The Ecological Effects Of Reclamation Activities On Macrobenthic Communities In Bohai Sea

In recent years,the discrepancy of limited land areas and huge demand for the land has become a serious issue due to the rapid development of the economy and growing population.Reclamation was regarded as one of the most straightforward solutions to tackle this problem.The economic circle around the Bohai Sea is the most developed region in the north of China,where the reclamation activities was carried out widely in the past years.Among these projects,the Caofeidian reclaimed area was the most typical one and the Longkou artificial island was one of the largest artificial islands in this region.This study aimed to analyze the spatial-temporal changes of macrobenthic communities under the disturbance of reclamation in the south of the Bohai Sea based on the field data collected in October 2013 and April,August 2014,respectively and the historical data.Meanwhile,the effects of reclamation on economic species and their adaptive mechanism were also studied by simulating the suspended particles and burial effects induced by reclamation projects in laborary.The main conclusions were as follows:1.The data collected in October 2013 were adopted to analyze the status of macrobenthic communities in the south of the Bohai Sea.The macrobenthic communities showed significant differences among Bohai Bay,Laizhou Bay,and Yellow River Delta while there are no significant difference between the reclamation region and other regions in Bohai Bay and Laihzou Bay.Besides,the health status of communities in the Bohai Bay was worse than that of the Yellow River Delta and Laizhou Bay.As for the temporal changes of the communities in the south of Bohai Sea,the dominant taxa group have changed from Crustacea and Mollusca to Polychaeta from the 1950 s to the 2010 s.The dominant species also shifted from economic species of Mollusca and Crustacea with a large body,long life span,and competitive ability to opportunity species of Polychaeta and Crustacea with a small body size,short life span,and uncompetitive ability.The health status of communities was getting worse,and the communities presented with a fragile and unstable status,which were dominated by opportunity species with small body size in the 2010 s.2.The spatial differences of macrobenthic community in Bohai Bay were analyzed based on the data in 2013.The species number and biodiversity indices were lower in sites closed to reclamation projects compared to that in sites a little far from reclamation projects.The sites in the southwest were affected seriously evidenced by the lowest values of species number and biodiversity indices appeared there.The communities with lower biodiversity and worse health status accorded well with the highest reclamation areas in the year.Surveys were conducted from 2010 to 2013 to investigate the influence of Longkou Artificial Island construction on macrobenthos.The environmental parameters of sediment,seawater,and communities changed significantly: the oil content in sediment,the concentration of suspended materials,and salinity of seawater all increased to some extent.The communities showed a miniaturization trend in body size and homogenization trend in species composition.The dominant species shifted from Polychaeta species in 2010 to Mollusca species with small body size in 2013.The health status of communities underwent different changes trend due to the distance to the artificial island,getting worse in sites close to the artificial island,and getting better far from the artificial island.3.The suspended materials induced by reclamation activities greatly impact the early development stage of key species then followed by the population recruitment.High concentration of suspended solid caused acute toxicity to the Thais clavigera larvae.A linear negative relationship between the survival rate and the turbidity of the water was identified.The survival rate decreased with the increasing exposure time to the suspended materials.However,the significance of the correlation between survival rate and turbidity declined by the continued increasing exposure time of larvae to the suspended materials.4.The burial effects induced by reclamation also impact the behavior and physiology of economic species varied with the burial depth and sediment grain size.Below 30 cm burial depth,Gomphina aequilatera showed a good vertical movement ability and high tolerance to the burial effects.The adding of the silt and the increase of burial depth have caused seriously oxidative stress and even increased mortality of the animals.Below 30 cm burial depth,the activities of antioxidant enzymes,superoxide dismutase(SOD),and catalase(CAT)of the animals showed significant up-regulation response.In the silt-adding burial groups,the quality of pore water in the central and bottom layers were getting worse by lower p H,higher NH4+-N concentration and more dead individuals were represented.5.A significant community succession was observed in the south of the Bohai Sea.The reclamation activities have accelerated the recession process of the community.The suspended materials and burial effects caused by reclamation projects also had adverse effects on the survival rate of larvae followed by the population recruitment.However,reclamation was just one of many causes to explain these changes of communities due to the complexity of the marine ecosystem and the diversification of influence factors.Several rivers are flowing into the Bohai Sea,especially the Yellow River,which unload a huge amount of silt to the sea.Besides,the increase of oil exploitation,mariculture,fishing,and trawling coupling with the increase of the temperature of seawater as a result of global warming also have caused influence on the macrobenthic communities.Therefore,the succession of the macrobenthic communities in the south of the Bohai Sea was triggered by the above multiple effects of global warming and anthropic activities.However,the drastic reclamation construction inevitably aggravated the degradation and succession process of the community.