We investigated standing stocks and grazing rates of mesozooplankton assemblages in the Costa Rica Dome (CRD), an open-ocean upwelling ecosystem in the eastern tropical Pacific. While phytoplankton biomass in the CRD is dominated by picophytoplankton (<2-µm cells) with especially high concentrations of Synechococcus spp., we found high mesozooplankton biomass (∼5 g dry weight m-2) and grazing impact (12-50% integrated water column chlorophyll a), indicative of efficient food web transfer from primary producers to higher levels. In contrast to the relative uniformity in water-column chlorophyll a and mesozooplankton biomass, variability in herbivory was substantial, with lower rates in the central dome region and higher rates in areas offset from the dome center. While grazing rates were unrelated to total phytoplankton, correlations with cyanobacteria (negative) and biogenic SiO2 production (positive) suggest that partitioning of primary production among phytoplankton sizes contributes to the variability observed in mesozooplankton metrics. We propose that advection of upwelled waters away from the dome center is accompanied by changes in mesozooplankton composition and grazing rates, reflecting small changes within the primary producers. Small changes within the phytoplankton community resulting in large changes in the mesozooplankton suggest that the variability in lower trophic level dynamics was effectively amplified through the food web.

中文翻译：

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哥斯达黎加圆顶的中浮游生物生物量和放牧：通过浮游生物食物网放大变异性

我们调查了哥斯达黎加圆顶 (CRD) 中中型浮游生物组合的常备种群和放牧率，这是热带太平洋东部的一个公海上升流生态系统。虽然 CRD 中的浮游植物生物量以具有特别高浓度的聚球藻属的微型浮游植物（<2-µm 细胞）为主，但我们发现中型浮游生物生物量（~5 g 干重 m-2）和放牧影响（12-50% 综合水柱叶绿素 a)，表明食物网从初级生产者有效转移到更高水平。与水柱叶绿素 a 和中型浮游生物生物量的相对均匀性相反，食草动物的变异性很大，中央圆顶区域的比率较低，而偏离圆顶中心的区域的比率较高。虽然放牧率与浮游植物总量无关，与蓝藻（负）和生物 SiO2 产量（正）的相关性表明，初级生产在浮游植物大小之间的分配有助于在中型浮游生物指标中观察到的变异性。我们建议远离圆顶中心的上涌水的平流伴随着中型浮游生物组成和放牧率的变化，反映了初级生产者内部的微小变化。浮游植物群落内的微小变化导致中型浮游动物的巨大变化表明低营养级动态的变异性通过食物网被有效放大。我们建议远离圆顶中心的上涌水的平流伴随着中型浮游生物组成和放牧率的变化，反映了初级生产者内部的微小变化。浮游植物群落内的微小变化导致中型浮游动物的巨大变化表明低营养级动态的变异性通过食物网被有效放大。我们建议远离圆顶中心的上涌水的平流伴随着中型浮游生物组成和放牧率的变化，反映了初级生产者内部的微小变化。浮游植物群落内的微小变化导致中型浮游动物的巨大变化表明低营养级动态的变异性通过食物网被有效放大。