Data_Sheet_3_Freshwater Microbial Eukaryotic Core Communities, Open-Water and Under-Ice Specialists in Southern Victoria Island Lakes (Ekaluktutiak, NU, Canada).PDF

Across much of the Arctic, lakes and ponds dominate the landscape. Starting in late September, the lakes are covered in ice, with ice persisting well into June or early July. In summer, the lakes are highly productive, supporting waterfowl and fish populations. However, little is known about the diversity and ecology of microscopic life in the lakes that influence biogeochemical cycles and contribute to ecosystem services. Even less is known about the prevalence of species that are characteristic of the seasons or whether some species persist year-round under both ice cover and summer open-water conditions. To begin to address these knowledge gaps, we sampled 10 morphometrically diverse lakes in the region of Ekaluktutiak (Cambridge Bay), on southern Victoria Island (NU, Canada). We focused on Greiner Lake, the lakes connected to it, isolated ponds, and two nearby larger lakes outside the Greiner watershed. The largest lakes sampled were Tahiryuaq (Ferguson Lake) and the nearby Spawning Lake, which support commercial sea-run Arctic char (Salvelinus alpinus) fisheries. Samples for nucleic acids were collected from the lakes along with limnological metadata. Microbial eukaryotes were identified with high-throughput amplicon sequencing targeting the V4 region of the 18S rRNA gene. Ciliates, dinoflagellates, chrysophytes, and cryptophytes dominated the lake assemblages. A Bray–Curtis dissimilarity matrix separated communities into under-ice and open-water clusters, with additional separation by superficial lake area. In all, 133 operational taxonomic units (OTUs) occurred either in all under-ice or all open-water samples and were considered “core” microbial species or ecotypes. These were further characterized as seasonal indicators. Ten of the OTUs were characteristic of all lakes and all seasons sampled. Eight of these were cryptophytes, suggesting diverse functional capacity within the lineage. The core open-water indicators were mostly chrysophytes, with a few ciliates and uncharacterized Cercozoa, suggesting that summer communities are mixotrophic with contributions by heterotrophic taxa. The core under-ice indicators included a dozen ciliates along with chrysophytes, cryptomonads, and dinoflagellates, indicating a more heterotrophic community augmented by mixotrophic taxa in winter.

在北极大部分区域，湖泊与池塘构成了地表景观的主体。自9月下旬起，湖泊便被冰层覆盖，冰盖可一直留存至次年6月乃至7月初。夏季时，这些湖泊生产力旺盛，支撑了水鸟与鱼类种群的繁衍。然而，人们对湖泊中驱动生物地球化学循环、支撑生态系统服务的微型生物的多样性与生态学特征却知之甚少。而对于季节特有物种的分布与丰度情况，以及是否有部分物种能在冰盖覆盖与夏季敞水两种环境下全年存续，我们的认知则更为匮乏。

为填补这些认知空白，我们在加拿大努纳武特地区维多利亚岛南部的埃卡卢克图蒂亚克（剑桥湾）区域，对10座形态特征各异的湖泊开展了系统采样。本次采样聚焦格雷纳湖及其连通湖泊、孤立池塘，以及格雷纳流域外围附近的两座大型湖泊。本次采样覆盖的最大两座湖泊为塔希里约阿克（弗格森湖）与邻近的产卵湖，二者均支撑商业化洄游北极红点鲑（*Salvelinus alpinus*）渔业。我们同步采集了各湖泊的核酸样本与湖沼学元数据（limnological metadata）。研究采用针对18S rRNA基因（18S rRNA gene）V4区的高通量扩增子测序（high-throughput amplicon sequencing）技术，对微型真核生物（microbial eukaryotes）进行了物种鉴定。

纤毛虫（Ciliates）、甲藻（dinoflagellates）、金藻（chrysophytes）与隐藻（cryptophytes）构成了湖泊群落的优势类群。基于布赖斯-柯蒂斯相异矩阵（Bray–Curtis dissimilarity matrix）的分析将群落划分为冰下与敞水两个类群，同时湖泊表面积也会带来额外的群落分异。总计有133个操作分类单元（operational taxonomic units, OTUs）仅在全部冰下样本或全部敞水样本中被检出，被归为"核心"微生物类群或生态型（ecotypes）。这些类群可进一步被划分为季节指示类群。其中10个OTUs为所有采样湖泊与所有采样季节所共有，其中8个为隐藻，这表明该演化支内存在多样的功能潜能。

核心敞水指示类群以金藻为主，同时包含少量纤毛虫与未分类的丝足虫类（Cercozoa），这表明夏季群落兼具混合营养型（mixotrophic）与异养类群（heterotrophic taxa）的贡献。核心冰下指示类群包含十余种纤毛虫，以及金藻、隐滴虫与甲藻，这表明冬季群落以异养为主，混合营养类群为其提供了补充。