Sponge skeletons as an important sink of silicon in the global oceans

International audienceSilicon (Si) is a pivotal element in the biogeochemical and ecological functioning of the ocean. The marine Si cycle is thought to be in internal equilibrium, but the recent discovery of Si entries through groundwater and glacial melting have increased the known Si inputs relative to the outputs in the global oceans. Known outputs are due to the burying of diatom skeletons or their conversion into authigenic clay by reverse weathering. Here we show that non-phototrophic organisms, such as sponges and radiolarians, also facilitate significant Si burial through their siliceous skeletons. Microscopic examination and digestion of sediments revealed that most burial occurs through sponge skeletons, which, being unusually resistant to dissolution, had passed unnoticed in the biogeochemical inventories of sediments. The preservation of sponge spicules in sediments was 45.2 +/- 27.4%, but only 6.8 +/- 10.1% for radiolarian testa and 8% for diatom frustules. Sponges lead to a global burial flux of 1.71 +/- 1.61TmolSi yr(-1) and only 0.09 +/- 0.05 TmolSi yr(-1) occurs through radiolarians. Collectively, these two non-phototrophically produced silicas increase the Si output of the ocean to 12.8 TmolSi yr(-1), which accounts for a previously ignored sink that is necessary to adequately assess the global balance of the marine Si cycle

European Broad-Scale Seabed Habitat Maps Support Implementation of Ecosystem-Based Management

We have analyzed the development of “Broad-Scale Seabed Habitat Maps” (BSHM) and their potential use in a European context with regard to the EU Marine Strategy Framework Directive (MSFD) implementation, MPA designation and network assessment as well as other applications of BSHMs. The analyses are anchored in BSHMs developed by a series of interlinked EU projects (e.g. UKSeaMap, BALANCE, MESH, Mesh Atlantic, EUSeaMap 2012, and EUSeaMap 2016) and all maps are based on environmental data. Some EU Member States have used BSHMs as part of their MSFD Initial Assessments published in 2012. However, we conclude that BSHMs are a prerequisite for another key MSFD activity, i.e. mapping of potentially cumulative effects of multiple human stressors. Further, BSHMs seem to play a growing role with regard to evidence-based assessments of MPAs. With the upcoming second round of MSFD Initial Assessments due in 2018, including assessment of potentially cumulative pressures, there seems to be an increasing need for more BSHMs nationally, regionally and on a European scale