春季桑沟湾硅藻群落结构对硅酸盐加富的响应研究

Response of Diatom Community Structure to Silicate Enrichment in Sanggou Bay in Spring

2021年5月,在水温13.83~16.96℃下,用现场陆基围隔实验方法研究添加硅酸盐对山东荣成桑沟湾养殖海区浮游植物丰度(以叶绿素a浓度表征)、粒径结构以及群落结构的影响。体积为100 L的直筒型透明聚乙烯袋围隔而成的实验单元,设置3个处理组,每组三个平行:自然海水组1.41μmol/L SiO_(3)-Si(对照组);低浓度组20.00μmol/L SiO_(3)-Si(LS组);高浓度组100.00μmol/L SiO_(3)-Si(HS组);取桑沟湾近岸表层海水70 L,经200μm筛绢过滤后注入实验单元,每个实验单元中均配置2 W的小型抽水泵,保持海水始终处于混匀状态,不与外部水体交换,添加的硅酸盐为分析纯九水硅酸钠,并固定在长200 cm、宽160 cm、高120 cm,容积约3 800 L的陆基围隔中,实验持续时间7 d。结果显示:(1)添加硅酸盐可提高浮游植物叶绿素a浓度,LS组和HS组叶绿素a浓度分别是对照组的1.95倍和1.94倍,主要是小型浮游植物和微型浮游植物的叶绿素a浓度显著提高;(2)硅藻是浮游植物群落结构的优势种,占物种丰富度的77.27%,硅藻细胞丰度变化范围为0.96×103~1.62×103cells/L,LS组和HS组的硅藻细胞丰度比对照组分别增加了53.53%和69.77%;(3)添加硅酸盐显著促进了小环藻(Cyclotella)、小新月菱形藻(Nitzschia closterium f.minutissima)、圆海链藻(Thalassiosira rotula)等生长(P<0.05),其中小新月菱形藻的藻细胞丰度增加显著,比对照组增加了181.69%;(4)添加硅酸盐对浮游植物多样性和均匀度无显著影响,但可显著增加浮游植物群落结构的物种丰富度(P<0.05)。本结果将为后续探索养殖水域关键时段硅元素补充策略、研发浮游植物初级生产力提升技术进而提高贝类养殖容量的可能性提供基础数据和有价值的线索。

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 about3 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 SiO_(3)-Si(control group);(2) low concentration group:20.00 μmol/L SiO_(3)-Si(group LS);(3) high concentration group:100.00 μmol/L SiO_(3)-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,9species 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 ×103cells/L to 1.62 ×10^(3)cells/L.There was higher abundance of diatom cells in the HS group at the 7th d,with a mean value of 1.62 ×103cells/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 by181.69% 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.