The role of antarctic marine protists in trophodynamics and global change and the impact of UV-B on these organisms - ASAC_40

This is a parent metadata record for work carried out as part of ASAC/AAS project 40.See the child metadata records for further information.More than 95% of the biomass in the Southern Ocean is microscopic - single celled plants, animals, bacteria and viruses. We are studying the factors that control their distribution and abundance - oceanographic and seasonal conditions, their physiology, and grazing - in order to model their vital roles as food for other organisms and their influence in moderating global climate change through absorption of CO2 and production of DMS. We are also addressing the changes expected in microbial communities through effects of climate change - global warming, sea ice retreat, ocean acidification and enhanced ultraviolet radiation.This project aims to determine the role of microorganisms in the Southern Ocean. The major objectives are to:* Identify and quantify key protistan components of the Southern Ocean ecosystem and study their autoecology.* Identify environmental and ecological processes that control abundance of key microbial components.* Determine interactions between key microbial components to quantify major pathways of carbon flow.* Determine the activity and viability of bacterioplankton and protists in the Southern Ocean.* Distinguish different microbial communities by identifying key taxa and associations so that processes such as primary production, respiration, grazing and particle flux can be readily parameterised in ecological models.* Determine the effect of elevated CO2 concentrations on microbial populations and processes.Taken from the 2008-2009 Progress Report:Progress against objectives:1. Ongoing sampling from Astrolabe has continued, with 3 return voyages being sampled for phytoplankton species, chlorophyll a and other pigments, coccolithophorid counts and DNA profiles, in conjunction with measurements of CO2, ocean structure, fluorescence and ocean colour by CSIRO / CRC colleagues. 2. Three sets of minicosm experiments were conducted at Davis station with 7 staff spending 4.5 - 5.5 months on site. These experiments consistently found that acidification caused blooms of nanoplanktonic diatoms and increased bacterial activity, apparently by inhibition of microheterotroph grazers, at the expense of larger cells that are more readily ingested by grazers such as krill. We showed for the first time in Antarctic waters that pCO2 affects the structure and function Antarctic microbial communities in a way that may reduce food availability to large grazers. Over 100 cultures of "winners and losers" from such experiments were isolated and returned to Australia. These will form the basis for further physiological experiments including molecular assays. 3. Submission and acceptance of 8 papers from the BROKE-West cruise (5 as senior author). These showed the interactions between bottom-up (micronutient) top-down (grazing) control in structuring microbial populations in the marginal ice zone. Five biogeographic zones were identified on the basis of species composition, and the productivity was measured for each zone. Microzooplankton grazing experiments found that grazing within that microbial loop consumed a significant proportion of new productivity. In some areas later in the season, all productivity was consumed by microheterotrophs, rather than metazoans such as krill. A time sequence was identified for seeding and development of components of ice edge blooms, subsequent grazing and decline and a mechanism postulated for export of micronutrients (e.g. iron) by grazing and sedimentation that prevents subsequent development of surface water blooms and constrains populations to a deep chlorophyll maximum below the level of a nutricline.4. Detailed analysis of greater than 30 strains of keystone species Emiliania huxleyi of two morphotypes in conjunction with Clara Hoppe (Masters student, Alfred Wegener Institute) and Suellen Cook (PhD student, University of Tasmania) showed consistent differences between strains in terms of pigmentation, responses to light and genetics. The two morphotypes appear to be adapted to different mixing regimes north and south of the Polar Front; the southern form may represent a new species.For a full list of references associated with this project, see the project link at the provided URL.

本记录为ASAC/AAS项目40相关研究工作的父级元数据记录（parent metadata record），详细信息请查阅其子级元数据记录。南大洋中超过95%的生物量为显微级单细胞生物，包括植物、动物、细菌与病毒。本研究旨在探究调控其分布与丰度的各类因素——包括海洋学与季节条件、自身生理特性以及捕食压力——以建模其作为其他生物食物的关键作用，以及其通过吸收二氧化碳（CO₂）、生成二甲基硫醚（DMS）来缓解全球气候变化的影响。此外，本研究还将探讨气候变化（全球变暖、海冰消退、海洋酸化与紫外辐射增强）对微生物群落造成的预期变化。

本项目旨在明确微生物在南大洋生态系统中的作用，主要研究目标包括：
1. 识别并量化南大洋生态系统中的核心原生生物类群，研究其个体生态学（autoecology）特性；
2. 识别调控核心微生物类群丰度的环境与生态过程；
3. 明确核心微生物类群间的相互作用，量化碳流动的主要途径；
4. 测定南大洋浮游细菌与原生生物的活性与存活力；
5. 通过识别关键类群与群落关联，区分不同的微生物群落，以便在生态模型中快速参数化初级生产、呼吸作用、捕食作用与颗粒通量等过程；
6. 测定升高的CO₂浓度对微生物种群与过程的影响。

以下内容摘选自2008-2009年度项目进展报告：
### 目标完成进展
1. 对“阿斯托拉贝号”（Astrolabe）的持续采样工作仍在进行中，已完成3次往返航次的采样，涵盖浮游植物物种、叶绿素a及其他色素、颗石藻计数与DNA图谱分析，同时与澳大利亚联邦科学与工业研究组织（Commonwealth Scientific and Industrial Research Organisation, CSIRO）、合作研究中心（Cooperative Research Centre, CRC）的合作者同步开展CO₂浓度、海洋结构、荧光与海洋水色的测定工作。
2. 在戴维斯站（Davis station）开展了3组微型生态系统实验，共有7名科研人员在站工作4.5至5.5个月。实验结果一致表明，海洋酸化会导致微型浮游硅藻水华爆发并提升细菌活性，其机制可能为抑制微型异养捕食者，使得更易被磷虾等捕食者摄食的大型细胞数量减少。本研究首次在南极海域证实，分压升高的CO₂（pCO₂）会改变南极微生物群落的结构与功能，进而可能降低大型捕食者可获取的食物量。我们从这类实验中分离得到了超过100株“优势种与劣势种”菌株并带回澳大利亚，后续将以此为基础开展包括分子检测在内的生理学实验。
3. 提交并接收了8篇来自BROKE-West航次的学术论文（其中5篇以通讯作者身份发表），这些论文阐明了自下而上（微量营养元素）与自上而下（捕食作用）的调控过程在边缘冰区微生物种群结构塑造中的相互作用。研究基于物种组成划定了5个生物地理分区，并测定了每个分区的生产力。微型浮游动物捕食实验发现，微生物环（microbial loop）的捕食作用消耗了相当比例的新生生产力；在部分区域的生长季后期，全部生产力均被微型异养生物消耗，而非磷虾等后生动物。研究还确定了冰缘水华组分的定植、后续捕食与衰退的时间序列，并提出了一种机制：捕食与沉降作用会输出微量营养元素（如铁），从而抑制后续表层水华的形成，并将种群限制在营养跃层下方的深层叶绿素最大值区域。
4. 与克拉拉·霍普（Clara Hoppe，阿尔弗雷德·魏格纳研究所硕士研究生）、休琳·库克（Suellen Cook，塔斯马尼亚大学博士研究生）合作，对两种形态型的30余株关键物种赫氏颗石藻（Emiliania huxleyi）进行了详细分析，结果显示不同菌株在色素沉着、光响应与遗传特性上存在稳定差异。这两种形态型似乎适应了极锋（Polar Front）南北两侧不同的混合环境，其中南部形态型可能代表一个新物种。

如需获取本项目相关的完整参考文献列表，请访问指定URL中的项目链接。