Reviews and syntheses: Bioturbation impacts on sediment accretion and erosion in tidal marshes, with implications for carbon burial and sequestration

Abstract. Tidal marshes offer multiple ecosystem services, but are some of the most threatened coastal ecosystems worldwide. One of these valued services is their ability to sequester and store large amounts of carbon. Bioturbating macrofauna are ecosystem engineers that can influence the geomorphology and biogeochemistry of tidal marshes. Bioturbators can influence accretion and erosion processes in tidal marshes by either stabilizing or destabilizing sediment. Through this reworking of sediment, they can also influence the amount of carbon that can be stored. The impact of bioturbation on tidal marshes depend on a number of factors, such as, species composition, burrow morphology, diet, behaviour and habitat type. This review assesses the current knowledge on the role benthic bioturbators play in shaping sediment processes in tidal marshes and identifies key knowledge gaps for future research. For example, the impact of individual benthic species on sediment dynamics is mostly unknown. Bioturbation effects cannot be generalised and predicting when and where these effects will be most prominent is challenging. Future studies should investigate family and species specific effects on sediment properties, such as erodibility or texture, under controlled laboratory conditions and in the field. This should be compared across different habitat types such as ecotones, mudflats, salt marshes and mangroves. Furthermore, the role of consumers, as bioturbators, remains an understudied driver of the carbon cycle because it is complex. In order to better predict how tidal marshes may persist in the face of future climate change, such as sea level rise, it is important to understand the role of bioturbators on sediment and carbon dynamics to enable better mitigation of global change effects through conservation and restoration of tidal habitats.