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Integrated offshore cultivation of high value seaweed and their potential use in controlling harmful algal blooms.

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The benefits of seaweed cultivation

Seaweed has many uses such as reducing the impact of toxic microalgae on farmed bivalves and cleaning surrounding waters. One project has looked into effective cultivation processes.

Food and Natural Resources icon Food and Natural Resources

Seaweed has been used for centuries in traditional medicine and food. Now, seaweed and seaweed extracts are to be found in a wide range of products including food, food additives, animal feeds, pharmaceuticals, cosmetics, fertilisers, plant biostimulants, biomaterials and biofuels. Between 2000 and 2018, global seaweed production increased over threefold, from 10.6 to 32.4 million tonnes, and has an estimated value of EUR 11 billion. While growth in seaweed production in South-East Asia has slowed in the last few years, seaweed farming in other parts of the world continues to rise. Europe is eyeing this environmentally sustainable marine product with interest. The EU’s IntegraSea project focused on how cultivated seaweed can be used to mitigate eutrophication, along with harmful microalgal blooms, known as HABs. “In aquaculture, the fish waste nutrients can be detrimental for the surrounding environment and also for the cultivated fish. One way to address this issue is by cultivating seaweed that will use these waste nutrients to build their biomass, effectively removing it from the water,” explains Raquel Quintã, Marie Skłodowska-Curie research fellow at the Portuguese Institute for Sea and Atmosphere (IPMA) in Lisbon, Portugal.

Allelopathy and bioremediation in one

Allelopathy refers to the chemical inhibition of one organism by another, due to the release into the environment of substances acting as growth inhibitors. IntegraSea investigated the allelopathic potential of several seaweed species as a growth inhibitor of a toxic microalgae. The project developed and optimised hatchery techniques for several local seaweed species that, although not yet cultivated, have sound commercial potential. Their uptake of by-products also means the seaweed keeps the surrounding waters clean, leading to effective and natural bioremediation. Conducting the offshore part of their trials in Olhão, at the pilot aquaculture production area in collaboration with Armona Fish Farms, IntegraSea managed to obtain seeded strings in the hatchery and transferred them to grow-out systems. “Offshore and land-based ‘grow-out’ trials are seeking to find the best methods for these species’ cultivation, with special attention on overcoming known bottlenecks related to the local oceanographic and environmental conditions,” notes Quintã. She adds that work on selected seaweed bioremediation and allelopathic potential in connection with toxic microalgae showed promising results.

Cost-effective, cleaner aquaculture

“With the potential to reduce waste nutrients and downtime caused by high toxicity levels in bivalves that are due to be harvested, IntegraSea may have a natural solution to a recurring problem,” Quintã explains. The project demonstrated that when it comes to the integration of organisms of different trophic levels in the same aquaculture system, known as IMTA, algae cultivation can play a key role. As Quintã points out, research into new, local species and a better understanding of the diverse conditions in which the farmers operate gives growers the know-how to embrace an effective solution that has no negative impact on the waters. To bring this closer to a viable market option, one of the crucial next steps the team has identified will be to investigate if this observed effect can be exploited in a pilot project at scale. “Using seaweed is an exciting prospect since aquaculture is set to grow as an industry and if we can find a way to clean stocks sustainably, that will be a real breakthrough!” says Quintã.

Keywords

IntegraSea, seaweed, bioremediation, IMTA, Harmful microAlgal Blooms, HABs, allelopathy, aquaculture

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