Phytoplankton growth and grazing dynamics during anomalous heat wave and suppressed upwelling conditions in the southern California Current

IF 2.3 3区 地球科学 Q2 OCEANOGRAPHY
Michael R. Landry , Alexandra L. Freibott , Michael R. Stukel , Karen E. Selph , Andrew E. Allen , Ariel Rabines
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Abstract

We investigated phytoplankton dynamics in the southern California Current System (SCCS) in August 2014 during the early phase of the 2014-15 marine heat wave (MHW). Multi-day experiments were conducted at three inshore and two offshore sites, with daily depth profiles of dilution incubations on a drifting array to determine growth and grazing rates and shipboard assessments of nutrient effects. Picophytoplankton populations were analyzed by flow cytometry and eukaryotic phytoplankton by 18 S sequencing. Mixed-layer nutrients were low across the region, but inshore sites had substantial nitrate concentrations and prominent Chla maxima in the lower euphotic zone. Shoreward transport of warm-stratified waters from the offshore suppressed coastal upwelling and shifted picophytoplankton distributions toward increased onshore abundance of Prochlorococcus and decreased Synechococcus and picoeukaryotes. These trends were reinforced by higher-than-average growth of Prochlorococcus at inshore sites and higher grazing of Synechococcus and picoeukaryotes. Prasinophytes (Chlorophyceae) were notably important among eukaryotic taxa, and pennates replaced centric taxa as the dominant diatoms in inshore waters compared to normal upwelling. Despite substantial spatial variability in community composition, offshore and inshore experimental locations both showed growth-grazing balances, with microzooplankton consuming similar percentages (80%) of primary production. We thus confirm expectations that the 2014-15 MHW resulted in greater trophic flow through the microbial food web at the expense of reduced direct phytoplankton (Chla) consumption by mesozooplankton. However, impacts on mesozooplankton energy budgets were partially offset by increased trophic flow through protistan microzooplankton and higher phytoplankton C:Chla.

南加州洋流异常热浪和抑制上升流条件下的浮游植物生长和放牧动力学
2014 年 8 月,在 2014-15 年海洋热浪(MHW)的早期阶段,我们调查了南加州洋流系统(SCCS)的浮游植物动态。我们在三个近岸地点和两个离岸地点进行了多天实验,每天在漂流阵列上进行深度剖面稀释培养,以确定生长率和放牧率,并在船上评估营养物质的影响。用流式细胞仪分析了浮游微藻种群,用 18 S 测序分析了浮游真核细胞。整个区域的混合层营养物质含量较低,但近岸地点的硝酸盐浓度较高,且在下极光带有明显的 Chla 最大值。从近海向岸输送的暖分层水抑制了沿岸上升流,并改变了浮游植物的分布,使原绿球藻在岸上的丰度增加,而 Synechococcus 和微小核藻则减少。在近岸地点,原绿球藻的生长量高于平均水平,而Synechococcus和皮浮游动物的摄食量则更高,从而加强了这些趋势。与正常上升流相比,真核生物类群中明显重要的是叶绿藻类(Prasinophytes),而在近岸水域,纤毛虫类取代了中心类群,成为主要的硅藻类群。尽管群落组成在空间上存在很大差异,但近海和近岸实验地点都显示出生长-掠夺平衡,微型浮游动物消耗了初级生产的相似百分比(80%)。因此,我们证实了以下预期:2014-15 年的 MHW 导致微生物食物网中的营养流增加,而中浮游动物对浮游植物(Chla)的直接消耗减少。然而,通过原生动物微浮游生物的营养流增加以及浮游植物 C:Chla 增加,部分抵消了对中浮游动物能量预算的影响。
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来源期刊
CiteScore
4.60
自引率
4.20%
发文量
144
审稿时长
18.3 weeks
期刊介绍: Deep-Sea Research Part I: Oceanographic Research Papers is devoted to the publication of the results of original scientific research, including theoretical work of evident oceanographic applicability; and the solution of instrumental or methodological problems with evidence of successful use. The journal is distinguished by its interdisciplinary nature and its breadth, covering the geological, physical, chemical and biological aspects of the ocean and its boundaries with the sea floor and the atmosphere. In addition to regular "Research Papers" and "Instruments and Methods" papers, briefer communications may be published as "Notes". Supplemental matter, such as extensive data tables or graphs and multimedia content, may be published as electronic appendices.
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