Meunier Cédric L, Liess Antonia, Andersson Agneta, Brugel Sonia, Paczkowska Joanna, Rahman Habib, Skoglund Bjorn, Rowe Owen F
Department of Ecology and Environmental Sciences, Umeå University, 901 87 Umeå, Sweden.
Department of Ecology and Environmental Sciences, Umeå University, 901 87 Umeå, Sweden; Rydberg Laboratory of Applied Science, School of Business, Science and Engineering, Halmstad University, Halmstad, Sweden.
Mar Environ Res. 2017 Aug;129:236-244. doi: 10.1016/j.marenvres.2017.06.008. Epub 2017 Jun 15.
Climate change predictions indicate that coastal and estuarine environments will receive increased terrestrial runoff via increased river discharge. This discharge transports allochthonous material, containing bioavailable nutrients and light attenuating matter. Since light and nutrients are important drivers of basal production, their relative and absolute availability have important consequences for the base of the aquatic food web, with potential ramifications for higher trophic levels. Here, we investigated the effects of shifts in terrestrial organic matter and light availability on basal producers and their grazers. In twelve Baltic Sea mesocosms, we simulated the effects of increased river runoff alone and in combination. We manipulated light (clear/shade) and carbon (added/not added) in a fully factorial design, with three replicates. We assessed microzooplankton grazing preferences in each treatment to assess whether increased terrestrial organic matter input would: (1) decrease the phytoplankton to bacterial biomass ratio, (2) shift microzooplankton diet from phytoplankton to bacteria, and (3) affect microzooplankton biomass. We found that carbon addition, but not reduced light levels per se resulted in lower phytoplankton to bacteria biomass ratios. Microzooplankton generally showed a strong feeding preference for phytoplankton over bacteria, but, in carbon-amended mesocosms which favored bacteria, microzooplankton shifted their diet towards bacteria. Furthermore, low total prey availability corresponded with low microzooplankton biomass and the highest bacteria/phytoplankton ratio. Overall our results suggest that in shallow coastal waters, modified with allochthonous matter from river discharge, light attenuation may be inconsequential for the basal producer balance, whereas increased allochthonous carbon, especially if readily bioavailable, favors bacteria over phytoplankton. We conclude that climate change induced shifts at the base of the food web may alter energy mobilization to and the biomass of microzooplankton grazers.
气候变化预测表明，沿海和河口环境将因河流流量增加而接收更多的陆地径流。这种径流输送着外来物质，其中包含生物可利用的养分和光衰减物质。由于光和养分是基础生产的重要驱动因素，它们的相对和绝对可利用性对水生食物网的基础具有重要影响，并可能对更高营养级产生潜在影响。在此，我们研究了陆地有机物质和光可利用性的变化对基础生产者及其捕食者的影响。在12个波罗的海中型生态系统中，我们单独模拟了河流径流增加的影响以及两者共同作用的影响。我们采用完全析因设计，通过控制光（清澈/阴暗）和碳（添加/不添加），设置了三个重复。我们评估了每种处理中微型浮游动物的摄食偏好，以确定陆地有机物质输入增加是否会：（1）降低浮游植物与细菌的生物量比；（2）使微型浮游动物的食物来源从浮游植物转向细菌；（3）影响微型浮游动物的生物量。我们发现，添加碳会导致浮游植物与细菌的生物量比降低，但降低光照水平本身并不会产生这种效果。微型浮游动物通常对浮游植物的摄食偏好远高于细菌，但是，在有利于细菌生长的添加碳的中型生态系统中，微型浮游动物的食物来源转向了细菌。此外，猎物的总可利用性较低与微型浮游动物生物量较低以及细菌/浮游植物比最高相对应。总体而言，我们的结果表明，在因河流排放的外来物质而改变的浅海沿岸水域中，光衰减对基础生产者的平衡可能影响不大，而增加的外来碳，特别是如果易于生物利用，会使细菌比浮游植物更占优势。我们得出结论，气候变化引起的食物网基础变化可能会改变向微型浮游动物捕食者的能量流动以及它们的生物量。
