Storm-Induced Predator-Prey Decoupling Promotes Springtime Accumulation of North Atlantic Phytoplankton
Storm-Induced Predator-Prey Decoupling Promotes Springtime Accumulation of North Atlantic Phytoplankton
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DOI：
10.3389/fmars.2019.00608
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发表时间：
2019-09-25
影响因子：
3.7
通讯作者：
Menden-Deuer, Susanne
中科院分区：
文献类型：
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作者：
Morison, Francoise;Harvey, Elizabeth;Menden-Deuer, Susanne
我们研究了北大西洋浮游生物种群动态对春季深层混合事件后地表水快速再分层的响应。在4天的时间里，我们测量了浮游植物的生长和食草动物/病毒引起的死亡率，稀释试验在一定范围的光强下进行。根据叶绿素a的变化和流式细胞术鉴定的三种浮游植物群的丰度来估计速率。最初，生物和物理水柱性质在100 - 200米以下是均匀的，随后混合层迅速浅化到20-30米。初始原位叶绿素a浓度为0.4 μ g -1，浮游植物生物量在接下来的2天内以平均0.4 d（-1）的速度积累。当混合层深度最大时，浮游植物无死亡损失，随光强的增加，浮游植物生长速率增加。浅滩化后，放牧率增加，但与浮游植物生长速率的幅度不匹配。当混合层最浅时，在所有非暗光强度下，生长速率均超过bbb1 d（-1）。基于叶绿素a的掠食率在不同光照水平下是一致的（类似于0.3 d(-1)），在聚球菌上最高（0.3-0.6 d(-1)），在微真核生物上最低（类似于0.2 d(-1)）。放牧恢复的延迟导致增长超过损失，平均消耗初级产量的30%。在所有混合剖面和光照强度下，病毒引起的死亡率最低。总体而言，船上实验预测的叶绿素a和特定群体的浮游植物积累率与原位实验结果相符，表明孵化条件忠实地捕捉了控制原位种群动态的生长和损失过程。研究结果表明，混合层的短暂加深和快速分层为浮游植物逃避原生生物的放牧和积累生物量提供了条件。在北大西洋的物理动态春季，混合深度的频繁短暂波动可能是控制北大西洋春季水华形成和规模的重要机制。
We examined the response of North Atlantic plankton population dynamics to rapid re-stratification of surface waters following a deep mixing event during spring. Over the 4-day occupation of a station, we measured phytoplankton growth and grazer/virus-induced mortality rates in dilution assays conducted across a range of light intensities. Rates were estimated from changes in chlorophyll a and the abundance of three phytoplankton groups identified by flow cytometry. Initially, biological and physical water column properties were homogeneous down to > 200 m, followed by rapid shoaling of the mixed layer to 20-30 m. Initial in situ chlorophyll a concentration was 0.4 mu g L-1, and phytoplankton biomass accumulated at an average rate of 0.4 d(-1) over the next 2 days. When mixed layer depth was maximal, there were no mortality losses and phytoplankton growth rates increased with increased light intensity. After shoaling, grazing rates increased, but never matched the magnitude of phytoplankton growth rates. When the mixed layer was shallowest, growth rates exceeded > 1 d(-1) at all non-dark light intensities. Chlorophyll a based grazing rates were consistent across light levels (similar to 0.3 d(-1)) and were highest on Synechococcus (0.3-0.6 d(-1)) and lowest on pico-eukaryotes (similar to 0.2 d(-1)). The delay with which grazing resumed resulted in growth exceeding losses and consumption of an average of 30% of primary production. Virus-induced mortality rates were minimal across all mixing profiles and light intensities. Overall, both chlorophyll a and group-specific phytoplankton accumulation rates predicted from the shipboard experiments matched those in situ, suggesting that incubation conditions faithfully captured the growth and loss processes governing in situ population dynamics. The observations made here indicate that transient deepening of the mixed layer followed by rapid stratification provided conditions under which phytoplankton escape protistan grazing and accumulate biomass. During the physically dynamic springtime in the North Atlantic, frequent ephemeral fluctuations in the depth of mixing may represent an important mechanism governing the formation and the magnitude of the North Atlantic spring bloom.