Seaweed industry, including farming and sustainable wild harvesting, can offer nature-based solutions for climate and environmental change, thus minimizing threats to biodiversity and human welfare and therefore contributing to the United Nation Sustainable Development Goals. Seaweed farming is a multibillion-dollar industry and the fastest-growing aquaculture sector worldwide with high potential for scalability. However, little is known about the consequences, either positive or negative, of seaweed farming and wild harvesting in the surrounding natural ecosystems, and there is a complete lack of mechanistic understanding on the potential impacts of prospective large-scale seaweed farming. This session aims to bring together the current state-of-the-art research on environmental consequences of seaweed farming and harvesting, as well as discuss possible future trajectories of large-scale seaweed farming. This session welcomes research studies, industry and social initiatives, and policy strategies, from across the globe aiming at the assessment, management, and implementation of seaweed farming and harvesting from artisanal to industrial scales. Particularly, we welcome works on: 1) carbon capture by seaweed farms and overall contribution to carbon cycling including natural export pathways, induced sinking and its impacts 2) seaweed ocean acidification amelioration potential; 3) production of high-value molecules for industry replacing carbon intensive commodities and potential contribution to circular economy, global food security and livelihoods; 4) regenerative ocean farming, including seaweed and its effect in water quality through nutrient remediation and control of harmful algal blooms; 5) biodiversity enhancement by seaweed farms and effects in coastal areas; 6) observations or modeling studies that focus on seaweed cultivation as an ecological restoration tool for environmental and climate change impacts; 7) studies of Life Cycle Assessments to account for total GHG emissions in the seaweed industry and methodologies to verify carbon credits. ;
Lead Organizer: Glaucia Fragoso, NTNU (glaucia.m.fragoso@ntnu.no)
Co-organizers:
Ana Borrero, Seaweed Solutions (borrero@seaweedsolutions.com)
Aurora Ricart, Bigelow Laboratory for Ocean Sciences (aricart@bigelow.org)
Presentations
08:30 AM
Carrying capacity of the North Sea for seaweed cultivation – a modelling approach (5309)
Primary Presenter: Luca van Duren, DELTARES (luca.vanduren@deltares.nl)
While Saccharina latissima seaweed is currently cultivated in the Netherlands at a small scale, there is a major drive towards increasing sustainable offshore cultivation. Future wind farm areas are potential development locations. Harvesting seaweed leads to nutrient removal from the ecosystem. If this is done on a large scale, this can subsequently affect phytoplankton primary production, the basis of the marine food web. In this study, we investigate the spatial variability in ecosystem responses to seaweed cultivation in the Dutch North Sea in designated wind development areas. We focus on the interaction of seaweed and phytoplankton productivity with respect to nutrients and the effect of size, location and distribution of farms. We integrated a module simulating seaweed nutrient uptake and growth dynamics into a fully coupled 3D hydrodynamic-water quality model of the North Sea. We ran different cultivation scenarios over a production year and compared them to a run without seaweed cultivation. Results showed that significant upscaling of seaweed production (around 800 km2) in part of the designated areas for offshore wind development would have a strong impact on the ecology, with local decreases in spring phytoplankton production as high as 30%. Depending on locations, seaweed cultivation can also have a very large footprint in terms of impact on phytoplankton primary production. Models such as these benefit the societal debate about acceptable levels of upscaling.
08:45 AM
Carbon sequestration and creation of climate change refugia in seaweed farming (5443)
Primary Presenter: Aurora Ricart, Institut de Ciències del Mar & Bigelow Laboratory for Ocean Sciences (aricart@bigelow.org)
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.
09:00 AM
CHALLENGES AND BENEFITS OF AQUAFARMING SARGASSUM IN THE OPEN OCEAN COMBINED WITH ARTIFICIAL UPWELLING (6627)
Primary Presenter: Mar Fernandez Mendez, Alfred Wegener Institute (mar.fernandez-mendez@awi.de)
Aquafarming seaweed in the open ocean reduces pressure on coastal ecosystems, while creating new productive biodiverse habitats off-shore. Implementation poses huge engineering challenges and potential benefits. From all seaweeds, there is one that is particularly suited for open-ocean aquaculture. Holopelagic sargassum is a free-floating brown seaweed that rapidly divides by fragmentation, is very efficient at carbon uptake per unit of nutrient provided and creates a nursery habitat for diverse species. Its biomass is already converted into fossil-fuel replacing products (eg. fertilizers, emulsifiers and bioplastic). Aquafarming sargassum in nutrient replete areas will provide a stable feedstock for this nascent industry. To upscale production to the Gt scale, giant off-shore aquafarms can be created in the subtropical gyres. For fertilization, we investigated artificial upwelling of nutrient-rich deep water by harnessing salinity and temperature gradients. Our recent engineering advances on aquafarming barriers, model-based understanding of artificial upwelling pipes, and new discoveries on sargassums nutrient requirements, confirm the feasibility of sargassum aquafarming. Our study shows that combining artificial upwelling with seaweed aquafarming can alleviate some of the environmental impacts such as nutrient robbing. The formation of low oxygen areas in the deep sea, can be mitigated by processing and baling the biomass before sinking. Predicted environmental benefits include long-term carbon dioxide removal, enhanced open ocean biodiversity, and increased albedo.
09:15 AM
Home sweet home? Habitat provisioning by a UK sugar kelp farm (7342)
Primary Presenter: Sophie Corrigan, University of Exeter & The Marine Biological Association (sc718@exeter.ac.uk)
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.
09:30 AM
Modelling interactions between kelp cultures and the ocean carbon system (6974)
Primary Presenter: Ole Jacob Broch, SINTEF Ocean (ole.jacob.broch@sintef.no)
There is a surge of interest in how and to what extent macroalgal farming delivers positive ecosystem services and contributes to atmospheric CO2 sequestration. Recent results indicate that there may be significant positive contributions in both cases, but there is also due concern that there may be negative impacts of macroalgal farming at large extent and high intensities. We will highlight environmental and climate interactions of sugar kelp (Saccharina latissima) farming in Norway by using a high resolution coupled physics-biogeochemical-kelp ocean model system. The system takes into account two-way feedback between all its variables and includes forcing by atmospheric pCO2. Specifically, we will present simulation results on the interactions of the kelp cultures with the ocean carbon system. We will consider uptake of CO2 and production of O2 by the kelp cultures over the season and how this impacts on pH and alkalinity locally. We will also discuss new empirical results on vertical transport of particulate matter shredded from Saccharina latissima cultures, as well as the shredding rates, in the context of numerical modelling. The new results allow us to provide better estimates of the carbon export potential from Saccharina cultures. This research is funded by SINTEF's Climate fund (project Seaweed CDR) and the project "The Norwegian Continental Shelf: A Driver for Climate-Positive Norway" (NCS C+) funded by the Research Council of Norway (328715) under the green platform program.
09:45 AM
STANDARDIZED PROTOCOL FOR AN ENVIRONMENTAL RISK ASSESSMENT: A NEED FOR SEAWEED CULTIVATION. (6341)
Primary Presenter: Ana Borrero, Seaweed Solutions (borrero@seaweedsolutions.com)
Any activity either on land or in the ocean needs to identify and mitigate potential associated risks. That process is called environmental risk assessment (ERA). In Asia, seaweed cultivation is a well developing industry since the 1950’s. In Norway, the activity was mainly focused on research and pilot scale cultivation until the first commercial permission granted in 2014. in Norway a regulation for environmental risk assessment regarding seaweed cultivation has not been fully developed yet. Therefore, the industry lacks a standardized protocol for risk assessment. Methodology that has been developed by scientific communities partly require qualified personnel and are expensive. In this study, we propose cost effective methodology for farmers focusing on the topics proposed for the Norwegian regulations: i) genetic interactions between cultivated and wild seaweed, ii) spread of invasive species and diversity changes in ecological communities ecosystems, ii) epiphytes and diseases and iv) changes in the sediment.
SS027 Environmental Benefits and Risks of the Current and Future Seaweed Aquaculture Industry
Description
Time: 8:30 AM
Date: 7/6/2023
Room: Sala Portixol 1