Food quality is one of the key factors influencing zooplankton population dynamics. Eutrophication drives phytoplankton communities toward the dominance of cyanobacteria, which means a decrease in the availability of sterols and long-chain polyunsaturated fatty acids (EPA and DHA). The effects of different restoration measures on the nutritional quality of the phytoplankton community and subsequent impacts on zooplankton biomass have rarely been considered. We analyzed the nutritional quality of phytoplankton in the eutrophic Lake Vesijarvi in southern Finland over a 37-year period, and studied the impacts of two restoration measures, biomanipulation and hypolimnetic aeration, on the abundance of high-quality phytoplankton. We found that biomanipulation had a positive impact on the abundance of taxa synthesizing sterols, EPA, and DHA and, concurrently, on the biomass of the keystone species Daphnia. In contrast, hypolimnetic aeration did not result in such a beneficial outcome, manifested as a decrease in the abundance of Daphnia and frequent phytoplankton blooms dominated by cyanobacteria suggesting reduction in the nutritional quality of food for Daphnia. Our analysis shows that the determination of the nutritional value of algae and the contribution of essential fatty acids and sterols is an effective method to evaluate the success of various restoration measures.

中文翻译：

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湖泊恢复影响藻类的营养质量，从而影响水蚤的生物量

食品质量是影响浮游动物种群动态的关键因素之一。富营养化促使浮游植物群落以蓝藻为主，这意味着甾醇和长链多不饱和脂肪酸（EPA 和 DHA）的可用性降低。很少考虑不同恢复措施对浮游植物群落营养质量的影响以及随后对浮游动物生物量的影响。我们分析了 37 年来芬兰南部富营养化的 Vesijarvi 湖中浮游植物的营养质量，并研究了两种恢复措施，即生物操纵和低温曝气对优质浮游植物丰度的影响。我们发现生物操纵对合成甾醇、EPA 和 DHA 的类群的丰度有积极影响，同时，关于关键物种水蚤的生物量。相比之下，低温曝气并没有产生如此有益的结果，表现为水蚤丰度的减少和以蓝藻为主的浮游植物频繁大量繁殖，这表明水蚤食物的营养质量下降。我们的分析表明，确定藻类的营养价值和必需脂肪酸和甾醇的贡献是评估各种恢复措施成功与否的有效方法。