Table_2_Protistan Communities Within the Galápagos Archipelago With an Emphasis on Micrograzers.xlsx

The Galápagos Archipelago is a globally significant biodiversity hotspot. However, compared to the relatively well-known megafauna, the distribution and ecological significance of marine protists in this system are poorly understood. To gain an understanding of the protistan assemblages across trophic modes, an intensive oceanographic survey was conducted in the Galápagos Marine Reserve (GMR) in October of 2018. The Equatorial Undercurrent (EUC)-influenced region had higher chlorophyll-a (Chl-a) concentrations than those of the eastern regions of the archipelago, along with higher abundances of protistan grazers. Specifically, proportions of autotrophic and potentially mixotrophic dinoflagellates were higher in the EUC, whereas in the eastern regions, heterotrophic dinoflagellates and chlorophytes dominated. Taxonomic composition and biochemical indicators suggested proportions of micrograzers and their associated heterotrophic biomass was higher in the oligotrophic, low Chl-a regions in the east. We also report observations from a dinoflagellate bloom in the western archipelago, which was heavily influenced by upwelling of the EUC. The red tide-forming dinoflagellate Scrippsiella lachrymosa was highly detected through light microscopy and DNA amplicon sequencing. In addition, the heterotrophic dinoflagellate Polykrikos kofoidii was detected and, based on cell densities observed in this study and grazing rates obtained from the literature, estimated to potentially graze up to 62% of S. lachrymosa bloom population. Our findings thus provide new insights into the composition of micrograzers and their potential roles in structuring protistan communities in the Galápagos Archipelago.

加拉帕戈斯群岛（Galápagos Archipelago）是全球重要的生物多样性热点区域。然而，相较于知名度较高的大型动物群（megafauna），该海域海洋原生生物（marine protists）的分布特征与生态意义却鲜为人知。为明确不同营养模式（trophic modes）下的原生生物群落组成，研究团队于2018年10月在加拉帕戈斯海洋保护区（Galápagos Marine Reserve, GMR）开展了密集的海洋学调查。受赤道潜流（Equatorial Undercurrent, EUC）影响的海域，其叶绿素a（chlorophyll-a, Chl-a）浓度高于群岛东部海域，同时原生生物捕食者（protistan grazers）的丰度也更高。具体而言，赤道潜流影响区的自养型（autotrophic）与潜在混合营养型（mixotrophic）甲藻（dinoflagellates）占比更高，而东部海域则以异养型（heterotrophic）甲藻和绿藻（chlorophytes）占主导。分类组成（taxonomic composition）与生化指标（biochemical indicators）显示，东部寡营养（oligotrophic）、低叶绿素a海域的微型捕食者（micrograzers）及其相关异养生物量（heterotrophic biomass）占比更高。本研究还记录了群岛西部海域的一次甲藻水华（dinoflagellate bloom）事件，该水华受赤道潜流上升流（upwelling）的强烈影响。研究通过光学显微镜与DNA扩增子测序（DNA amplicon sequencing）技术，均检测到了引发赤潮（red tide）的甲藻物种泪面斯氏藻（Scrippsiella lachrymosa）。此外，研究还检测到异养型甲藻科氏多肢甲藻（Polykrikos kofoidii）；结合本研究观测的细胞密度与文献报道的捕食速率，估算该物种可捕食多达62%的泪面斯氏藻水华种群。综上，本研究的发现为明确加拉帕戈斯群岛微型捕食者的群落组成，及其在塑造原生生物群落结构中的潜在作用提供了新的科学认知。