Pelagic zooplankton samples from Lake Biwa, Japan, collected monthly since 1971, were analyzed for biomass and body size structure. Our aim was to clarify the relative effects of food availability and global warming vs. top‐down control by fish predation on long‐term trends. Annual mean biomass and density‐weighted body size were calculated and compared with water temperature, total phosphorus (TP), as a proxy of food amount, and catch per unit effort (CPUE) of Ayu (Plecoglossus altivelis altivelis), as a proxy of planktivorous fish predation pressure. Mean water temperature above 20 m increased by 0.94°C. TP increased until 1974 and then decreased until 1985, becoming stable after that. Ayu CPUE increased until 1987 and then declined. The study period can be divided into two nutritional phases: a high TP phase (1971–1985) and a low‐stable TP phase (1986–2010). Five zooplankton taxa, Eodiaptomus japonicus, Cyclopoida spp., Daphnia spp., Bosmina longirostris, and Diaphanosoma orientalis, were continuously dominant. Annual mean total crustacean biomass varied from 0.3 to 3.6 g dry weight m⁻², slightly decreasing until 1993 but increasing thereafter. Generalized linear models showed that annual mean body sizes were affected by temperature and CPUE, whereas annual mean biomass was affected by TP and CPUE. These had no effect during the high TP phase, whereas only CPUE affected both traits during the low‐stable TP phase. We concluded that zooplankton biomass and body size long‐term trends were mostly influenced by fish predation and that eutrophication and global warming impacts might be affected by top‐down control.

中文翻译：

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鳞翅目鱼类的捕食掩盖了日本琵琶湖浮游动物生物量和体型结构的十年趋势的人为干扰

自1971年以来每月采集来自日本琵琶湖的浮游浮游动物样本，分析其生物量和体型结构。我们的目的是弄清粮食供应和全球变暖与鱼类捕食对自上而下的控制对长期趋势的相对影响。计算了年平均生物量和密度加权的体重，并将其与水温，总磷（TP）进行比较，以作为食物量的代名词，并与Ayu（Plecoglossus altivelis altivelis）的单位努力量（CPUE）进行比较。），作为浮游鱼类捕食压力的代表。20 m以上的平均水温升高0.94°C。TP直到1974年才增加，然后一直下降到1985年，此后趋于稳定。Ayu CPUE一直增长到1987年，然后下降。研究阶段可分为两个营养阶段：高TP阶段（1971-1985）和低稳定TP阶段（1986-2010）。五个浮游动物类群，日本大叶虾（Eodiaptomus japonicus），环足类（Cyclopoida spp。），水蚤（Daphnia spp。），长白菜（Bosmina longirostris）和侧柏（Diaphanosoma Orientalis）一直占优势。甲壳类生物年平均总生物量为0.3至3.6 g干重m ^-2，直到1993年略有下降，但此后有所增加。广义线性模型表明，年平均体形受温度和CPUE的影响，而年平均生物量受TP和CPUE的影响。这些在高TP阶段没有影响，而只有CPUE在低稳定TP阶段影响了这两个性状。我们得出的结论是，浮游生物的生物量和体重的长期趋势主要受鱼类捕食的影响，而富营养化和全球变暖的影响可能受自上而下控制的影响。