Assessing the potential fish and macroinvertebrate habitat provisioning services of kelp aquaculture in Southeast Alaska

BACKGROUND AND AIMS: Kelp aquaculture is a growing industry in Alaska where it has the potential to influence habitat provisioning for commercially and culturally important species. Given the seasonal presence of cultivated kelp mid-water, farms present a potentially novel habitat that could influence species' use of the nearshore zone. METHODS: Over one year, we surveyed two commercial farm sites paired with comparable non-farm control sites, assessing how the biotic assemblages and abiotic environment may be influenced by seasonal farm activities. We used environmental DNA to describe benthic and pelagic fish communities, and visual surveys on SCUBA to identify benthic macroinvertebrates and characterize the benthic environment. We also measured nutrient concentrations, temperature, and salinity. KEY RESULTS: Fish communities were structured significantly by season (30% of variation) and depth (7.9%) while macroinvertebrate communities were structured significantly by region (17.5%). Due to a missed sample event, the significance of the farm treatment could not be calculated, however the farm treatment 4.3% and 22.3% of variation in the fish and macroinvertebrate communities, respectively. The high effect size of both farm treatment and region in explaining macroinverterbate community variation suggests that communities may be spatially heterogeneous rather than specifically responding to the farm presence. Abiotic variables measured differed seasonally and by depth with no significant difference by farm treatment. CONCLUSIONS: Our findings suggest minimal influence of the kelp farms on the biotic communities or abiotic environments surveyed. We did not observe unique biotic assemblages in the kelp farm sites which would be indicative of farms providing novel habitat provisioning services. At the farm size and location surveyed, kelp aquaculture did not appear to detract from the important habitat already present. Our results should aid regulators as they make decisions to support the sustainable growth of the industry.