Study On The Culture Environment And Phytoplankton Community Structure Of Scallop Culture Area In Laizhou Bay And Sishili Bay

The survey was conducted in the 7 scallop culture areas of Laizhou Bay and Sishili Bay from May to November in 2016~2017,to found out the environmental quality of the Yantai main scallop culture area.We investigated the entire cycle of scallop culture to fully mastered the quality of seawater during the growth of scallops.The physical and chemical indicators tested include water temperature,pH value,dissolved oxygen,salinity,chemical oxygen demand,inorganic nitrogen(ammonia nitrogen,nitrate and nitrite),total nitrogen,active phosphorus,total phosphorus and sulfide.Using organic pollution index and comprehensive evaluation of environmental condition to analysis the quality of seawater.The ecological diversity of the culture environment and the stability of the community structure were analyzed by identifying the species composition of phytoplankton,and the main environmental factors affecting the growth of phytoplankton in the relevant sea area were determined by canonical correspondence analysis.All indicators were tested in accordance with the methods specified in the Marine Monitoring Code.The survey results are as follows.The changes of water temperature and salinity ranged from 8.43 to 28.71°C and29.12‰to 31.61‰,both of which met the growth requirements of scallops.The changes of pH and chemical oxygen demand ranged from 7.85 to 8.29 and 0.13 to 2.76 mg/L,which met the Class I and II standards for seawater quality.Dissolved oxygen and sulfides ranged from 6.09 to 9.65 mg/L and from 0.0010 to 0.0312 mg/L,met Class I water quality standards.The changes of ammonia nitrogen,nitrate and nitrite ranged from 0.0020 to0.2663 mg/L,0.0080 to 0.3212 mg/L and 0.0007 to 0.0542 mg/L.The ammonia nitrogen and nitrate content in the individual months of Sishili Bay exceeded the standard,and other indicators met Class II water quality standards.The changes of inorganic nitrogen and dissolved inorganic phosphorus ranged from 0.0100 to 0.6340 mg/L and 0.0003 to0.0316 mg/L.The individual months of the Sishili Bay exceeded the standard,and the rest met the Class II water quality standards.The total nitrogen and total phosphorus ranged from 0.2490 to 1.0600 mg/L and 0.0060 to 0.1725 mg/L,and exceeded the standard in the partial months of Laizhou Bay and Sishili Bay.So we should control of sewage discharge.The organic pollution index of seawater ranged from-1.225 to 1.532.In May,June and October 2017,there were organic pollution conditions.Although the pollution level was low,it was necessary to strengthen the control of land contaminant input and aquaculture scale.The eutrophication phenomenon in Laizhou Bay and Sishili Bay was relatively serious in October and November,and had a certain relationship with the culture of scallops.The comprehensive evaluation of environmental quality showed that the seawater quality of Laizhou Bay and Sishili Bay are both Class I and II,and the water quality is suitable for the cultivation of scallops.The variation of phytoplankton density ranged from 0.33×10~4to 111.22×10~4cells/L,which could meet the demand of scallop feeding.The phytoplankton species were richer and more evenly distributed,so the community structure was relatively stable.The main influenced factors of phytoplankton community structure in Laizhou Bay were water temperature and nitrogen nutrient salt,and the main influenced factors in Sishili Bay were water temperature,salinity and phosphorus nutrient salt.In summary,the seawater environment of Laizhou Bay and Sishili Bay was suitable for the cultivation of scallops.But we should pay more attention to the control of sewage input and aquaculture scale,and reducing the input of pollutants such as nitrogen and phosphorus.Accord this way,we can prevent the occurrence of organic pollution and eutrophication,thus ensuring the sustainable development of the marine economy.