No abstract

The importance of macrobenthos in benthic‐pelagic coupling and early diagenesis of organic carbon has long been recognized but has not been quantified at a regional scale. By using the southern North Sea as an exemplary area we present a modeling attempt to quantify the budget of total organic carbon (TOC) reworked by macrobenthos in seafloor surface sediments. Vertical profiles in sediments collected in the field indicate a significant but nonlinear correlation between TOC and macrobenthic biomass. A mechanistic model is used to resolve the bidirectional interaction between TOC and macrobenthos. A novelty of this model is that bioturbation is resolved dynamically depending on variations in local food resource and macrobenthic biomass. The model is coupled to 3‐D hydrodynamic‐biogeochemical simulations to hindcast the mutual dependence between sedimentary TOC and macrobenthos from 1948 to 2015. Agreement with field data reveals a satisfactory model performance. Our simulations show that the preservation of TOC in the North Sea sediments is determined not only by pelagic conditions (hydrodynamic regime and primary production) but also by the vertical distribution of TOC, bioturbation intensity, and the vertical positioning of macrobenthos. Macrobenthos annually ingest 20–35% and in addition vertically diffuse 11–22% of the total budget of TOC in the uppermost 30‐cm sediments in the southern North Sea. This result indicates a central role of benthic animals in modulating the organic carbon cycling at the sediment‐water interface of continental margins.

Bioturbation is one of the key mediators of biogeochemical processes in benthic habitats that can have a high contribution to seafloor functioning and benthic pelagic coupling in coastal waters. Previous studies on bioturbation were limited to point locations and extrapolations in single regions, but have not accounted for regional differences under changing environmental conditions, though there are indications that species contributions will differ across regions or with biotic and abiotic context. To capture those differences and assess global patterns and commonalities, multi-regional analyses are imperative. Here for the first time, bioturbation potential (BPc), a functional indicator of benthic community bioturbation, was estimated based on macrofauna data from four regions (i.e. German Baltic Sea, German North Sea, Belgian part of the North Sea and the Eastern English Channel). For each region and sediment type we identified key species contributing to BPc. Comparison within and across regions demonstrated regional differences, and both overlap and mismatch between species that are functionally important and those that are dominant in biomass. Knowledge on the functionally important species is crucial when management objectives include the protection of certain ecosystem functions. Available environmental layers were used as predictors to model the spatial distribution of BPc for each area and to explore the underlying drivers of differences. Random forest models were trained using as response variables either i) BPc initially calculated per station; or ii) BPpthe species-specific contribution to BPcfor key species Please note that this is an author-produced PDF of an article accepted for publication following peer review. The definitive publisher-authenticated version is available on the publisher Web site. (with subsequent summation of their predicted full-coverage distributions to BPc). Maps of BPc distribution predicted by random forest were compared with those generated using natural neighbour interpolation. Overall, derived BPc values increased towards the German parts of the North and Baltic Seas. The relevance of BPc for ecosystem processes and functions, however, vary with biotic and abiotic settings. Results revealed a strong association of BPc with species diversity and region, but less with sediment grain size. A large range of BPc occurred when species richness was low. This suggests that the provisioning of high bioturbation activity is possible also under low diversity, where it is vulnerable due to reduced resilience. The executed multi-regional analysis allowed identifying regional differences in performance of macrofauna, suggesting the need for region-specific conservation and management strategies. Highlights ► First multi-regional analysis of macrofauna community bioturbation potential (BPc). ► Functionally important key species differ regionally and between sediments. ► Overall BPc values decreased from the Baltic Sea towards Eastern English Channel. ► Relevance of BPc for ecosystem f...