Estimating sensitivity of seabed habitats to disturbance by bottom trawling based on the longevity of benthic fauna

Abstract

Bottom fishing such as trawling and dredging may pose serious risks to the seabed and benthic habitats, calling for a quantitative assessment method to evaluate the impact and guide management to develop mitigation measures. We provide a method to estimate the sensitivity of benthic habitats based on the longevity composition of the invertebrate community. We hypothesize that long‐lived species are more sensitive to trawling mortality due to their lower pace of life (i.e., slower growth, late maturation). We analyze data from box‐core and grab samples taken from 401 stations in the English Channel and southern North Sea to estimate the habitat‐specific longevity composition of the benthic invertebrate community and of specific functional groups (i.e., suspension feeders and bioturbators), and examine how bottom trawling affects the longevity biomass composition. The longevity biomass composition differed between habitats governed by differences in sediment composition (gravel and mud content) and tidal bed‐shear stress. The biomass proportion of long‐lived species increased with gravel content and decreased with mud content and shear stress. Bioturbators had a higher median longevity than suspension feeders. Trawling, in particular by gears that penetrate the seabed >2 cm, shifted the community toward shorter‐lived species. Changes from bottom trawling were highest in habitats with many long‐lived species (hence increasing with gravel content, decreasing with mud content). Benthic communities in high shear stress habitats were less affected by bottom trawling. Using these relationships, we predicted the sensitivity of the benthic community from bottom trawling impact at large spatial scale (the North Sea). We derived different benthic sensitivity metrics that provide a basis to estimate indicators of trawling impact on a continuous scale for the total community and specific functional groups. In combination with high resolution data of trawling pressure, our approach can be used to monitor and assess trawling impact and seabed status at the scale of the region or broadscale habitat and to compare the environmental impact of bottom‐contacting fishing gears across fisheries.

Recent advances in understanding the environmental footprint of trawling on the seabed

“…A further extension of this research has shown that taxon longevity predicts recovery rate (Rijnsdorp et al 2018;Hiddink et al 2019). The latter finding concurs with expectations based on our understanding of the likely response of long-lived species.…”

Assessing bottom trawling impacts based on the longevity of benthic invertebrates

“…This fraction is habitat‐specific and was derived by Rijnsdorp et al. () from the cumulative biomass distribution of infaunal invertebrates by T max category in the North Sea, as determined from grab and box core samples in untrawled locations (the effects of not including epifauna in these estimates is not known). Because we express category‐specific K as a fraction,over T max categories j (although the approach could be based on absolute estimates of category‐specific K if they were available).…”

Spatio‐temporal dynamics of multi‐trophic communities reveal ecosystem‐wide functional reorganization

“…morphological, demographic or physiological attributes; Violle et al 2007), rather than their taxonomic identity, determine their responses to the environment (Keddy 1992, Diaz et al 1998). For example, community traits of benthic invertebrates are often scrutinized to investigate the impacts of bottom trawling, with species characterized by long lifespan or epifaunal position being less abundant in highly disturbed communities (De Juan et al 2007, Rijnsdorp et al 2018. For example, community traits of benthic invertebrates are often scrutinized to investigate the impacts of bottom trawling, with species characterized by long lifespan or epifaunal position being less abundant in highly disturbed communities (De Juan et al 2007, Rijnsdorp et al 2018.…”

“…Hence, the use of traits provides a more mechanistic approach to understanding changes in community composition in comparison to more case-specific taxonomic information (McGill et al 2006, Shipley et al 2006. For example, community traits of benthic invertebrates are often scrutinized to investigate the impacts of bottom trawling, with species characterized by long lifespan or epifaunal position being less abundant in highly disturbed communities (De Juan et al 2007, Rijnsdorp et al 2018. Moreover, trait identity and diversity are linked to ecosystem functions (Diaz andCabido 2001, Gagic et al 2015) from which important ecosystem services can be derived, such as seafood and climate regulation.…”