The restoration potential of offshore mussel farming on degraded seabed habitat

Abstract

The United Kingdom's first large-scale, offshore, long-line mussel farm deployed its first ropes in 2013 in Lyme Bay, southwest United Kingdom, located in an area of seabed that was heavily degraded due to historic bottom-towed fishing. It was hypothesised that due to the artificial structures that accumulate mussels and exclude destructive fishing practices, the seabed could be restored. To assess the restoration potential of the farm and its ecosystem interactions over time, a multi-method, annual monitoring approach was undertaken. Here, we tested the effects of the farm trial stations on the seabed habitat, epifauna and demersal species over 5 years. Responses of % mussel cover, sessile and sedentary, and mobile taxa were measured using three video methods. Within 2 years of infrastructure deployment, mussel clumps and shells were detected below the headlines, increasing the structural complexity of the seabed.After 4 years, there was a significantly greater abundance of mobile taxa compared to the Controls that remained open to trawling. Commercial European lobster and edible crab were almost exclusively recorded within the farm. We discuss whether these findings can be considered a restoration of the seabed and how these data can be used to inform the future management of offshore mariculture globally.

The IUCN Global Standard for Nature-based Solutions™ as a tool for enhancing the sustainable development of marine aquaculture

“…While aquaculture provisional services are straightforward to value in monetary terms, others are more difficult to quantify and are typically under-valued, even though they are often badly impacted by aquaculture itself (Muir et al, 1999). Stronger or more robust methods of assessing the biodiversity gain of aquaculture are under development (Filgueira et al, 2015;Le Gouvello et al, 2017;Alleway et al, 2018; Aubin The criteria of the IUCN Global Standard for Nature-based Solutions™ et al, 2019;Custodio et al, 2019;Smaal et al, 2019;Weitzman, 2019;Theuerkauf et al, 2021;Bridger et al, 2022;le Gouvello et al, 2022). The level at which Criterion 3 is met by an aquaculture intervention would largely depend on the type, species, and farming practices that the aquaculture system involves.…”

“…Positive effects of aquaculture production on biodiversity are documented (Mascorda Cabre et al, 2021;Theuerkauf et al, 2021;Bridger et al, 2022). Aggregations of transient and resident fish and marine mammals are observed around open sea cage facilities (Dempster et al, 2006;IUCN, 2021).…”

“…Aggregations of transient and resident fish and marine mammals are observed around open sea cage facilities (Dempster et al, 2006;IUCN, 2021). Aquaculture offshore platforms could be assimilated by Other Effective area-based Conservation Measures (Le Gouvello et al, 2017;IUCN-WCP, 2019;Appiott et al, 2021) as demonstrated in a mussel farm in the UK (Bridger et al, 2022).…”

The aggregation effect of offshore mussel farming on pelagic fishes

“…A multi‐method, long‐term research study was initiated to monitor the effect of the United Kingdom's first large‐scale offshore long‐line mussel farm in 2013, including sampling the epibenthos (Bridger et al., 2022), infauna (Mascorda‐Cabre et al 2023), plankton, birds and mammals. The aims of this study are to assess the effects of mussel headlines on pelagic fishes over time, as well as to investigate if the age of cultured mussels is correlated with the number of rope epibiota species and the abundance of pelagic fishes.…”

Quantification of finfish assemblages associated with mussel and seaweed farms in southwest UK provides evidence of potential benefits to fisheries

“…Hence there is growing interest surrounding the potential for farms to act as 'restorative' or 'regenerative' forms of aquaculture in areas where fish populations have been depleted due to degradation of natural habitats (Alleway et al 2023). Shellfish and seaweed farming infrastructure may also restrict fishing activities in the immediate vicinity, which could benefit populations of fish and other organisms by excluding extractive activities such as bottom trawling, thereby acting as de facto 'no take zones' with potential spill-over benefits for fisheries in surrounding areas (Olsgard et al 2008, Johnson et al 2015, Wang et al 2015, Gentry et al 2020, Bridger et al 2022. Farms may, however, induce changes in natural fish assemblages by altering food availability and quality (Oakes & Pondella 2009), or by replacing, modifying or damaging pre-existing habitats in the area, such as kelp forests, seagrass meadows or other important coastal habitats (McKindsey et al 2011, Wood et al 2017, Campbell et al 2019, Kelly et al 2020, Theuerkauf et al 2021, United Nations Environment Programme 2023.…”