Mechanistic understanding of the role of diatoms in the success of the Arctic Calanus complex and implications for a warmer Arctic

哲水蚤属（Calanus）的桡足类物种是米粒大小的甲壳类动物，是螃蟹和龙虾的远亲，遍布北冰洋，消耗大量的微型藻类（浮游植物）。这些微小的动物是许多北极鱼类、海鸟和鲸鱼的主要食物来源。早春时节，它们饱餐季节性大量繁殖的硅藻，这是一种富含脂肪的浮游植物，在海冰下和开阔的海洋中繁殖。这使得哲水蚤能够迅速获得足够的脂肪，以在北极冬季数月的食物短缺中生存下来。硅藻还产生一种主要的海洋ω-3多不饱和脂肪酸，哲水蚤需要这种脂肪酸才能在冰冻的北极沃茨中成功生存和繁殖。哲水蚤季节性地迁移到更深的沃茨，以节省能量，并减少在越冬过程中被捕食的损失，这一过程被称为滞育，完全由富含碳的脂肪（脂质）提供燃料。这种垂直的“脂质泵”将大量的碳转移到海洋内部，最终代表了大气二氧化碳（CO2）的下降，这是全球碳循环中的一个重要过程。预计整个世纪持续的全球变暖将对北冰洋硅藻生产力的时间、规模和空间分布产生强烈影响。人们对哲水蚤如何应对这些变化知之甚少，因此很难理解更广泛的北极生态系统及其生物地球化学将如何受到气候变化的影响。该提案的总体目标是对未来气候变化将如何影响北极的哲水蚤进行预测性了解。我们将通过五个主要研究领域来实现这一目标：我们将综合过去北极哲水蚤的数据集，以及来自卫星的初级生产数据。这项工作将研究更小，更温和的物种是否越来越多地在北极殖民。此外，它将考虑生命周期事件的时间在过去几十年中以及在不同北极地区之间可能发生的变化。由此产生的数据将用于验证建模工作。我们将进行实地实验，以研究气候驱动的浮游植物数量和omega-3含量的变化如何影响哲水蚤生命周期的关键特征，包括繁殖和滞育的脂质储存。尖端技术将调查如何以及为什么哲水蚤使用储存的脂肪在没有食物的情况下繁殖。所获得的新认识将用于制作哲水蚤生命周期的数值模型，以供未来预测，该研究方案将开发哲水蚤生命周期模型，并模拟北极大片地区目前的分布模式、生命周期事件的时间和储存的脂质量（身体状况）。这些预测将与历史数据进行比较。我们将调查哲水蚤的ω-3脂肪酸含量如何受到食物环境的影响，从而决定它们的滞育模式-以及繁殖成功。不同种类的哲水蚤的繁殖策略不同，这种方法提供了一种强大的手段来预测每个物种将如何受到影响，使我们能够在未来环境变化的各种情况下确定赢家和输家。该项目综合报告将借鉴先前提案的所有要素，以生成新的哲水蚤数值模型，以及食物环境如何影响它们的生殖策略，从而影响它们在不断变化的北冰洋中的生存能力。这将使我们能够探索北冰洋的生产力和地球化学在未来将如何变化。这些模型将与联合王国的地球系统模型接口，直接为国际努力提供信息，以了解全球对气候变化的反馈。

Copepod species of the genus Calanus (Calanus hereafter) are rice grain-sized crustaceans, distant relatives of crabs and lobsters, that occur throughout the Arctic Ocean consuming enormous quantities of microscopic algae (phytoplankton). These tiny animals represent the primary food source for many Arctic fish, seabirds and whales. During early spring they gorge on extensive seasonal blooms of diatoms, fat-rich phytoplankton that proliferate both beneath the sea ice and in the open ocean. This allows Calanus to rapidly obtain sufficient fat to survive during the many months of food scarcity during the Arctic winter. Diatoms also produce one of the main marine omega-3 polyunsaturated fatty acids that Calanus require to successfully survive and reproduce in the frozen Arctic waters. Calanus seasonally migrate into deeper waters to save energy and reduce their losses to predation in an overwintering process called diapause that is fuelled entirely by carbon-rich fat (lipids). This vertical 'lipid pump' transfers vast quantities of carbon into the ocean's interior and ultimately represents the draw-down of atmospheric carbon dioxide (CO2), an important process within the global carbon cycle. Continued global warming throughout the 21st century is expected to exert a strong influence on the timing, magnitude and spatial distribution of diatom productivity in the Arctic Ocean. Little is known about how Calanus will respond to these changes, making it difficult to understand how the wider Arctic ecosystem and its biogeochemistry will be affected by climate change. The overarching goal of this proposal is to develop a predictive understanding of how Calanus in the Arctic will be affected by future climate change. We will achieve this goal through five main areas of research:We will synthesise past datasets of Calanus in the Arctic alongside satellite-derived data on primary production. This undertaking will examine whether smaller, more temperate species have been increasingly colonising of Arctic. Furthermore, it will consider how the timing of life-cycle events may have changed over past decades and between different Arctic regions. The resulting data will be used to validate modelling efforts.We will conduct field based experiments to examine how climate-driven changes in the quantity and omega-3 content of phytoplankton will affect crucial features of the Calanus life-cycle, including reproduction and lipid storage for diapause. Cutting-edge techniques will investigate how and why Calanus use stored fats to reproduce in the absence of food. The new understanding gained will be used to produce numerical models of Calanus' life cycle for future forecasting.The research programme will develop life-cycle models of Calanus and simulate present day distribution patterns, the timing of life-cycle events, and the quantities of stored lipid (body condition), over large areas of the Arctic. These projections will be compared to historical data.We will investigate how the omega-3 fatty acid content of Calanus is affected by the food environment and in turn dictates patterns of their diapause- and reproductive success. Reproductive strategies differ between the different species of Calanus and this approach provides a powerful means by which to predict how each species will be impacted, allowing us to identify the winners and losers under various scenarios of future environmental changes. The project synthesis will draw upon previous all elements of the proposal to generate new numerical models of Calanus and how the food environment influences their reproductive strategy and hence capacity for survival in a changing Arctic Ocean. This will allow us to explore how the productivity and biogeochemistry of the Arctic Ocean will change in the future. These models will be interfaced with the UK's Earth System Model that directly feeds into international efforts to understand global feedbacks to climate change.