Development and Diversity of Epibiont Assemblages on Cultivated Sugar Kelp (Saccharina latissima) in Relation to Farming Schedules and Harvesting Techniques

Abstract

Seaweed farming in Europe is growing and may provide environmental benefits, including habitat provisioning, coastal protection, and bioremediation. Habitat provisioning by seaweed farms remains largely unquantified, with previous research focused primarily on the detrimental effects of epibionts, rather than their roles in ecological functioning and ecosystem service provision. We monitored the development and diversity of epibiont assemblages on cultivated sugar kelp (Saccharina latissima) at a farm in Cornwall, southwest UK, and compared the effects of different harvesting techniques on epibiont assemblage structure. Increases in epibiont abundance (PERMANOVA, F4,25 = 100.56, p < 0.001) and diversity (PERMANOVA, F4,25 = 27.25, p < 0.001) were found on cultivated kelps over and beyond the growing season, reaching an average abundance of >6000 individuals per kelp plant with a taxonomic richness of ~9 phyla per kelp by late summer (August). Assemblages were dominated by crustaceans (mainly amphipods), molluscs (principally bivalves) and bryozoans, which provide important ecological roles, despite reducing crop quality. Partial harvesting techniques maintained, or increased, epibiont abundance and diversity beyond the farming season; however, these kelp plants were significantly fouled and would not be commercially viable in most markets. This paper improves understanding of epibiont assemblage development at European kelp farms, which can inform sustainable, ecosystem-based approaches to aquaculture.

Home sweet home: Comparison of epibiont assemblages associated with cultivated and wild sugar kelp (Saccharina latissima), co-cultivated blue mussels (Mytilus edulis) and farm infrastructure

“…1). Porthallow Bay is exposed to wind and wave action from the east and southeast, but is sheltered from the predominant south-westerly winds and North Atlantic swells, with the 16 ha integrated farm site situated at approximately 500 m from the shore (Corrigan et al 2023). The farm uses a longline system with 200 m header lines anchored to the seabed and suspended 1-3 m below the surface, supporting either seaweed or mussel growth (Fig.…”

“…1). Collections in May represented 'harvest' assemblages and those in August were indicative of 'post-harvest' assemblages, if and when kelp biomass is not removed from the farm to assess whether epibiont assemblages would become more similar to wild populations with time (Corrigan et al 2023). In May 2021, 18 kelp plants were collected (by boat) from three independent droppers spread along one seaweed header line.…”

“…Once removed, plants were placed into separate labelled sealable bags. In August 2020, a total of 36 kelp plants were sampled in the same way (Corrigan et al 2023). Ten wild kelps from natural populations, comparable in size to the farmed kelps, were collected from each rocky reef site in May 2021 and August 2020 using SCUBA.…”

“…All kelp samples were processed as per Corrigan et al (2023), whereby plants were defrosted and rinsed through a 0.5 mm sieve to remove any mobile or loosely attached fauna (hereafter referred to as 'mobile' epibionts). Samples were then thoroughly examined for any remaining sedentary or sessile individuals and colonial taxa (e.g.…”

“…The differences in these ndings, and other recent understandings of how epibiont assemblages vary widely between cultivation sites, dependent on latitude and environmental factors such as temperature, ow regime and wave exposure (Boderskov et (Forbes et al 2022). For seaweed farming to provide valuable long-term habitat, innovations to maintain biodiversity beyond the harvest point are being trialled, including partial harvesting techniques (Corrigan et al 2023). Co-location with other marine industries, such as renewable energy, or longer-lived aquaculture species, such as bivalve shell sh, can also increase the longevity of habitat.…”