Kelp Farming as a Potential Strategy for Remediating Ocean Acidification and Improving Shellfish Cultivation

Nichole Price1, Suzanne Arnold2, Paul Dobbins3, Brittney Honisch4, Christopher W Hunt5, Melissa Melendez6, Matthew Moretti7, Joseph Salisbury II5 and Shawn Shellito8, (1)Bigelow Laboratory for Ocean Sciences, East Boothbay, ME, United States, (2)Island Institute, Rockland, ME, United States, (3)World Wildlife Fund, Washington, United States, (4)Bigelow Lab for Ocean Sciences, East Boothbay, ME, United States, (5)University of New Hampshire, Durham, NH, United States, (6)University of New Hampshire, Earth Sciences, Durham, NH, United States, (7)Bangs Island Mussels, Portland, United States, (8)University of New Hampshire Main Campus, Durham, United States
It has been proposed that the carbon capturing role of growing and harvesting macroalgae can be harnessed to locally remediate ocean and coastal acidification (OCA). Cultivated macroalgae may remove sufficient amounts of CO2 via primary production to mitigate OCA at small spatial scales, creating a ‘halo’ of improved water quality. Our study investigated the spatiotemporal patterns of this halo effect and possible enhancement of shellfish production at the Ocean Approved seaweed farm growing sugar kelp (Saccharina latissima) in Casco Bay, Maine. For three growing seasons, a moored array of instruments deployed inside and outside of the kelp farm measured flow, salinity, temperature, dissolved oxygen, pH, and pCO2. During peak kelp productivity, pCO2 was lower inside the farm, and as a result, pH was 13% higher and Ω was 23% higher. To determine the spatial extent of the halo, multiple cruises on a vessel equipped with flow-through sensors operating underway were used to georeference biogeochemical conditions at high resolution across a growing season. Although the ‘halo’ effect was detectable, the magnitude was inconsistent over time and space and was likely impacted by myriad biological and physical factors. Lab assays verified that flow and irradiance interact to determine kelp carbon capture potential and relative changes to the carbonate system downstream. To discern if the measured halo improved mussel fitness, year-old mussel lines were deployed inside predator exclusion cages at increasing distances from the farm (0, 125, 180, 395m) for two months just before kelp harvest. Mussels (Mytilus edulis) grown within the kelp farm had shells with significantly greater acute pressure resistance (75%), higher force tolerances to breakage (5%), greater shell thickness (27%) and density (88%), and larger meat masses (28%). This study provides evidence that co-cultivation can provide a strategy for reducing marine calcifier stress and increasing mussel product quality.