Seaweed farms are expanding rapidly in Europe in response to increasing demand for seaweed-derived products. Seaweed farming may offer additional ecosystem services, such as habitat provisioning and elevated local biodiversity, which could benefit other marine industries including fisheries by providing breeding or feeding grounds to fish species. Few studies have substantiated these claims however, and it remains uncertain whether seaweed farms will support similar biodiversity to kelp forests or provide valuable long-term habitat beyond the harvest season. We surveyed integrated sugar kelp (Saccharina latissima) and blue mussel (Mytilus edulis) farms in southwest UK to compare epibiont and fish assemblages between cultivated kelps, mussel aquaculture and wild kelps or control sites. We found significant increases in epibiont abundance and diversity on farmed kelps over and beyond their growing season, reaching over 6000 individuals and 9 taxa present per kelp by late season. We found farmed kelps supported 16 times the abundance of epibionts living on wild kelps at harvest time, however, taxonomic diversity per kelp was lower at the farm. Farmed kelp assemblages were dominated by amphipods, which were present on the wild kelps but in much lower numbers. Farmed kelp also supported distinct assemblages to cultivated mussels, which hosted higher relative abundances of crabs, echinoderms, worms and red algal biomass. We found higher abundances of fish at the farm site compared to control areas, several of which are of commercial importance including pollock (Pollachius pollachius) and mackerel (Scomber scombrus). These results indicate that seaweed farms may provide new habitats for epibiont and fish species, however they are not analogous to natural kelp forests. Increased understanding of the potential habitat value of seaweed farms could help to inform the development of the seaweed farming industry in new areas such as Europe as a sustainable ecosystem-based approach to aquaculture.

Primary Presenter: Sophie Corrigan, University of Exeter & The Marine Biological Association (sc718@exeter.ac.uk)

Authors:

Charles Tyler,  University of Exeter  ()

A. Ross Brown, University of Exeter  ()

Ian Ashton, University of Exeter  ()

Catherine Wilding, Marine Biological Association   ()

Carly Daniels, University of Exeter  ()

Dan Smale, Marine Biological Association   ()