DataSheet_4_Diversity and biogeography of dinoflagellates in the Kuroshio region revealed by 18S rRNA metabarcoding.xlsx

Dinoflagellate is one of the most diverse and pervasive protists and a fundamental player in the marine food web dynamics and biogeochemical cycles. While possessing different nutritional strategies from purely autotrophy or heterotrophy to mixotrophy, some of them are also known as toxic harmful algal bloom (HAB) formers over the world. Despite their ordinariness, their diversity and biogeography are understudied in the open ocean compared with coastal region. As the first metabarcoding survey covering the Kuroshio current region from the offshore of Okinawa to the south of Honshu, we investigated the distribution of free-living dinoflagellates using the hypervariable V4 and V9 regions on 18S rRNA and their relation to ambient environments influenced by this oligotrophic but highly productive current in the northwest Pacific Ocean. We observed community structures differentiated by depth and nutrient concentrations. Most species annotated are autotrophic or mixotrophic and had a distribution correlated to warmer surface water, whereas heterotrophic species correlated to high nutrient levels or deeper layer. Our results also confirmed the overall high genetic diversity of dinoflagellates that decreased with depth and onshore. Most species present at stations offshore, and the relative abundance of HAB assemblages was lower at nutrient-rich stations on the continental shelf than stations influenced by the Kuroshio current, exhibiting the role of the Kuroshio transporting dinoflagellates including HAB species. To fully understand the dynamics of dinoflagellate communities in marine ecosystems, further seasonal monitoring is foremost for correlating dinoflagellates and environmental factors while completing the reference genomic database.

甲藻（Dinoflagellate）是多样性最为丰富、分布最为广泛的原生生物类群之一，在海洋食物网动态与生物地球化学循环中发挥着核心作用。其营养策略多元，涵盖专性自养、专性异养至兼性营养等多种模式，其中部分类群还是全球范围内已知的有毒有害藻华（Harmful Algal Bloom, HAB）成因物种。尽管甲藻分布普遍，但相较于近岸海域，开阔大洋中针对其多样性与生物地理分布的研究仍相对不足。
本研究作为首次覆盖黑潮（Kuroshio Current）流域（从冲绳近海至本州南部）的元条形码（metabarcoding）调查，依托18S rRNA基因的高变V4区与V9区，对西北太平洋这片受寡营养但高生产力海流影响的海域内的自由生活甲藻分布进行了系统探究，并分析其与周边环境因子的关联。
研究结果显示，甲藻群落结构随水深与营养盐浓度呈现显著分化。多数注释获得的物种为自养或兼性营养型，其分布与温暖表层水体呈显著正相关；而异养物种则多与高营养盐环境或深层水体相关联。本研究同时证实了甲藻整体具有较高的遗传多样性，且该多样性随水深增加与向岸推进逐渐降低。大部分物种分布于近海站位，且大陆架富营养站位的有害藻华类群相对丰度显著低于受黑潮影响的站位，这印证了黑潮在输送包括有害藻华物种在内的甲藻过程中所扮演的重要角色。
若要全面理解海洋生态系统中甲藻群落的动态变化，后续需优先开展季节性监测以建立甲藻与环境因子的关联，并完善参考基因组数据库。