Epstein, G. | Search bioRxiv

bioRxiv2022

Protecting seabed sediment carbon for climate mitigation: a UK case study

Protecting areas of seabed sediment would appear to be an important climate mitigation strategy, however carbon has not been considered in national management plans. Using spatial analyses we show, in the UK Exclusive Economic Zone (EEZ), high potential organic carbon loss due to mobile bottom fishing is likely to be geographically restricted. Currently designated seabed marine protected areas (MPAs) cover 32.9% of the EEZ, 30.0% of carbon stocks, but only 12.9% of fishing disturbance. If all MPAs were closed to mobile bottom fishing, we estimate a prevention of only 6.9% of potential organic carbon losses due to fishing disturbance across the EEZ. In contrast, areas identified as having largest climate change mitigation potential cover just 16.5% of the EEZ, contain 24.7% of OC stocks and closing these areas to mobile fishing could save 29.6% of potential carbon losses. We must re-evaluate current seabed management plans and incorporate evidence-based carbon considerations. TeaserRestrictions on bottom trawling and dredging outside of MPA networks may be necessary to derive a climate mitigation benefit.

ecology↗

bioRxiv2021

The potential for mobile demersal fishing to reduce carbon storage and sequestration in seabed sediments

Subtidal marine sediments are one of the planets primary carbon stores and strongly influence the oceanic sink for atmospheric CO2. By far the most pervasive human activity occurring on the seabed is bottom trawling and dredging for fish and shellfish. A global first-order estimate suggested mobile demersal fishing activities may cause 160-400 Mt of organic carbon (OC) to be remineralised annually from seabed sediment carbon stores. There are, however, many uncertainties in this calculation. Here, we discuss the potential drivers of change in seabed OC stores due to mobile demersal fishing activities and conduct a systematic review, synthesising studies where this interaction has been directly investigated. Mobile demersal fishing would be expected to reduce OC in seabed stores, albeit with site-specific variability. Reductions would occur due to lower production of flora and fauna, the loss of fine flocculent material, increased sediment resuspension, mixing and transport, and increased oxygen exposure. This would be offset to some extent by reduced faunal bioturbation and respiration, increased off-shelf transport and increases in primary production from the resuspension of nutrients. Studies which directly investigated the impact of demersal fishing on OC stocks had mixed results. A finding of no significant effect was reported in 51% of 59 experimental contrasts; 41% reported lower OC due to fishing activities, with 8% reporting higher OC. In relation to remineralisation rates within the seabed, 14 experimental contrasts reported that demersal fishing activities decreased remineralisation, with four reporting higher remineralisation rates. The direction of effects was related to sediment type, impact duration, study design and local hydrography. More evidence is urgently needed to accurately quantify the impact of anthropogenic physical disturbance on seabed carbon in different environmental settings, and incorporate full evidence-based carbon considerations into global seabed management.

ecology↗