Data_Sheet_3_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动物食草者进行转化，然而，由于实验选项的匮乏，理解这一过程在区域和时空尺度上的决定因素受到了限制。基于浮游食草者对增加的猎物丰度的功能响应，一种新的饱和度方法被开发出来，并利用丹氏裸藻与微型裸藻的捕食者-猎物组合在实验室中进行培养，并在缅因湾的近海区域进行测试。在孵化系列实验中，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，从而引发小型浮游植物种群显著生长率的提升。替代猎物添加水平与显著生长率之间的关系，为无食草和食草死亡率下微核糖体生物和蓝藻种群的最大生长提供了显著估计。总生长率和食草死亡率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额外的工具。进一步的调查可能会显示，它可以用以量化特定群体在海岸水域之外的食草死亡率和生长率，以及猎物多种大小类别的生长。