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

• Applicants: Dr. Heike Link; Dr. Gritta Veit-Köhler
• Subject Area: Oceanography
• Term: from 2017 to 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 365901123

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.

• DFG Programme: Infrastructure Priority Programmes
• Subproject of: SPP 1158: Infrastructure area - Antarctic Research with Comparative Investigations in Arctic Sea Ice Areas
• Co-Investigator: Privatdozent Dr. Stefan Forster