Data from: The importance of phytoplankton biomolecule availability for secondary production

The growth and reproduction of animals is affected by their access to resources. In aquatic ecosystems, the availability of essential biomolecules for filter-feeding zooplankton depends greatly on phytoplankton. Here, we analyzed the biochemical composition, i.e., the fatty acid, sterol and amino acid profiles and concentrations as well as protein, carbon, nitrogen, and phosphorus content of 17 phytoplankton monocultures representing the seven most abundant phytoplankton classes in boreal and sub-arctic lakes. To examine how the differences in the biochemical composition between phytoplankton classes affect their nutritional quality for consumers, we assessed the performance of Daphnia, on these diets. Furthermore, we defined the most important biomolecules regulating the somatic growth and reproduction of Daphnia, expecting that higher concentrations of certain biomolecules are needed for reproduction than for growth. Finally, we combined these results with phytoplankton field data from over 900 boreal and sub-arctic lakes in order to estimate whether the somatic growth of Daphnia is sterol-limited when the natural phytoplankton communities are cyanobacteria-dominated. Our analysis shows that Daphnia grows best with phytoplankton rich in sterols, ω-3 fatty acids, protein, and amino acids. Their reproduction follows food sterol and ω-3 concentration as well as C:P-ratio being two times higher in Daphnia feeding on cryptophytes than any other diet. Interestingly, we found that a high dietary ω-6 fatty acid concentration decreases both somatic growth and reproduction of Daphnia. When combined with phytoplankton community composition field data, our results indicate that zooplankton is constantly limited by sterols in lakes dominated by cyanobacteria (≥40% of total phytoplankton biomass), and that the absence of cryptophytes can severely hinder zooplankton production in nature.

动物的生长与繁殖受其可获取的资源状况影响。在水生生态系统中，滤食性浮游动物（filter-feeding zooplankton）所需的关键生物分子的可获得性，在很大程度上依赖于浮游植物（phytoplankton）。本研究针对17株浮游植物单种培养物展开分析，涵盖了北方与亚北极湖泊中7类最优势的浮游植物类群，测定了其生化组成，包括脂肪酸、固醇、氨基酸的谱图与浓度，以及蛋白质、碳、氮、磷的含量。为探究浮游植物类群间生化组成的差异如何影响其作为消费者饵料的营养品质，我们以这些浮游植物为饵料，评估了水蚤（Daphnia）的生长与繁殖表现。此外，我们明确了调控水蚤个体生长与繁殖的关键生物分子，并推测相较于个体生长，水蚤的繁殖过程需要更高浓度的特定生物分子。最后，我们将上述研究结果与取自900余个北方及亚北极湖泊的浮游植物野外调查数据相结合，以此估算当自然浮游植物群落以蓝藻（cyanobacteria）占主导时，水蚤的个体生长是否受到固醇限制。分析结果表明，水蚤在投喂富含固醇、ω-3脂肪酸、蛋白质及氨基酸的浮游植物时，生长表现最佳。水蚤的繁殖情况与饵料中的固醇、ω-3浓度以及碳磷比（C:P-ratio）密切相关；其中以隐藻（cryptophytes）为食的水蚤组，上述指标较其他所有饵料组高出两倍。值得注意的是，我们发现饵料中高浓度的ω-6脂肪酸会同时抑制水蚤的个体生长与繁殖。结合浮游植物群落组成的野外调查数据，我们的研究结果显示：在蓝藻占总浮游植物生物量≥40%的湖泊中，浮游动物始终受到固醇限制；而自然环境中若缺乏隐藻，则会严重抑制浮游动物的种群生产。