of intertidal zone is relatively high due to having not dike in Chongming Island for more then ten years. The hemi-terrestrial crabs in the upper intertidal zone were prosperous, which lead to the increasing total biomass in most sections. The biomass of Sesarma dehaan took 32.35% or 43.64% of total biomass respectively in June and October. According to the cluster analysis results, the macrobenthic communities could be divided to three groups, communities in south of Chongming Island, Chongming Dongtan wetland communities and communities in north of Chongming Island.The three areas are different in the salt, sediment and plants. In the south of Chongming Island, the species compositions of macrobenthic communities were simple. The biomass of Sesarma dehaani took more than half of total biomass. In the north of the isoland, the macrobenthic communities showed complicated compostions due to the brackish and fine sediments. Bullacta exarata and Moerella iridescens dominated the low mudflat. In the Chongming Dongtan region, due to fluctuated salt and coarse sediments, the macrobenthic species were also abundant.From May to July of 2007,8 sections were set in every month for investigation of macrobenthic fauna of Beigangbei shoals. The altitude of Beigangbeisha shoal is very low. It is higher than water only during spring tides. No vascular plant was distributed yet. Since lacking living and breeding area, the macrobenthic communities showed simple composition. Only 14 species were founded in the present study. The density was 0.25ind/m2, the biomass was 0.22g/m2, and the average biodiversity values of H', J, D and AMBI were 0.667, 0.667,0.255 and 1.122, respectively. The unstable sediment is not suitable for bivalves breeding, nor for survive of gastropoda. These data suggest that plant is extremely important to maintain macro benthic community diversity.In May, July, October and December of 2009,8 sections were set for macro benthic communities research in Jiuduansha shoals. The Jiuduansha shoal was the only island that has not been dike and utilized by human in the Yangtze estuary. It is reserved for migratory birds. The macrobenthic community composition was complex.82 species were collected, which belong to 49 families of 5 phyla. The density and biomass were 405.80ind/m2 and 87.70g/m2 respectively. In Jiuduansha shoal, vascular plants are widely distributed and macro benthic communities show complicated compositions. Salty varied seasonally. The abundance and biomass were lower in October 2009 than in other months, the migratory birds may prey too many macrobenthos. For example, Mactra veneyformis was abundance in east Jiuduansha, Nuttalia obscurata and Meretrix petechialis were found. The density was mainly controlled by Assiminea sp., Elachisina sp., Eohaustorius cheliferus and Glauconome chinensis; the biomass was controlled by Sesarma dehaani, Sinonovacula constricta, Potamocorbula ustulata, and Mactra veneyformis. In the intertidal zone of Jiangya South shoal, densely distributed Donacia frontalis were observed and it is the first time that this species was found distributed in the Yangtze estuary.From September 2006 to May 2007,31 sections were set in the pericontinental zone of Shanghai for macro benthic communities research. In this investigation, totally 67 species were collected which belong to 36 families of 4 phyla. The density and biomass were 712.81 ind/m2 and 123.44 g/m2 in spring,761.65 ind/m2and 115.63 g/m2 in autumn. The pericontinental intertidal zone was the most artificially influenced area in the present investigation, including dike and pollution. High intertidal zone was almost lost and only very narrow intertidal zone was rested. The vascular plants distributed zone was narrow, in which macro benthic community of the highest species number, biomass and biodiversity should be distributed. The decreasing intertidal zone led to that macrobenthos lose their habits especially in high interdidal zone, such as the hemi-terrestrial crabs. By contrast, macrobenthos species as Littorinopsis intermedia, Nerita yoldi, Crassostrea sp. and Balanus albicostatus are widely distributed.To conclude, the distribution of macrobenthos in the intertidal zone of the Yangtze estuary was related to altitude, salt, plant, contaminants, sediments. The intertidal zones of Chongming Island, the pericontinental zone of Shanghai City and Jiuduansha shoals have relatively higher altitude and salinity, and posses complete plant communities. In these areas, the macrobenthic species number, density, biomass and diversity index values are relatively higher. Whereas, the intertidal zone of Beigangbei shoals have low altitude and salinity, coarse sediments and lack vascular plant. Therefore, the values of macrobenthic communities in the intertidal zone of Beigangbei shoals are significantly lower other regions.2. Human activities and the distribution of macrobenthic communityFrom June of 2006 to December of 2009, totally 68 sections were set for investigation of macrobenthic fauna in intertidal zone of the Yangtze River estuary. Along each section,3 sample sites were set from the high to the low tidal zone and each section was sampled 2-4 times. In this investigation, totally 122 species were collected which belong to 71 families of 6 phyla. Arthropoda were the richest in species number, including 61 species of 32 families. 38 molluscas species were recorded, which belong to 26 families.18 annelid species were found, which belong to 10 families. Among the 122 total species,91 species which belong to 65 families were found distributed in soft-sediment area, as mudflats or sandflats.16 species which belong to 7 families were found only distributed in hard-sediment area. The species records are largely increased in number compared to the around 60 species of the history data. Some species without previous record were acquired in this investigation. Ellobium chinensis, Neritina violacea and Nuttalia obscurata were first record in the Yangtze rive. However some species with previous record were not acquired in this investigation. The species number increasing is mainly due to the increased sampling area in the present study.Residual toxicity in certain macrobenthic species was analysized.The results showed that concentrations of Zn, Cd, Pb and petroleum were highly accumulated in Sesarma dehaani of the Hangzhou Bay. The accumulations of heavy metals, Pb, Cd and As were high also in Chongming Island. Sesarma dehaani accumulated more heavy metals which are essential for life than those are unessential, for an example, the essential Cu and Zn is more accumulated than the unsessential Pb, Hg and As.The value of accumulation in Sesarma dehaani of petroleum, Cu, Pb, Cr, Cd and DDT, was high in Chongming Island. This showed that the pollution is severe in Chongming Island and is dangerous for migratory birds. Previous report showed that the Pb and Cd in Chongming Island and Pb in Jinshan was high in the mud snail. Compared with previous data, the accumulations of Pb, Zn and Cu in Dongtan wetland have been slightly increased. By contrast, the accumulations of Cu and Pb have been slight decreased. The value of residual toxicity display declined trend from Chongming Island, Fengxian, Jinshan, Baoshan to Nanhui.In September of 2004,2006 and 2008,3 sections and 15 sampling sites, totally 75 sample plots, were set up in intertidal zone of Nanhui district of Shanghai for qualitative and quantitative investigation of marobenthos. Ecological quantitative observation approaches were utilized in our present studies to evaluate the effects of diked wetland on macrobenthic communities. As conclusion, dike showed negative effect for macro benthic species, distribution and dominant species in long run. The macro benthic communities degenerate quickly, and Chironomid larve appeared and Chironomid community was even gradually formed in the pools. The concentrated distribution of macrobenthos was in tens of meters wide area between the bank and the groyne. On the underwater constructions lived some macrobenthos which never appeared in the mudflat or sandflat, such as Nerita yoldi.Spartina alterniflora invasion in the Yangtze estuary tidal flat affect ecology functions of Chongming Dongtan and Jiuduansha Island reservation area. Limit and reduce the distribution of Spartina alterniflora are necessary. In this experiment, Spartina alterniflora was removed by submergence. After the remove Spartina alterniflora, Phragmites australis resettled and during the plant recovery, a succession of macrobenthic communities was recruited. The results showed that the macrobenthic communities were simplified after the submergence, since macrobenthos survived only in the intertidal flats. However, Diptera larvae and Corophium sinensis are prosperous.