Sources of Particulate Organic Matter and their use by Benthic Suspension-feeders in the Coastal California Ecosystem

智力优势：如果我们要预测食物网在面对环境变化时可能发生的变化，就必须了解营养联系以及资源变异性如何影响消费者。大型藻类和浮游植物支持高生产力的海洋生态系统。基于稳定同位素分析的研究支持这样一种观点，即大型藻类碎屑，特别是巨型海带Macrocystis，是底栖悬浮物饲养者膳食碳的主要来源。然而，最近的调查结果的四年稳定同位素研究表明，浮游植物，而不是海带，是底栖悬浮物的主要食物来源，在圣巴巴拉海峡的珊瑚礁，浮游植物丰度的变化，结合喂养的选择性和消费者组织周转时间的规模，可能会驱动消费者同位素值的变化。 结果表明，在过去20年中，沿海生态系统的“快照”同位素研究中的一个关键假设，即沿海浮游植物的同位素特征可以由近海浮游植物的同位素特征来代表，可能是不正确的。之所以做出这种假设，是因为很难将浮游植物与碎屑分离，以获得未受污染的同位素特征，这在淡水系统中也是一个问题。研究人员将解决两个主要目标，在这个研究项目：1）确定浮游植物和巨型海带碎屑的贡献池悬浮礁POM和POM组成是否随距离海带森林，和2）评估如何不同的组件的POM被用作食物的礁悬浮馈线。 两种互补的方法，旨在探讨在沿海沃茨的POM的浮游植物和海带碎屑的贡献：一个先进的流式细胞术和细胞分选系统，以分离浮游植物从散装POM，和分析的POM和消费者的必需多不饱和脂肪酸（PUFA）。 研究人员已经获得了初步数据，证明了这两种方法的可行性。孤立的近岸浮游植物和海带，化合物特定的多不饱和脂肪酸的同位素值，将被用于混合模型，以估计这两个主要的初级生产者悬浮饲料的相对贡献。 两个假设的机制，可能会影响消费者的同位素组成也将进行测试：选择性喂养的POM的特定馏分，和组织周转时间。该项目将为底栖悬浮摄食者的营养支持提供新的见解，底栖悬浮摄食者是沿海生态系统中具有生态和经济重要性的群体。结果将测试的一般假设，即巨型海带碎屑是一个重要的膳食碳源悬浮饲料，一个普遍接受的想法，需要重新评估的关键假设，已在其支持。稳定同位素分析是检验这一假设的理想工具，因为在我们的研究地点，浮游植物和巨型海带的丰度存在时空尺度的变化。 采样方案与圣巴巴拉沿海LTER提供的生产者生物量的长期数据相结合，将使调查人员能够捕捉到这种变异性，而基于"快照"稳定同位素分析的研究通常会遗漏这种变异性。

Intellectual Merit: Understanding trophic connections and how resource variability affects consumers is necessary if we are to predict how food webs may shift in the face of environmental change. Macroalgae and phytoplankton support highly productive marine ecosystems. Research based on stable isotope analyses has supported the idea that macroalgal detritus, especially the giant kelp Macrocystis, is a major source of dietary carbon to benthic suspension-feeders. However, recent findings by the investigator's four-year stable isotope study suggest that phytoplankton, not kelp, are the main food resource for benthic suspension-feeders on reefs in the Santa Barbara Channel, and that variation in phytoplankton abundance, combined with feeding selectivity and the scale of consumer tissue turnover times, may drive variability in consumer isotope values. The results suggest that a key assumption made in 'snapshot' isotope studies of coastal ecosystems over the past 20 years, which the isotope signature of coastal phytoplankton can be represented by that of offshore phytoplankton, could be incorrect. This assumption has been made because of the difficulty in separating phytoplankton from detritus to obtain an uncontaminated isotope signature, also a problem in freshwater systems. The investigator will address two main objectives in this research project: 1) determining the contribution of phytoplankton and giant kelp detritus to the pool of suspended reef POM and whether POM composition varies with distance from kelp forests, and 2) evaluating how different components of the POM are used as food by reef suspension feeders. Two complementary approaches are designed to explore the contribution of phytoplankton and kelp detritus to POM in coastal waters: an advanced flow cytometry and cell-sorting system to separate phytoplankton from bulk POM, and analysis of essential polyunsaturated fatty acids (PUFA) in POM and consumers. The investigators have obtained preliminary data that demonstrate the feasibility of both of these methods. Isotope values of isolated inshore phytoplankton and kelp, and compound-specific PUFA, will be used in mixing models to estimate relative contributions of these two major primary producers to suspension feeder diets. Two hypothesized mechanisms that may influence isotopic composition of consumers will also be tested: selective feeding on particular fractions of the POM, and tissue turnover times. This project will provide new insights into the trophic support of benthic suspension feeders, an ecologically and economically important guild in coastal ecosystems. The results will test the general hypothesis that giant kelp detritus is an important source of dietary carbon to suspension feeders, a commonly accepted idea that needs re-evaluation in light of key assumptions that have been made in its support. Stable isotope analyses are an ideal tool for testing this hypothesis given the spatial and temporal scales of variability that exist in the abundance of phytoplankton and giant kelp at our study sites. The sampling scheme combined with longer-term data on producer biomass provided by the Santa Barbara Coastal LTER will enable the investigators to capture this variability, which is generally missed by studies based on 'snapshot' stable isotope analyses.