长山群岛海域真核微藻粒级结构及扇贝摄食选择性

采用高通量测序-分子鉴定分级技术于2019年对长山群岛全海域真核微藻粒级结构进行了研究。结果发现，春季以中（47%）、小粒级（41%）为主，夏季以小（39%）、大粒级（38%）为主，秋季以大粒级（60%）为主，春、夏、秋季小、中、大粒级微藻比例为42：47：11、39：23：38、22：18：60。小粒级微藻优势种为细小微胞藻（Micromonas pusilla）、融合微胞藻（Micromonas commoda）和金牛微球藻（Ostreococcus tauri），中粒级微藻优势种为剧毒卡尔藻（Karlodinium veneficum）、大粒级微藻优势种为柔弱几内亚藻（Guinardia delicatula）、平野亚历山大藻（Alexandrium hiranoi）、多纹膝沟藻（Gonyaulax polygramma），综合整个真核微藻群落，春季由中粒径的剧毒卡尔藻占据优势（23.9%），夏季由大粒径的平野亚历山大藻占据优势（29.4%），秋季由大粒径的多纹膝沟藻占据优势（66.8%），有毒甲藻在该海域中占有绝对优势，贝毒累积风险较高，小粒径微藻中金牛微球藻和抑食金球藻曾在渤海引发褐潮，潜在威胁该海域贝类养殖业。虾夷扇贝对小粒级和大粒级微藻的选择性较低，对中粒级微藻的选择性较高，尤其对水体中优势种剧毒卡尔藻一直表现出主动选择。光学需氧量、无机氮、溶解氧、石油类及部分重金属Cd、As、Hg影响着整个长山群岛海域真核微藻粒级结构时空演变。

Particle size structure of eukaryotic microalgae and feeding selectivity of scallops in the waters of Changshan Islands

The Chang-shan Archipelago is the largest island group in the northern waters of the Yellow Sea. It significantly contributes to local economic development due to its abundant aquatic products. In recent years, economically important shellfish (scallops, oysters, and clams) have exhibited growth retardation, thinning, and increased mortality, which has affected the sustainable and healthy development of fisheries. Marine microalgae are the dominant food source for filter-feeding shellfish; they differ in size, physiological functions, and sedimentation rates, which greatly influence the regional ecosystem food web.The microalgae size-fractions are closely related to the nutrient reserves and healthy growth of filter-feeding shellfish.High-throughput sequencing technology can reveal highly diverse eukaryotic lineages, while significantly reducing the errors associated with species identification, particularly microalgae. Importantly, the microalgae composition can be ascertained at multiple taxonomic levels, including at the species level. However, some questions still remain regarding their quantitative estimates. As the number of rDNA copies varies widely among different eukaryotes, it is difficult to determine the abundance of eukaryotic microalgae from rDNA CN-based inferences in environmental samples. However, related studies have demonstrated a significant positive correlation between rDNA sequence polymorphisms and rDNA copy numbersrate. When the size of the cell varies in a population, the rRNA/rDNA quantity reflects the biomass of that population. In this study, the proportion of rDNA copy numbers of eukaryotic microalgae was used to characterize their size distribution (the proportion of pico-, nano-, and microphytoplankton).In aquatic ecosystems, the factors controlling phytoplankton production and their seasonal successions are the main items of phytoplankton ecology. Several factors are linked to the growth and size-fraction structure of phytoplankton, such as the availability of light, temperature, nutrients, competition, and parasitism.Therefore, phytoplankton structure can be considered an integrator of environmental factors.In this study, we used the high-throughput sequencing method to assess the size-fraction structure of phytoplankton as well as the controlling environmental factors around the Changshan Islands. It showed that the proportion of pico-, nano-, and microphytoplankton was 42:47:39 in spring, 39:23:38 in summer, and 22:18:60 in autumn.Micromonas pusilla, Micromonas commoda, and Ostreococcus tauri were the dominant picophytoplankton; Karlodinium veneficum was the dominant nanophytoplankton; and Guinardia delicatula, Alexandrium hiranoi, and Gonyaulax polygramma were the dominant microphytoplankton around the Changshan Archipelago. Moreover, Karlodinium veneficum, Alexandrium hiranoi, and Gonyaulax polygramma were the dominant species in spring, summer, and autumn, respectively. The Mizuhopecten yessoensis selectivity to small and large microalgae was low, while the selectivity to medium microalgae was high, especially to Karlodinium veneficum, the dominant species in water. Environmental factors such as COD(chemical oxygen demand), DIN(dissolved inorganic nitrogen), DO(dissolved oxygen), Oil, Cd, As, and Hg were significantly related to the growth and size-fraction structure of phytoplankton. In the three seasons, Cd and COD were significantly related to the growth of picophytoplankton biomass; DO, DIN, and Oil were significantly related to the growth of picophytoplankton biomass; and COD, As, and Hg were significantly related to the growth of picophytoplankton biomass.