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).

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.

No abstract