Response of Diatom Community Structure to Silicate Enrichment in Sanggou Bay in Spring
Effects of silicate addition on phytoplankton abundance(characterized by chlorophyll a concentration),particle size structure and community structure were investigated in the mariculture area of Rongcheng Sanggou Bay in Shandong Province using on land-based enclosure in spring of May 2021,water temperature from 13.83℃to 16.96℃.The test unit with a volume of 100 L,which was fixed in a land-based enclosure with a length of 200 cm,a width of 160 cm,a height of 120 cm,and a volume of about 3 800 L,was separated by a straight transparent polyethylene,and divided into 3 groups with 3 replications each group:(1)natural seawater group:1.41 μmol/L SiO3-Si(control group);(2)low concentration group:20.00 μmol/L SiO3-Si(group LS);(3)high concentration group:100.00 μmol/L SiO3-Si(group HS).A total of 70 L of the surface seawater in Sanggou Bay was filtered by 200 μm sieve and pumped in the test units,and a small pumping pump of 2 W was equipped in each test unit to keep the seawater always in a mixed state and not exchange with the external water body for 7 d,and the silicate added was prepared by pure nonahydrate sodium silicate.Results showed that:(1)silicon enrichment improved phytoplankton chlorophyll a concentration,by the end of the experiment,the chlorophyll a concentration being increased by 95%in the group LS and by 94%in group HS compared to that in the control group,with significant differences in microphytoplankton and nanophytoplankton cell abundance.(2)The phytoplankton in seawater was primarily composed of diatoms,dinofacterium and green algae in spring,with a total of 44 species,including 34 species of diatoms,9 species of dinoflagacterium and 1 species of green algae,with dominate diatoms,accounting for about 77.27%of the species richness,followed by dinoflagellates.(3)During the experiment,the diatom cell abundance was changed from 0.96×103 cells/L to 1.62×103 cells/L.There was higher abundance of diatom cells in the HS group at the 7th d,with a mean value of 1.62×103 cells/L,from the 3rd day,significantly higher abundance of diatom cells in the HS group than that in the control group(P<0.05).By the end of the experiment,the diatom cell abundance was increased in the groups LS by 53.53%and in HS group by 69.77%compared to the control group.(4)Silicate enrichment has a significant effect on the growth of diatoms Cyclotella,Nitzschia closterium f.minutissim,and Thalassiosira rotula(P<0.05),with the most significant increase in the Nitzschia closterium f.minutissim abundance,increasing by 181.69%compared to the control group.(5)Silicate addition led to improve the species richness of phytoplankton community structure(P<0.05),without significant effect on phytoplankton diversity and evenness.The findings will provide basic data and valuable clues for the possibility of exploring silicon element supplementation strategies in key periods of aquaculture waters and developing phytoplankton primary productivity improvement technologies to improve the capacity of shellfish aquaculture.
silicatediatomscommunity structureparticle size structureSanggou Bay
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