Morison Francoise, Pierson James Joseph, Oikonomou Andreas, Menden-Deuer Susanne
Graduate School of Oceanography, University of Rhode Island, Narragansett, RI, United States of America.
Center for Environmental Science, University of Maryland, Cambridge, MD, USA.
PeerJ. 2020 Jul 17;8:e9430. doi: 10.7717/peerj.9430. eCollection 2020.
The impacts of grazing by meso- and microzooplankton on phytoplankton primary production (PP) was investigated in the surface layer of the western North Atlantic during spring. Shipboard experiments were performed on a latitudinal transect at three stations that differed in mixed layer depth, temperature, and mesozooplankton taxonomic composition. The mesozooplankton community was numerically dominated by at the northern and central station, with also present at the northern station. The southern station was >10 °C warmer than the other stations and had the most diverse mesozooplankton assemblage, dominated by small copepods including spp. Microzooplankton grazing was detected only at the northern station, where it removed 97% of PP. Estimated clearance rates by and suggested that at in-situ abundance these mesozooplankton were not likely to have a major impact on phytoplankton abundance, unless locally aggregated. Although mesozooplankton grazing impact on total phytoplankton was minimal, these grazers completely removed the numerically scarce > 10 µm particles, altering the particle-size spectrum. At the southern station, grazing by the whole mesozooplankton assemblage resulted in a removal of 14% of PP, and its effect on net phytoplankton growth rate was similar irrespective of ambient light. In contrast, reduction in light availability had an approximately 3-fold greater impact on net phytoplankton growth rate than mesozooplankton grazing pressure. The low mesozooplankton grazing impact across stations suggests limited mesozooplankton-mediated vertical export of phytoplankton production. The constraints provided here on trophic transfer, as well as quantitative estimates of the relative contribution of light and grazer controls of PP and of grazer-induced shifts in particle size spectra, illuminate food web dynamics and aid in parameterizing modeling-frameworks assessing global elemental fluxes and carbon export.
在春季对北大西洋西部表层中、微型浮游动物对浮游植物初级生产（PP）的影响进行了研究。在一个纬度断面的三个站位进行了船上实验，这些站位在混合层深度、温度和中型浮游动物分类组成方面存在差异。在北部和中部站位，中型浮游动物群落数量上以[具体种类1]为主，北部站位也有[具体种类2]。南部站位比其他站位温度高10℃以上，拥有最多样化的中型浮游动物组合，以小型桡足类为主，包括[具体种类3]等。仅在北部站位检测到微型浮游动物的摄食，其去除了97%的初级生产。[具体种类1]和[具体种类2]的估计清除率表明，在原位丰度下，这些中型浮游动物不太可能对浮游植物丰度产生重大影响，除非局部聚集。尽管中型浮游动物对总浮游植物的摄食影响最小，但这些捕食者完全去除了数量稀少的大于10μm的颗粒，改变了粒径谱。在南部站位，整个中型浮游动物组合的摄食导致去除了14%的初级生产，并且其对净浮游植物生长率的影响与环境光无关。相比之下，光照可用性的降低对净浮游植物生长率的影响比中型浮游动物的摄食压力大约大3倍。各站位中型浮游动物摄食影响较低表明浮游植物生产通过中型浮游动物介导的垂直输出有限。这里提供的对营养转移的限制，以及对光照和捕食者对初级生产的控制以及捕食者引起的粒径谱变化的相对贡献的定量估计，阐明了食物网动态，并有助于为评估全球元素通量和碳输出的建模框架设定参数。
