Anthropogenic and/or climate-driven changes in zooplankton dynamics may serve as a bottom-up regulator of productivity of small pelagic fish. In the central Seto Inland Sea of Japan, the abundance of the recruit fish of Japanese anchovy (Engraulis japonicus) has markedly declined in the last decade under oligotrophication. However, the link between the reproductive success of anchovy and environmental variation is largely unclear. This study explored the potential association between changes in the zooplankton (copepods) community structure and the reproductive condition of anchovy in this oligotrophic sea using survey data from spring to summer of 2001–2019. The community structure of copepod species changed markedly in May–July, covering the main spawning season of anchovy, as decreases in the biomass of several copepods found in cooler water in a given season (May–June) were observed. Although relationships between chlorophyll a concentrations and the copepod biomass were unclear, the recent decline of their cooler-water copepods may be attributed to the influences of elevated sea surface temperature and decreasing levels of chlorophyll a. The latter may be associated with decreasing nitrogen levels. Among these species, Calanus sinicus and Corycaeus affinis could be important prey items for anchovy from the analyses of prey selectivity and relationships between the relative condition factor of females and the copepod biomass. The egg size–temperature relationships of anchovy appeared to be associated with the relative condition factor of females and survival rates in the early stage of life, suggesting that females with a poor body condition produced smaller eggs in recent years. Maternal food manipulation experiments supported the assumption that larvae born to females fed a restricted food ration exhibited lower starvation tolerance and slower growth than born to females provided feed ad libitum. These findings suggest that the reproductive success of anchovy could be subject to bottom-up trophic drivers mediated by maternal contributions to offspring viability, and this partly explains why the level of anchovy recruitment has rapidly declined in the last decade.

浮游动物动力学的人为和/或气候驱动的变化可以作为小型中上层鱼类生产力的自下而上调节器。在日本濑户内海中部，盛产日本鳀鱼（Engraulis japonicus) 在过去十年中在贫营养化的情况下显着下降。然而，鳀鱼的繁殖成功与环境变异之间的联系在很大程度上尚不清楚。本研究利用 2001 年至 2019 年春季至夏季的调查数据，探讨了浮游动物（桡足类）群落结构变化与鳀鱼在贫营养海洋中繁殖状况之间的潜在关联。桡足类物种的群落结构在 5 月至 7 月期间发生了显着变化，涵盖了鳀鱼的主要产卵季节，因为观察到在特定季节（5 月至 6 月）在较冷水中发现的几种桡足类的生物量减少。虽然叶绿素a之间的关系浓度和桡足类生物量尚不清楚，但其较冷水桡足类最近的下降可能归因于海面温度升高和叶绿素a水平下降的影响。后者可能与氮水平降低有关。在这些物种中，Calanus sinicus和Corycaeus affinis从猎物选择性和雌性相对条件因素与桡足类生物量之间的关系分析，可能是鳀鱼的重要猎物。鳀鱼卵的大小-温度关系似乎与雌性的相对条件因素和生命早期的存活率有关，这表明近年来身体状况不佳的雌性产卵较小。母体食物操作实验支持这样的假设，即喂食有限食物配给的雌性所生的幼虫比提供任意饲料的雌性所生的幼虫表现出更低的饥饿耐受性和更慢的生长。. 这些研究结果表明，鳀鱼的繁殖成功可能受到母体对后代生存能力的贡献所介导的自下而上的营养驱动因素，这部分解释了为什么在过去十年中鳀鱼招募水平迅速下降。