Selectively Breeding Seaweed

The seaweed farming industry has enjoyed rapid, robust growth over the past 15 years,1, 2 with cultivation emerging outside Asia in new regions like Europe and North America. Globally, seaweed farming has more than doubled its production over the past decade alone, and is currently the fastest-growing aquaculture sector, accounting for approximately 51% of aquaculture production.2

Cultivation of seaweed contributes to global food security, helps mitigate climate change, provides important ecosystem services, and offers significant socioeconomic benefits.3 Although 97% of harvested seaweed comes from farms,3 the wild seaweed in our oceans currently serves as the principal nursery for many of those farms.

Climate change impacts

Over the past few decades, climate change has directly impacted wild seaweed habitats throughout the world, resulting in their rapid decline, as well as significantly altered marine ecosystems.4 Rising ocean temperatures, reduced water quality, marine heat waves, invasive species, extreme weather events, and other climatic factors all contribute to losses in wild seaweed primary production and biodiversity.

Unfortunately, seaweed farms are also susceptible to these same climate change stressors. Production losses are largely due to disease, pests, and other environmental factors, which are increasingly exacerbated by climate change.2, 5, 6 Continuing climate impacts could significantly threaten seaweed production volumes in the coming years.

As seaweed becomes more important globally as a sustainable food source, a climate change mitigator, and a vital component of many countries’ economies, the imperiled status of the world’s wild seaweed populations is a primary concern for the seaweed farming industry. Because of climate change, as well as overharvesting in some areas, wild seed stock is a less reliable source—becoming increasingly unavailable and sometimes consisting of poorer quality.

Due to this dependence on wild sources of seed, the seaweed farming industry has an urgent need for seed stock. One viable solution is to use specialized culture and selective breeding techniques to produce highly productive, climate-resilient cultivars that seaweed farmers can plant in their farms. These same cultivars can also be invaluable tools for macroalgal reforestation efforts in replenishing wild seaweed habitats decimated by warming waters. Using local wild seed stock, researchers can grow cultivars native to a particular region and then outplant climate-resilient offspring that are better adapted to the changes in that local environment.7

Selective breeding

Although Charles Darwin first used the term selective breeding in 1859, cultures around the world have been using this process for centuries to grow fruits, vegetables, grains, and other plants with specific desired traits, such as a blight-resistant potato, faster-growing rice, or a crisper apple. Selective breeding has also been used throughout history to produce domesticated animals with particular traits, such as dogs with an instinct for herding sheep.

Selective breeding is not genetic modification, where scientists use invasive techniques to transfer genes from other species or to alter genes by manipulating DNA. Selective breeding is the deliberate pairing of a male and a female organism (the parents) to produce a particular type of offspring.

When selectively breeding seaweed, a scientist chooses parent plants from the wild population that they deem to have the desired traits—a sort of macroalgal matchmaking—and then pairs them to produce plants that, hopefully, also possess those particular traits. Then they repeat the process for each subsequent generation, selecting the parent plants that appear to have the best representation of the desired traits, which can eventually make those traits more dominant in the seaweed. When this same process occurs in the wild with random pairing and survival of the fittest, so that organisms change to adapt to their environments over many, many years, it’s known as natural selection, the basis for Darwin’s theory of evolution.

Selectively breeding seaweed is a well-established concept. Many Asian countries, such as China, Japan, and the Republic of Korea, have been using this method at their seaweed farms for decades.8, 9, 10, 11 And history shows that humans have been managing and domesticating seaweed since ~3000 BCE.12 Recognizing the need to develop national and regional aquaculture seed supply strategies and policies, in 2019, the Food and Agriculture Organization (FAO) of the United Nations created a global plan of action for aquatic genetic resources that focuses on selective breeding as one of its main priorities.3

Selective breeding is typically a methodical, gradual natural process that involves a great deal of painstaking trial and error. As they develop new cultivars, scientists must be careful to avoid extensive inbreeding, which can result in monocultures that become vulnerable to certain environmental stressors, such as disease and pests, due to a lack of genetic diversity.6 Developing and maintaining a broad-based inventory of parental stock is critical in ensuring and protecting that diversity.

Research at Woods Hole Oceanographic Institution

To support selective breeding research for seaweed, WWF is funding an ongoing project at Woods Hole Oceanographic Institution (WHOI) to develop cultivars of sugar kelp, Saccharina latissima, that yield increased biomass and are more resistant to pests and higher temperatures. Sugar kelp is the predominant seaweed species grown in the US and in Europe, and is one of the most economically and ecologically significant kelps.8, 13 It is closely related to Saccharina japonica, the predominant kelp grown in the Asia Pacific region and the basis of a more than 10 billion USD industry.14, 15

During their research, WHOI scientists are concurrently developing tools to make the entire selective breeding process more efficient and expedient, and more effective and productive in its outcomes. Their research program has produced baseline population genetic information for sugar kelp in the Gulf of Maine and southern New England areas of the US, as well as extensive genotyping and phenotyping data, which they are using to create genomic prediction models.16 With these tools, the WHOI scientists, and others, are able to estimate the breeding value of individual parents and predict the performance of their offspring regarding harvest yield, composition, and temperature tolerance.16 Over the past five years, more than 1000 unique crosses have been farm-tested, and more than 20 crosses produced twice the yield of average farm yields in the Gulf of Maine.16

The WHOI research team has also sequenced the genome of 500 of the approximately 1000 parents they have collected from New England. This collection forms the basis of a publicly available germplasm library at the National Center for Marine Algae and Microbiota (, helping to preserve genetic diversity for future uses and generations.17 This type of germplasm (gametophytes) enables nurseries to 1) obtain seed stock without impacting wild sources, 2) start the nursery and growing season earlier, and 3) produce consistent, reliable, high-quality harvests. Additionally, with assistance from the University of Southern California, WHOI is exploring the development of nonreproductive cultivars to address the concern that interbreeding between farmed and wild seaweed could eventually alter the genetic diversity and resiliency of wild seaweed.18

This important research at WHOI supports global efforts to develop climate-smart, resilient, and productive cultivars for the seaweed industry, and to provide potential solutions for revitalizing and protecting wild seaweed populations. Both of these goals help ensure that seaweed farming continues to grow and develop as a vital sustainable and restorative aquaculture industry. Selective breeding provides opportunities for the seaweed industry to scale significantly, which in turn increases its impact as a climate change mitigator and ecosystem services provider. Additionally, more productive yields can help make the industry more economically viable, ensuring a robust future that is able to adapt to ongoing climate challenges.

Key knowledge gaps remain in fully understanding the complex interactions of the environment, microbes, and genetics of seaweeds. Resolving these interactions will accelerate research, conservation, and practical applications. We need to continue developing advanced tools and optimized methods to overcome the current challenges in macroalgal cultivation, and to ensure the critical longevity of our wild seaweed habitats.


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