Seaweed farming has the potential to sequester CO₂ and locally provide acidification refugia. However, empirical evidence is largely lacking as many nearshore biogeochemical processes influence the concentration of CO₂ in seawater, complicating our understanding of the potential role of seaweed farms.  Here we present results from a sugar kelp (Saccharina latissima) farm in Casco Bay, Maine, USA. During three farming seasons, we collected high-frequency carbonate chemistry data -seawater temperature, salinity pH, pCO₂ and dissolved oxygen (DO) - inside, outside and around the farm to understand what the acidification amelioration potential is, how it occurs, when and to which extent. We also assessed air-sea CO₂ fluxes and net community production to understand the farm capacity to capture atmospheric CO₂, and the physiological effects of seawater carbonate chemistry changes on a blue mussel (Mytilus edulis).  The seaweed farm increased average pH, DO and decreased pCO₂, although there was significant spatiotemporal variability in the effect sizes. Both mixing and biology appear as the main drivers of the differences in dissolved inorganic carbon observed between inside and outside the farm, where biology tended to decrease it. Air-sea CO₂ fluxes showed that the seaweed farm was a carbon sink along the three farming seasons and net community production was particularly high inside the seaweed farm in spring and early summer, coinciding with the peak of high productivity of the seaweed species. Mussels growing inside the  farm for two months developed thicker shells than those grown outside. These results show the potential of seaweed farms as climate change mitigation strategies.  

Primary Presenter: Aurora Ricart, Institut de Ciències del Mar & Bigelow Laboratory for Ocean Sciences (aricart@bigelow.org)

Authors:

Aurora Ricart, Institut de Ciències del Mar (ICM-CSIC)  (aricart@bigelow.org)

Melissa Meléndez, University of Hawaii  (mmelen@hawaii.edu)

Brittney Honisch, Bigelow Laboratory for Ocean Sciences  (bhonisch@bigelow.org)

Nicholas Record, Bigelow Laboratory for Ocean Sciences  (nrecord@bigelow.org)

Christopher Hunt, University of New Hampshire  (chunt@unh.edu)

Joseph Salisbury, University of New Hampshire  (Joe.Salisbury@unh.edu)

Suzanne Arnold, Island Institute  (sarnold@islandinstitute.org)

Nichole Price, Bigelow Laboratory for Ocean Sciences  (nprice@bigelow.org)