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Benthic fauna actively redistributes particles, water, and solutes in the sediment, contributing to the spatial and temporal heterogeneity of oxic, anoxic, and oscillatory redox zones.  The infaunal activity can also increase solute exchange between the sediment and the overlying water, but the underlying drivers and process rates vary among functional groups through their bioturbation, bioirrigation, feeding, and excretion, affecting the diffusional fluxes and benthic pelagic-coupling (Fig. 1).  These physical and chemical changes in the sediments by faunal activity have important implications for microbial assemblages, and the ecosystem processes they affect (e.g., organic matter mineralization and burial, and nutrient transformation pathways).  However, most biogeochemical models simplify and average variability in biologically-mediated processes that transform food (organic matter) into living tissue, respire oxygen, and release carbon dioxide.  This is mainly due to the difficulty to sample the seafloor (especially the deep sea) and the rarity of functional information on the benthic fauna, but more importantly, is the lack of collaboration between geochemists and biologists.

In a new study published by Snelgrove et al., an international group of benthic ecologists and geochemists attempt to elucidate the effect of benthic faunal activity on global seafloor carbon cycling.   Dr. Chih-Lin Wei, a benthic ecologist from IONTU, said, “We met in Stazione Zoologica Anton Dohrn Napoli, the oldest marine lab in the world.  We brainstormed for days because there were really not much global data on the biology of the seafloor, but the atmosphere of the lab kept you up because you can feel its connection with the history of marine biology”.  Eventually, the group analyzed and compared global carbon turnover rates using two different approaches.  One based on algorithm describing the decay of sinking organic carbon depositing on the seafloor and another based on carbon remineralization of sediment fauna (Fig. 2).  The main discrepancy is that one ignores and another considers the sediment biological activities.  Dr. Wei added, “We showed that the two approaches generate divergent outcomes in their global distribution, suggesting that adding even simple elements of seafloor ecology can dramatically change our view on the global seafloor carbon cycling”.  Their works also have an important implication on the interpretation of global biogeochemical cycles.  None of the current global climate change projections (e.g., Intergovernmental Panel on Climate Change; IPCC) and ecosystem service assessments (e.g., Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services; IPBES) have considered the effects of seafloor biological activities.  This means that our anticipation of climate changes (which often based on climate model outputs) and thus the societal decisions on mitigation and adaptation to climate changes can be greatly improved by considering the seafloor perspective.

Snelgrove, P.V.R.*, Soetaert, K., Solan, M., Thrush, S., Wei, C.-L., Danovaro, R., Fulweiler, R., Kitazato, H., Ingole, B., Norkko, A, Parkes, R.J., Volkenborn, N. (2018) Global Carbon Cycling on a Heterogeneous Seafloor. Trends in Ecology & Evolution. 33(2):96-105

http://dx.doi.org/10.1016/j.tree.2017.11.004

Figure 1. Global Map of Carbon Turnover on the Seafloor. (A) Biogeochemical turnover as estimated based on the aging of pelagically produced sinking organic matter on the seafloor. (B) Biological turnover of benthic organisms, estimated as the infauna respiration rate divided by the biomass; dots represent respiration data. (C) Comparison of turnover rates based on biogeochemical and biological models where light-green colors indicate coherence between models, warm colors indicate higher estimates for the biogeochemical model, and cool colors indicate higher estimates for the biological model. (D) No correlation between biological and biogeochemicl turnover estimates (log-log scale).

Figure 2. Global Map of Carbon Turnover on the Seafloor. (A) Biogeochemical turnover as estimated based on the aging of pelagically produced sinking organic matter on the seafloor. (B) Biological turnover of benthic organisms, estimated as the infauna respiration rate divided by the biomass; dots represent respiration data. (C) Comparison of turnover rates based on biogeochemical and biological models where light-green colors indicate coherence between models, warm colors indicate higher estimates for the biogeochemical model, and cool colors indicate higher estimates for the biological model. (D) No correlation between biological and biogeochemicl turnover estimates (log-log scale).