World Aquaculture Magazine - June 2021

30 JUNE 2021 • WORLD AQUACULTURE • WWW.WA S .ORG unlikely that we will ever be able to cultivate enough seaweeds to change the pH of an ocean; however, at the level of a coast, an embayment or the intake of a shellfish hatchery, it is possible to have a significant impact. • The IMTAmulti-crop diversification approach (growing fish, seaweeds and invertebrates) could be an economic risk mitigation and management option to address pending climate change and coastal acidification impacts, thereby increasing the resilience of the aquaculture sector. • Seaweed cultivation and IMTA systems could be associated with wind farms, in multiple use food and renewable energy parks for a reduced cumulative footprint by combining the two activities, which could bring more societal acceptance for both activities. • Shuve et al. (2009) and Barrington et al. (2010) showed that people participating in surveys had a better appreciation of aquaculture and supported its implementation when IMTAwas explained to them. The value of these important services to the environment and, consequently, society are never accounted for in budget sheets and business plans of seaweed farms and companies. People are generally surprised when we show them, for example, that the economic value of the nutrient bioremediation services provided by the world’s current seaweed aquaculture production (32.4 MMT) is between US$1.2-3.5 billion, which is about 26 percent of its present commercial value (US$13.3 billion) (Chopin and Tacon 2021). While people and governments focus on carbon (C) trading taxes, we think that developing the concept of nutrient trading credits (NTC), in particular for the recovery of nitrogen and phosphorus, is much more important. There is more money to be made with NTC (between US$ 1.1-3.4 billion for N and US$ 51.8 million for P) than with carbon trading credits (US$ 29.1 million). Recognition and implementation of NTCs would give a fair price to seaweed and extractive aquaculture. They could be used as financial and regulatory incentive tools to encourage single-species aquaculturists to contemplate innovative practices, such as IMTA, as a viable alternative to their current practices. Here we highlight a few forms of what we consider seaweed aquaculture “hype” and add recommendations to help reorient us towards its realities in 2021. RealityCheck#1: Seaweeds for biofuels. Seaweeds for biofuels have been touted several times over the last few years as one of the promising materials for the fourth- generation biofuel reincarnation after three previous efforts did not take off (food crops, feedstock, microalgae). We have still not seen a commercial drop of seaweed biofuels. A reality check is necessary at several levels. It is doubtful that the surface area needed to secure the rawmaterials for significant biofuel production will be societally acceptable, especially in aquaculture’s new geographies. Seaweed biomass production is highly seasonal while people refill at fuel stations year round. How, then, do we store a product that is highly seasonal and in which form(s)? Scaling up from laboratory experiments and pilot farms to commercial markets needs a reality check. Moreover, to be economically competitive, seaweed biofuels would have to be economically competitive with fossil biofuels used now. Why try to sell seaweeds at several cents/MT fresh weight? The best way to move forward is to explore products from seaweeds that command much higher prices (Chopin and Tacon 2021). For our societies and for the good of our Earth, humans would be better off further developing seaweed applications with increased added value (up to more than US$ 1,000/kg dry weight), such as: • displacing chemical fertilizers with natural fertilizers like seaweeds, produced with a much smaller carbon footprint; • participating in the decarbonization of this world through a dietary shift towards the consumption of sustainable, safe, equitable, resilient and low-carbon ocean-based sources of foods and the mitigation of food insecurity while reducing gas emissions and carbon footprints from animal land-based food production systems (Hoegh-Guldberg et al . 2019); and • developing nutraceuticals and pharmaceuticals to prevent and treat neurodegenerative diseases such as Parkinson disease (Giffin et al. 2017), a terrible burden to societies and health care systems. RealityCheck#2: Seaweeds to reducemethane emissions fromcattle. The first paper on this topic attracted a lot of attention (Kinley et al. 2016). The rates of methane reduction were impressive but these experiments were conducted in vitro (i.e., in artificial rumens) not in vivo . There was no real cow absorbing one gram of the red seaweed Asparagopsis taxiformis . We are now reading papers with experiments conducted with real cows and the results are not as rosy as with the artificial rumens. Bromoform, a halogenated compound that reduces enteric methane emissions in cows, has been found to attack the walls of cow stomachs and residues have been found in cowmilk (Muizelaar et al. 2021). There are two other issues. First, A. taxiformis (and A. armata ) are small red seaweeds, not ubiquitous, and have complex life histories. Consequently, they can be produced with great care in academic and small-scale laboratory settings, but they will not be easy to produce at the large biomass levels necessary to feed a global cattle population estimated at about 1 billion head in 2020 (Statistica 2021). We recommend enlarging the screening to check if other seaweeds, able to be cultivated more easily in significant amounts, contain antimethanogenic compounds. For example, this is being done at the KTH Royal Institute of Technology in Stockholm, Sweden (Fredrik Gröndahl, personal communication). Second, how easy and realistic will it be to administer a daily dose of Asparagopsis to all of these cattle? Around 60 percent of the world’s cattle are not in feedlots but ranched in free-range pastures where they are encountered infrequently, mainly when counted or branded. Even in countries where feedlots are common, cattle normally remain in a feedlot for only 3-5 months of their 36-month average production cycle. Our opinion is that the science on using seaweeds to reduce methane emissions from cattle remains questionable. We recommend applying to this work a more rigorous use of one of the two overarching, ethical concepts of ecological aquaculture (Costa- Pierce 2021) — the Precautionary Principle. RealityCheck#3: Sinking seaweeds for carbon sequestration to the oceanbottom. Sinking seaweeds to the deep ocean floor for carbon sequestration can, at first, look like an attractive idea. However, it