Data_Sheet_2_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巨大部分是通过原生生物食草动物进行的，然而，由于实验选项的匮乏，理解这一过程在区域和时间尺度上的决定因素受到了限制。本研究开发了一种基于浮游食草动物对增加的猎物丰度的功能反应的新型饱和度方法。该方法利用丹麦念珠藻（Ochromonas danica）和微小拟微藻（Micromonas pusilla）的捕食者-猎物组合的实验室培养物进行测试，并在缅因湾的沿海水域进行实验。在孵化系列中，使用2微米的聚苯乙烯微球作为替代猎物，以生成不断增高的捕食者对自然猎物的摄入率饱和度，从而增加了极小浮游植物种群的实际生长速率。替代猎物添加水平与实际生长之间的关系，为微小真核生物和蓝藻种群在没有捕食和捕食死亡率情况下的最大生长提供了显著的估计值。总生长率和捕食死亡率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生物群落中的捕食者-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沿海水域以外的捕食死亡率和生长速率，以及在不同大小的猎物种群中。