Role of meio- and macrofauna in benthic ecosystem functioning: Testing effects of different ice cover regimes

南极洲周围的许多生态系统正在经历快速变化，特别是在冰盖动态方面。目前尚不清楚这种发展是否以及如何影响海底的过程，即底栖生物的功能。因此，为了全面了解生态系统的功能，有必要确定不同的生态系统组成部分（如动物群落群）在变化和稳定的冰盖制度下对海底过程的作用。很少有研究同时调查底栖环境中不同大小的生物类别和群落，如小型和大型动物。没有人研究过它们对底栖动物功能的补充作用。冰盖的减少或变化对小型和大型动物类群之间的营养相互作用及其相对重要性的影响尚不清楚。底栖生物边界通量（铵、硝酸盐、磷酸盐、硅酸、氧）如何受到威德尔海不同冰盖制度的影响尚不清楚。实际上，我们对南大洋中小底生和大底栖生物群落间的有机物再矿化分配一无所知。在这个为期3年的项目中，我们建议共同评估威德尔海和南极半岛附近底栖生态系统功能对冰盖状态及其变化的响应。为了更好地理解不同大小的隔间及其相关分类群在沉积物系统中的特殊作用，我们需要确定(1)在不同冰制地区，小型和大型动物群落结构对食物摄取和底栖动物再矿化的作用；(2)冰制变化导致的食物输入变化对底栖动物功能-动物大小隔间关系的影响。这两个互补的方面将作为两个工作包与一名联合博士生一起研究，导致第三个综合工作包。RV北极星号ps81号（2013年3月22日至18日）前往南极半岛周围，ps96号（2015年12月6日至2016年2月14日）前往威德尔海东南部。取样区包括冰盖减少、变化和持续的地点。因此，我们可以研究这两个底栖区室的再矿化效率，并将其与不同地区小动物和大型动物类群的食物网位置联系起来。此外，我们在自然和复制的脉冲追逐实验条件下，实验测试了沉积物-水界面和营养相互作用的再矿化反应（底栖生物边界通量和食物摄取）。在第三个（综合）工作包中，我们将构建一个评估南大洋底栖生物生态功能的概念模型。通过首次将动物大小分类和不同底栖生物过程同步结合起来，将有可能评估海冰覆盖制度变化对威德尔海底栖生物系统的净生态影响。

Many ecosystems around Antarctica are undergoing rapid changes, particularly in ice cover dynamics. It is not known if and how this development influences the processes at the seafloor, the benthic functions. For a comprehensive understanding of ecosystem functioning it is, hence, necessary to determine the role of different ecosystem components (e.g. faunal community groups) for seafloor processes under changing and stable ice cover regimes. Few studies have investigated different size classes and communities of organisms, like meio- and macrofauna, in this benthic environment simultaneously. And none has studied their complementary role for benthic functions. Influences of reduced or changing ice cover on trophic interactions among and the relative importance of meio- and macrofauna taxa are not understood. How benthic boundary fluxes (ammonium, nitrate, phosphate, silicic acid, oxygen) are affected by different ice cover regimes in the Weddell Sea is unknown. And virtually nothing is known about the partitioning of organic matter remineralisation between the meiobenthic and macrobenthic community compartment in the Southern Ocean. In this 3-year project, we propose to jointly evaluate the response of benthic ecosystem functioning to ice cover regimes and their changes in the Weddell Sea and the vicinity of the Antarctic Peninsula. To better understand the particular roles of the different size compartments and their associated taxa in the sediment system we need to determine (1) the role of meio- and macrofauna community structure for food uptake and benthic remineralisation in regions with different ice regimes and (2) the effect of variations in food input as a result of changing ice regimes on this benthic function - faunal size compartment relation.The two complementary aspects will be studied as two work packages with one joint doctoral student, leading to a third synthesis work package. Samples are available from the expeditions of RV Polarstern PS 81 (22.01 to 18.03.2013) to around the Antarctic Peninsula and PS 96 (06.12.2015 to 14.02.2016) to the south eastern Weddell Sea. The sampled area includes sites with reduced, variable and lasting ice cover regime. Thus, we can study remineralisation efficiency of both benthic compartments and relate it to food web position of meio- and macrofauna taxa in different regions. Further, we experimentally test remineralisation response (benthic boundary fluxes and food uptake) at the sediment-water interface and trophic interactions under natural and replicated pulse-chase experimental conditions. In the third (synthesis) work package we will construct a conceptual model for the evaluation of benthic ecological functioning in the Southern Ocean. By combining faunal size classes and different benthic processes synchronously for the first time, it will be possible to evaluate, what the net ecological effect of changing ice cover regimes on the Weddell Sea benthic system could be.