Persistence of Biogeochemical Alterations of Deep‐Sea Sediments by Bottom Trawling

Abstract

Continental margins are the continuum between the land and the ocean, and they are responsible for the majority of both burial and remineralization of organic carbon (OC) in the ocean (Dunne et al., 2007). However, biogeochemical cycles of organic matter in continental margins are altered by several anthropogenic activities (Bauer et al., 2013). Amongst those, bottom trawling is considered to be the most harmful and has the potential to alter the biogeochemistry of continental margins at a global scale given its widespread extension, high frequency, and direct impacts on the seafloor (

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

“…The results of recent regional and global scale publications which calculated first-order estimates of CO 2 produced from disturbance to seabed sediments by mobile demersal fishing must be taken with both concern and caution (Luisetti et al 2019, Paradis et al 2021, Sala et al 2021). As identified in this review, demersal fishing by trawling and dredging is in many cases likely to limit the storage and sequestration of OC, but to draw firm conclusions more experimental studies covering a wide range of environmental settings, habitat types and fishing pressures is required to address the large number of unknowns and site-specific drivers associated with the status of OC on the seabed.…”

“…Further, due to their often biological origin, fine grained sediments such as silts and clays typically have higher concentrations of OC compared to habitats dominated by sand and coarse sediment (Burdige 2007, Paradis et al 2021, Smeaton et al 2021). As mobile demersal fishing generally exposes or suspends fine material, this would tend to reduce overall OC storage through resuspension, oxidation and remineralisation (Fig.…”

“…Recent first order estimates have suggested that globally, mobile demersal fishing could remineralise between 160 - 400 Mt of OC from marine sediment stores annually (Sala et al 2021). It has also been suggested that historical trawling on global continental slopes could have removed ~6000 Mt of OC from the upper-most centimetre of sediment alone (Paradis et al 2021). In addition, it has been estimated that ~2 Mt of OC is remineralised from UK shelf sediments each year by mobile demersal fishing (Luisetti et al 2019).…”

“…In this review we discuss the potential drivers of change in sediment OC due to mobile demersal fishing activities, and summarise empirical evidence where their effects on sediment OC has been investigated. We also discuss recent peer reviewed publications which aim to quantify the impact of mobile demersal fishing at global, regional and national scales, and highlight why the results must be viewed with both concern and caution (Luisetti et al 2019, Paradis et al 2021, Sala et al 2021). If seabed sediments were to be recognised as a quantifiable and manageable blue carbon resource it could unlock huge climate change mitigation potential and carbon financing opportunities (Avelar et al 2017, Seddon et al 2019).…”

Biogeochemical consequences of a changing Arctic shelf seafloor ecosystem

“…Atlantic cod Gadus morhua , Greenland halibut Reinhardtuis hippoglossoides , shrimp Pandalus borealis ), commercial fisheries follow and start trawling some of the last unfished areas of the global shelf seafloor. Bottom trawling causes re-working and re-suspension of seafloor sediment (Puig et al 2012 ; O’Neill and Ivanović 2016 ), which can lead to erosion and perturbations to benthic biogeochemistry, in particular a loss of sedimentary organic carbon (Paradis et al 2021 ). However, in the Barents Sea, reactive OM is quickly degraded and recycled to CO 2 within the surface sediments (Freitas et al 2020 ; Stevenson et al 2020 ), even without human intervention.…”