| With the rapidly increase of culture scale and density,Changhai Japanese scallop industry faces a huge crisis.This experiment:(1)From February to November 2017,a survey of water quality monitoring was conducted in survey area.(2)The food source in the envernoment and digestion food of raft and bottom cultured Japanese scallops in Changhai were conducted.This study was aimmed at laying a foundation for the further and systematic study on Changhai County's marine environment,the change of food sources of Japanese scallop in Changhai County.The main results are as follows:1.During the experiment,the physical and chemical parameters of the surface and bottom water in the test area are as follows:water temperature 1.06 to 24.20°C,salinity 31.96 to 34.12,pH 8.23 to 8.39,and nitrate content 0.011 to 0.144.The content of nitrite was from 0.001 to 0.019 mg/L,ammonia nitrogen from 0.002 to0.057 mg/L,and phosphate from 0.002 to 0.011 mg/L.In winter,spring and autumn,there was no significant difference(P>0.05)between surface and bottom water temperature,with a range of 0.01 to 0.88°C.In summer,there was significant difference(P<0.05)between surface and bottom water temperature,with a temperature range of 0.79 to 1.53°C.In general,the bottom water salinity was higher than that of the surface water,and there was no big difference between the surface and bottom water salinity in the winter,spring and autumn.The difference of water salinity was 0.04 to 0.36,and there was significant difference(P<0.05)in summer,ranging from 0.43 to 0.56.There was no big difference between the surface and bottom water pH,the concent of nitrates,nitrites,ammonia nitrogen and phosphates fluctuate.2.During the experiment,the results showed a total of 49 taxa belonging to 3phyla were identified,Bacillariophyta(35 species)and Dinophyta(11 species)were the dominant phytoplankton groups and only 3 species belonged to Euglenophyta.The cell abundance of phytoplankton in pear month had a large variation:to the surface water,the maximum of cell abundance appearing in February was 19.81×10~4 cells/L and the minimum appearing in October was 1.67×10~4 cells/L.;to the bottom water the maximum of cell abundance appearing in February was 15.22×10~4 cells/L and the minimum appearing in November was 1.40×10~4 cells/L.The Shannon-wiener diversity index of the phytoplankton community in the surface and bottom water ranged from 0.595 to 3.933 and 0.476 to 3.673,with average values of 2.520 and2.500,respectively.The Pielou's evenness index of the phytoplankton community in the surface and bottom water ranged from 0.188 to 0.872 and 0.184 to 0.944,with the average values of 0.669 and 0.667.Compared with previous studies,the species number and cell abundance of phytoplankton in this area did not have large variation.But the content of Dinophyta increased a lot:Dinophyta was the dominant phytoplankton group in April and May in the surface water;Dinophyta was the dominant phytoplankton group in April in the bottom water.The relative contents of diatom and dinoflagellate fatty acid markers in the POM of surface and bottom water were relatively high,and the dinoflagellate was less fluctuating.The relative content of C18:4n3 in POM of surface water>POM of bottom water>sediment.The relative content of OBFAs was relatively low,and the POM of bottom and sediments were higher than the POM of surface water.The relative contents of brown and large green algae were relatively low.3.The fatty acid biomarkers of the digestive glands of Japanese scallops showed that diatoms,flagellates or protozoa were the main food source,followed by dinoflagellates,green algae,and brown algae,with minimal bacteria.The source of food for scallops depends largely on the availability of food in the environment.It may also had certain filter selectivity and preference for diatoms.Compared to the raft cultured scallops,the contribution of diatoms and flagellates or protozoa to the bottom cultured scallops was higher and stable. |
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