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Project Topic
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Coastal tidal sediments are highly productive ecosystems at the land-sea interface. Their productivity is often dominated by microbial biofilms, highly diverse consortia of benthic micro-organisms, embedded in a complex matrix of biogenic extracellular polymers. These biofilms support multiple ecosystem functions and services: they fuel coastal food webs (including commercial fisheries and shellfish farming), they drive carbon fluxes across the sediment-water interface, and they stabilize sediments. In these sediments, primary production of benthic microalgae is rapidly respired in the sediment food web or is resuspended. Many unknowns however remain regarding the tidal flat carbon cycle, but most importantly, there is a striking lack of knowledge about tidal sediment microbial biodiversity, and how this biodiversity affects the ecosystem functioning of these systems (the BEF relation). Tidal flat microbial biodiversity is structured by hydrodynamic disturbance which creates gradients in sediment composition (from sandy to silty), and by trophic and non-trophic interactions between organisms. The overarching objective of the BIO-Tide project is to identify and quantify the relation between microbial biodiversity and carbon cycle related ecosystem functions in contrasting tidal flat environments (sand vs silt) in the explicit context of biotic interactions. Focus will thus be on the carbon cycle and ecosystem functions which are directly implicated in (e.g. primary and secondary production, extracellular polymer substance production) or indirectly dependent on this cycle (sediment stability). The project will be articulated in 7 work packages. Field and laboratory experiments (WP1-4) in combination with inverse modelling (WP5) will allow assessing how microbial biodiversity is related to tidal flat carbon cycling and which organisms and functional groups are involved. Two large-scale field experiments, carried out in two different tidal flat systems, will provide a detailed description and quantification of the relation between microbial, meio- and macrobenthic taxonomic and functional diversity on the one hand and carbon fluxes on the other in contrasting tidal flat sediments, and this at high taxonomic and functional resolution (WP1). This will be achieved using a combination of state-of-the-art techniques for the characterization of microbial diversity (next generation sequencing based omics) and microbial activity in stable isotope probing experiments (RNA-SIP, CSIA-SIP and nanoSIMS). The laboratory experiments (WP2-4) will enhance our understanding of the mechanisms underlying these BEF relations, and are specifically aimed at addressing the role of microbial biodiversity in little-known pathways in the tidal flat carbon cycle, such as such benthic microalgal mixotrophy, protozoan grazing, the uptake of biogenic extracellular polymers by unicellular eukaryotes, and the importance of microalgal diversity for the growth of macrobenthos (i.c. the commercially important oyster). The WP1-4 data will feed into linear inverse models developed in WP5 which will be used to model the sedimentary carbon cycle at a high level of functional detail. Comparison of the results of the two field campaigns, the mechanistic BEF insights obtained in WP2-4 and the inverse models of WP5 will allow identifying general and emergent patterns in tidal flat BEF relations and will help addressing potential contextual variation in these patterns. This information will be crucial for evaluating to what degree our results can be extrapolated to the scale of whole tidal flat ecosystems using RS approaches (WP6). WP7 will oversee the management of the project. Given the huge importance of tidal flat ecosystems in coastal areas, we aim at close collaboration (at different levels of engagement) with public and private stakeholders throughout the project in order to maximize socio-economic valorisation of the results.
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