Data_Sheet_1_Saturation Approach to Determine Grazing Mortality in Picoeukaryote and Synechococcus Populations.csv

A substantial component of phytoplankton production in the oceans is channeled through protistan grazers but understanding what dictates the magnitude of this process on a regional and temporal basis is limited, in part, by a shortage of experimental options. A novel saturation approach based on the functional response of planktonic grazers to increasing prey abundance was developed using laboratory cultures of the predator-prey combination of Ochromonas danica and Micromonas pusilla and tested in the coastal waters of the Gulf of Maine. In incubation series, 2 μm polystyrene microspheres were used as surrogate prey to generate increasing levels of saturation of predator ingestion rates of natural prey, resulting in increased rates of apparent growth of the picophytoplankton populations. The relationship between level of addition of surrogate prey to apparent growth, consistently provided significant estimates of maximal growth in the absence of grazing and grazing mortality for populations of picoeukaryotes and Synechococcus. Estimates of gross growth and grazing mortality were comparable to results from dilution experiments carried out in the same waters. The saturation approach represents an additional tool to investigate predator-prey interactions in planktonic communities. Further investigations may show that it can be used to quantify group-specific grazing mortality and growth rates beyond coastal waters and in multiple size classes of prey.

海洋浮游植物生产的重要组成部分是通过原生生物食草动物进行分配，然而，由于实验选项的匮乏，对这一过程在区域和时序尺度上的决定因素的理解受到限制。本研究开发了一种基于浮游食草动物对增多的猎物丰度的功能响应的新型饱和度方法，通过在丹麦念珠藻（Ochromonas danica）和微小拟球藻（Micromonas pusilla）的捕食者-猎物组合的实验室培养中应用，并在缅因湾的近海水中进行测试。在培养系列实验中，以2 μm的聚苯乙烯微球作为替代猎物，以生成不断增加的捕食者摄食自然猎物的饱和度水平，从而提高了原核浮游植物群体的表观生长速率。替代猎物添加水平与表观生长之间的关联，一致地提供了在无食草和食草死亡率条件下，微小真核生物和蓝藻群体的最大生长率的显著估计。总生长率和食草死亡率的估计与在同一水域进行的稀释实验结果相当。饱和度方法为研究浮游群落中的捕食者-猎物相互作用提供了一种额外的工具。进一步的调查可能表明，它可以用于量化特定群体在近海以外的海域以及多种猎物大小类别的食草死亡率和生长速率。