The size spectrum of phytoplankton: a key parameter for water quality and ecosystem function.

构成浮游植物的各种生物只占全球光合作用生物量的2%，但由于它们的高增长率，它们贡献了每年全球碳固定的近一半。根据浮游植物的大小、分类组成和生化特性，可将其划分为不同的功能群。在海洋食物网中，大小是碳周转、营养吸收和营养转移效率的重要参数。浮游植物采用了三个主要大小类别：微微浮游生物(小于2微米)、纳米浮游生物(介于2至20微米之间)和净浮游生物(大于20微米)。一般而言，在常规监测方案中，只考虑较大的微型浮游生物和净浮游生物。因此，现有的模式是，英国沿海水域浮游植物的年度生产周期始于硅藻的春季开花，紧随其后的是甲藻的夏季优势。然而，过去几年光学和分子技术的进步表明，微微浮游生物和纳米浮游生物可能非常丰富，例如占南大洋98%的生产性生物量。最近于2007年前往北海中部的邮轮使用色素分析表明，浮游植物功能类型(PFT)，如金藻、苔藓植物、硅藻和微囊藻在不同时期均可占优势(CEFAS，未发表)。今天，商业上可用的技术的进步使我们能够从部门到物种层面快速计算和识别大量微微和纳米浮游生物样本。在这项提案中，我们将使用细胞学分析、色素指纹分析和分子工具来促进我们对沿海水域浮游植物生态的了解。对于这个博士生，我们的目标是评估浮游植物功能类型在一系列空间和时间尺度上的自然变异性，将PFT分布与环境参数联系起来，并测试观察到的分布模式是否可以用现有的理论来解释。在研究的第一部分，学生将熟悉这些技术。流式细胞术现在是根据浮游植物的形状、大小和色素组成对浮游植物进行计数和分析的一种成熟的方法。UEA和CEFA都提供了仪器。用于这项工作的主要仪器是CEFAS CytoSense(CytoBuoy，BV.)这是一种多功能、便携式台式流式细胞仪，能够测量长度从1微米到500微米以上的细胞。浮游植物培养将被用来建立一个细胞图库，作为天然样品的参考。将开发荧光杂交技术(COD-FISH、TSA-FISH)，以确定研究中不同水体中微米和纳米浮游生物中主要官能团的比例。此外，辅助颜料的测量将加强可用于识别不同官能团的信息。这些结合的技术将使学生能够继续研究的第二部分，这将涉及到对自然产生的浮游植物群落进行分类。这将需要在多元统计方面进行适当的培训。这项工作将在从沿海水域到公海的英国陆架海的大空间尺度上进行，并具有高度的可重复性。学生将有几次机会访问北海、爱尔兰海和凯尔特海的不同采样区(例如CEFAS RV Endeavour底栖鱼调查)，每月从英格兰东海岸沿线地区获得样本(来自环境署的水框架指令监测计划)。地理上的变化将伴随着每日水样测量的时间变化，而自动系统(智能浮标网络)是由CEFAS维护的。

The diverse group of organisms forming the phytoplankton represents just 2% of global photosynthetic biomass, but due to their high growth rates they contribute almost a half of annual global carbon fixation. The phytoplankton can be divided into different functional groups according to their size, taxonomic composition and biochemical properties. Size is an important parameter in terms of carbon turnover, nutrient uptake and efficiency of trophic transfer in the marine food web. Three main size categories have been adopted for the phytoplankton: picoplankton (smaller than 2 microns), nanoplankton (between 2 and 20 microns) and net plankton (larger than 20 microns). Generally in routine monitoring programmes, only the larger nanoplankton and net plankton are taken into account. Thus, the existing paradigm is that the annual production cycle of phytoplankton in U.K. coastal waters commences with a spring bloom of diatoms, followed by summer dominance of dinoflagellates. However, advances in optical and molecular techniques in the last few years have demonstrated that pico- and nanoplankton can be very abundant, representing for example 98% of the productive biomass in the Southern Ocean. Recent cruises to the central North Sea in 2007 have used pigment analysis to show that phytoplankton functional types (PFT) such as chrysophytes, prymesiophytes, diatoms and picocyanobacteria can all be dominant at different times (CEFAS, unpublished). Today, the improvements in commercially available technology allow us to quickly count and identify, from division to species level, a large numbers of pico and nanoplankton samples. In this proposal we will use cytometric analysis together with pigment fingerprinting and molecular tools to advance our knowledge of phytoplankton ecology in coastal waters. For this PhD studentship our aims are to assess the natural variability in phytoplankton functional types at a range of spatial and temporal scales, to relate PFT distribution to environmental parameters and to test whether the observed patterns of distribution can be explained by existing theories. In the first part of the study the student will be familiarised with the techniques. Flow cytometry is now a well-established method for counting and analysing phytoplankton according to their shape, size and pigment composition. Instruments are available at both UEA and Cefas. The primary instrument to be used for this work is the CEFAS CytoSense (Cytobuoy, BV.) which is a versatile, portable bench-top flow cytometer capable of measuring cells from 1 to over 500 microns in length. Phytoplankton cultures will be used to establish a library of cytograms to be used as a reference for natural samples. Fluorescence hybridisation techniques (COD-FISH, TSA-FISH) will be developed to determine the proportion of the main functional groups in the pico and nanoplankton in the different water bodies of the study. Additionally, the measurement of accessory pigments will reinforce the information available for the identification of the different functional groups. These combined techniques will allow the student to pursue the second part of the study which will involve classifying the naturally occurring phytoplankton communities. This will necessitate appropriate training in multivariate statistics. The work will be done across large spatial scales in U.K. shelf seas from coastal waters to the open ocean, and with a high level of replication. Several opportunities will be available to the student to access different sampling areas from the North Sea, Irish Sea and Celtic Sea (e.g. the CEFAS RV Endeavour Ground Fish Surveys), to receive samples from localities along the East coast of England every month (from the Environment Agency's Water Framework Directive monitoring programme). The geographical variation will be coupled by a temporal variation of measurements from daily water sampling with an automatic system (SmartBuoy network) maintained by CEFAS.