Offshore longline mussel farms: a review of oceanographic and ecological interactions to inform future research needs, policy and management

Abstract

With a growing human population and the need to protect our oceans from overfishing, there is a requirement for society to source alternative means of sustainable protein. Mussel aquaculture has rapidly expanded in many countries serving as an important supply of protein, but its development has been limited due to competition for coastal space and the associated environmental impacts of farming in inshore waters. Offshore aquaculture developments have the potential to overcome such issues. This review synthesises the current literature on the ecological and oceanographic interactions of longline offshore mussel farms with the aim to elucidate the main knowledge gaps in a context of management and conservation. Large offshore aquaculture installations interact with the hydrodynamics of the area causing water flow distortions and current attenuation, wake formation and distorting water column stratification which can have an effect on the supply of nutrient and seston as well as altering material dispersal, biodeposition and resuspension, having in turn, a knock-on effect on the carrying capacity of the system, ultimately affecting the surrounding ecology and its ecosystem services. Offshore mussel farm studies report an increase biomass or numbers of benthic and pelagic organisms beneath and around mussel ropes relative to control sites using the structure for shelter, refuge and nursery. Improving our understanding of offshore aquaculture-environment interactions is crucial to identify the priorities needed for future research to inform policy and management practices as well as its role as part of the Blue Growth Agenda and as 'other effective area-based conservation measures' (OECMs).

Mussel biology: from the byssus to ecology and physiology, including microplastic ingestion and deep-sea adaptations

“…Mussels of the genera Mytilus and Perna (Fig. 1), distributed from temperate to polar and subtropical to tropical marine zones, respectively, are popular as food and are actively cultured (Gosling 1992;Maquirang et al 2020;Cabre et al 2021). In addition, mussels are distributed in freshwater and even in deep seas (Fig.…”

Circular and lower impact mussel and seaweed aquaculture by a shift towards bio‐based ropes

“…Mussel and seaweed are cultured in ropes suspended mainly from raft and longline systems made of non‐biodegradable fossil‐based plastics 18 . The expansion of mussel and seaweed productions, including IMTA, would correspondingly increase the rope demand and use in marine environments.…”

“…Mussel and seaweed are cultured in ropes suspended mainly from raft and longline systems made of non-biodegradable fossil-based plastics. 18 The expansion of mussel and seaweed productions, including IMTA, would correspondingly increase the rope demand and use in marine environments. Heavy weather conditions, mismanagement of gears in aquaculture productions, the inadequate waste collection facilities at harbours and subsequent management possibilities, may result in plastic waste and marine litter generation.…”

Mussel farming production capacity and food web interactions in a mesotrophic environment

“…Mussel production in the European Union has decreased over the last 2 decades; causes of the decline are presumed to be environmental factors, including available space, rather than economic factors (Avdelas et al 2021). Conflicting activities and environmental pressure on coastal waters demand the consideration of other areas and ecosystems for LTA production, and an increasing interest in expansion to offshore sites and less exposed or unexploited coastal regions like meso-oligotrophic fjord areas has arisen (Strohmeier et al 2009, Torrissen et al 2018, Galparsoro et al 2020, Mascorda Cabre et al 2021, Thomas et al 2022. Remote sites, lack of infrastructure and insufficient conditions for culture may restrict such areas from being exploited.…”