For decades, the term “seaweed” has been used as a catch-all, but this collective term oversimplifies a remarkably diverse group of organisms. With over 12,000 species described, each with unique properties and applications, it’s clear that not all seaweeds are created equal. This recognition is at the heart of a burgeoning new field called phyconomy, which refers to the large-scale, sustainable cultivation of seaweeds for economic and industrial purposes.
The history of agriculture has shown us that to move from wild harvesting to advanced cultivation, we need to domesticate species and develop advanced agronomy practices. The seaweed industry is now at a similar crossroads. As the demand for specific types of seaweed biomass increases, and as challenges like climate change, disease, and unsustainable harvesting practices impact natural populations, the industry is turning to cultivation and innovative solutions to ensure a steady, high-quality supply.
This is where a game-changing concept comes into play: using seaweed extracts as biostimulants to enhance the cultivation of other seaweeds. This idea, though seemingly counterintuitive, is proving to be a powerful tool for building a more resilient and productive seaweed aquaculture industry.
The Power of Biostimulants: From Land to Sea
Seaweed extracts have long been a popular input in terrestrial agriculture, where they are used as biostimulants to promote plant growth, improve root development, and increase resistance to abiotic stressors like drought, salinity, and pests. They contain a plethora of organic and inorganic substances, including natural growth hormones, vitamins, and amino acids, that stimulate a plant’s natural processes without acting as traditional fertilizers.
The question now is whether these same principles can be applied to seaweed cultivation itself. The “Seaweed Extracts for Enhanced Cultivation of Seaweeds” (SEECS) project was established to explore this very idea. The core hypothesis is that an extract from one type of seaweed could be used to benefit the growth and health of another, even if the two species are evolutionarily unrelated.
Much of the foundational research has focused on the use of an extract from the cold-water brown seaweed, Ascophyllum nodosum (AMPEP), on the tropical red seaweed, Kappaphycus alvarezii, a major source of carrageenan for the global food and pharmaceutical industries.
A Proven Solution: How Seaweed Extracts Improve Cultivation
The research on the application of biostimulants to seaweed cultivation is yielding promising results across several key areas:
- Micropropagation and Nursery Stages: The earliest stages of cultivation, where seedlings are grown in a lab or nursery, are critical for ensuring a healthy, vigorous crop. Studies have shown that dipping young propagules of K. alvarezii in AMPEP before out-planting them into the sea results in higher daily growth rates and a more robust, disease-free crop.
- Mitigating Biotic and Abiotic Stress: Just like land-based crops, seaweeds face numerous stressors. Abiotic stresses include high surface seawater temperatures, light, and UV levels, particularly for crops grown near the surface in shallow waters. Biotic stressors include bacterial and viral pathogens, as well as infestations from epiphytic and endophytic organisms that can lead to crop loss. AMPEP has been shown to improve the thermal tolerance of kelp species and mitigate diseases like “ice-ice” in Kappaphycus, which has led to dramatic financial losses for farmers.
- Enhancing Carrageenan Quality: A common concern among processors was that using biostimulants might decrease the quality of the final product. However, studies have demonstrated the opposite. AMPEP-treated Kappaphycus has been shown to produce significantly higher yields of semirefined carrageenan, with improved viscosity and gel strength that remain within industry standards. This observation is economically significant and warrants further investigation on a commercial scale.
A Deeper Look: The Unanswered Questions
While the positive effects of seaweed biostimulants are undeniable, the exact mechanisms are still largely unknown. The science is still in its early stages, and there are many unanswered questions that need to be addressed to unlock the full potential of this technology.
- Mode of Action:Â What are the specific biochemical pathways and physiological responses involved? The effects are not simply from nutrient delivery but are likely driven by complex, hormone-like signaling molecules called “phyco-elicitors”.
- The Marine Microbiome: Researchers are exploring the idea that seaweed extracts may act as marine prebiotics, positively influencing the microbial communities on the surface of the seaweeds. This microbial network may be the seaweed’s first line of defense against pathogens and damaging epiphytes. The extracts might even interrupt a process called quorum sensing, a form of chemical communication that bacteria use to coordinate their attack on a host.
- A “Super Prebiotic” Effect:Â Seaweed extracts appear to have a “super prebiotic” effect, promoting beneficial bacteria while simultaneously suppressing the activity of pathogens. This allows the host’s immune system to focus its energy on growth and reproduction rather than on defense activities.
- Chemical Complexity:Â Seaweed extracts are not a single compound but a complex “soup” of constituents. The active compounds may not even be present in the original seaweed but are created during the extraction process through chemical reactions. Further research is needed to understand and harness this chemical language for our benefit.
Integrated Multi-Trophic Aquaculture (IMTA): A Synergistic Approach
The use of biostimulants is just one piece of the puzzle. The future of sustainable seaweed cultivation lies in its integration with other systems. IMTA is a prime example of this, combining the fed aquaculture of fish or shrimp with the extractive aquaculture of seaweeds and shellfish.
The principle behind IMTA is simple: the byproducts of one species become the food or fertilizer for another, creating a closed-loop system. For example, a seaweed farm can be located near a fish farm to absorb excess nutrients from fish waste, mitigating pollution and enhancing water quality. This diversification also makes aquaculture more economically resilient, as farmers are not solely reliant on one species.
Research has shown that adding seaweed extracts to IMTA systems can further enhance growth and resilience. A study on Kappaphycus alvarezii seedlings grown in shrimp effluent, for example, found that adding AMPEP improved the seaweed’s growth and metabolic profile, increasing its antioxidant content and its ability to fight off disease.
Conclusion: Cultivating Our Future
The transition from wild harvesting to industrial-scale seaweed cultivation is a crucial step toward building a sustainable future. It’s a journey that requires not only technological advancements but also a shift in our understanding of these incredible marine organisms. The research on biostimulants is a testament to this, showing that the solutions to our most complex problems may be found in the most unexpected places.
The global seaweed industry is at a crossroads, facing a choice between continuing with unsustainable practices or embracing a new era of innovation. The path forward is clear: to invest in research, foster collaboration, and implement integrated, holistic systems that treat our oceans as living, interconnected ecosystems. By doing so, we can ensure a steady, high-quality supply of this invaluable resource while simultaneously protecting our planet and empowering coastal communities for generations to come. The future, it seems, is ready to be ocean-grown.
