Diatom Blooms and Planktonic Grazers: Paradigm or Paradox?

硅藻华和浮游食草动物：范式还是悖论？

• 批准号: 0118044
• 负责人: Bruce Frost
• 金额: $ 47.03万
• 依托单位: University of Washington
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2001
• 资助国家: 美国
• 起止时间: 2001-10-01 至 2005-09-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0118044&HistoricalAwards=false
• 关键词: Diatom; Blooms; Planktonic; Grazers; Paradigm

Phytoplankton blooms are major events in the pelagic environment of temperate to subpolar coastal seas. Because blooms are large and relatively reliable seasonal pulses of food resources, the life histories of many pelagic consumer populations, both planktonic grazers and higher trophic level types such as fish, appear synchronized with them. Yet there is an apparent paradox. Results from numerous recent laboratory studies indicate that some species of diatoms, including species that may be biomass dominants during phytoplankton blooms, can inhibit egg production and/or embryonic and postembryonic development of several species of planktonic suspension-feeding copepods. The specific mechanism underlying the inhibition is currently under debate. Diatoms may be nutritionally deficient, but they also contain toxic substances that induce deleterious effects in copepods. However, the general relevance of these laboratory studies for natural populations of copepods is uncertain, as field investigations of the effects of diatom blooms have yielded contradictory results.The goal of this research project is to test in the sea the hypothesis that diatom-dominated phytoplankton blooms have inhibitory effects on egg production rate and/or postembryonic development of natural populations of the planktonic suspension-feeding copepods Calanus pacificus and Pseudocalanus newmani. The study will be done in Dabob Bay (Washington State) where intense, diatom-dominated phytoplankton blooms occur reliably in March. During these blooms, diatom concentrations reach or exceed levels known from laboratory studies to have deleterious effects on copepods. Previous field studies elsewhere of effects of diatom blooms on copepods have not met this condition. To test the hypothesis a combination of approaches is proposed: (1) observations on the distribution and abundance of copepods, diatoms, and other potential prey; (2) analysis of fecal pellets of adult copepods to verify that they are ingesting diatoms in situ; (3) experiments providing adequate control and replication to determine feeding rates of adult copepods on diatoms and other prey; (4) incubations to estimate in situ egg production rate and hatching success of both copepod species; (5) experiments to test for the direct effects of diatoms on egg production rate and hatching success and postembryonic development of the two copepod species. The possibility that diatoms may impact metazoan grazers such as copepods is of enormous basic and applied scientific interest. At a basic level, the problem is central to understanding the structure and function of marine planktonic systems. Any process by which phytoplankton inhibit reproduction or development of grazing zooplankton could markedly affect the pelagic food web well beyond the level of primary consumers. That is, a process affecting the population response of grazers would ramify through the food web, directly impacting other consumer species whose reproduction and growth depend on occurrence and abundance of eggs and immature stages of grazers. Thus, it is crucial to know whether diatoms are deleterious to natural populations of copepods and, if so, the specific nature of the effect, how frequently it occurs, and what the implications are for higher trophic levels.On a practical level, the magnitude of sustainable harvest of fish from the ocean is ultimately dependent not just on the level of primary production, but how that production is (or is not) transferred through the food web to higher (harvestable) trophic levels. An unambiguous test of the effects of diatom blooms on natural populations of planktonic grazers could therefore represent a major advance in understanding for pelagic biological oceanography.

浮游植物水华是温带至亚极地沿海海洋中上层环境中的重大事件。由于水华是食物资源的大型和相对可靠的季节性脉动，许多中上层消费种群的生活史似乎与它们同步，包括浮游食草动物和营养水平较高的类型，如鱼类。然而，这里面有一个明显的悖论。最近的大量实验室研究结果表明，一些种类的硅藻，包括在浮游植物水华期间可能是生物量优势的物种，可以抑制几种浮游悬浮摄食的桡足类动物的产卵和/或胚胎和胚胎后发育。这种抑制的具体机制目前正在辩论中。硅藻可能缺乏营养，但它们也含有对桡足类动物产生有害影响的有毒物质。然而，这些实验室研究与桡足类自然种群的总体相关性尚不确定，因为对硅藻水华影响的实地调查得出了相互矛盾的结果。本研究项目的目标是在海洋中检验硅藻主导的浮游植物水华对浮游暂停摄食的桡足类自然种群的产卵率和/或胚胎后发育具有抑制作用的假说。这项研究将在德博湾(华盛顿州)进行，那里以硅藻为主的强烈浮游植物水华在3月份可靠地出现。在这些水华期间，硅藻浓度达到或超过实验室研究已知的对桡足类产生有害影响的水平。以前在其他地方关于硅藻水华对桡足类动物影响的实地研究并不满足这一条件。为验证这一假说，提出了一系列方法：(1)观察桡足类、硅藻和其他潜在猎物的分布和丰度；(2)分析成年桡足类动物的粪便颗粒，以证实它们在原位摄食硅藻；(3)提供适当的控制和复制实验，以确定成年桡足类动物对硅藻和其他猎物的摄食率；(4)孵化以估计两个桡足类物种的就地产蛋率和孵化成功率；(5)测试硅藻对这两个桡足类物种产卵率、孵化成功和胚胎后发育的直接影响。硅藻可能会影响后生动物食草动物，如桡足类，这一可能性具有巨大的基础和应用科学价值。在基本层面上，这个问题是理解海洋浮游系统的结构和功能的核心。浮游植物抑制捕食性浮游动物繁殖或发展的任何过程都可能对远洋食物网产生重大影响，远远超出初级消费者的水平。也就是说，影响食草动物种群反应的过程将通过食物网产生分支，直接影响到其他消费物种，这些物种的繁殖和生长依赖于卵子的出现和丰富以及食草动物的未成熟阶段。因此，关键是要知道硅藻是否对桡足类自然种群有害，如果是的话，这种影响的具体性质，发生的频率，以及对更高的营养水平的影响。在实际水平上，从海洋可持续捕捞鱼类的规模最终不仅取决于初级生产水平，而且取决于这种生产如何通过食物网转移到(可收获的)更高的营养水平。因此，明确测试硅藻水华对浮游食草动物自然种群的影响可能是对远洋生物海洋学认识的重大进步。