Seaweed, a diverse group of marine algae, thrives in oceans worldwide, anchoring itself to solid structures or floating in vast underwater meadows. These fascinating organisms, ranging from microscopic forms to giant kelp forests, are macroscopic, multicellular algae found in various colors, including red, brown, and green. Often seen washed ashore, seaweed is a natural component of marine ecosystems. Beyond its presence in coastal environments, seaweed offers substantial advantages for the planet. Its unique biological processes and various applications contribute significantly to environmental well-being.
Seaweed’s Role in Carbon Absorption
Seaweed plays a substantial role in mitigating climate change by absorbing large amounts of carbon dioxide (CO2) from the atmosphere and oceans. Through photosynthesis, similar to land plants, seaweed converts CO2 into organic compounds for growth. This process makes marine algae highly efficient at capturing carbon, with kelp forests, for example, absorbing up to 4.5 to 5 million tons of CO2 annually.
The carbon captured by seaweed ecosystems is often referred to as “blue carbon” when stored in coastal and marine environments. Seaweed forests, especially kelp, are particularly effective carbon sinks, potentially absorbing carbon at a faster rate than terrestrial forests. This absorbed carbon can be stored long-term in ocean sediments when seaweed detritus sinks to the seafloor, contributing to natural carbon sequestration.
Globally, seaweed is estimated to sequester nearly 200 million tonnes of carbon dioxide every year. Expanding sustainable seaweed farming to 13.39–25.14 million hectares by 2050 could sequester an additional 2.50–4.72 gigatons of carbon dioxide. This natural carbon uptake helps reduce atmospheric CO2 levels and lessens ocean acidification, a consequence of rising CO2 absorption by oceans.
Enhancing Marine Ecosystems
Seaweed ecosystems contribute to the health and biodiversity of marine environments. They form extensive underwater “forests,” particularly kelp, which provide shelter, food, and breeding grounds for marine species. These dense growths create complex habitats, supporting diverse fish, invertebrates, and microorganisms, thereby increasing the abundance of marine life.
Beyond providing physical habitat, seaweed improves water quality by filtering excess nutrients and pollutants. It absorbs substances like nitrogen and phosphorus, which can originate from agricultural runoff and sewage discharge. This biofiltration process helps reduce the risk of harmful algal blooms and improves water clarity.
Seaweed also plays a role in mitigating ocean acidification locally. Through photosynthesis, seaweed removes dissolved CO2 from the water, which can help buffer pH changes in the surrounding environment. This benefits marine organisms, such as shellfish, sensitive to acidic waters. Additionally, the large size and dense structure of seaweed, particularly kelp, can attenuate wave energy, helping to protect coastlines from erosion.
Sustainable Uses and Products
Seaweed offers sustainable applications across industries. As a food source, seaweed is low-impact, requiring no fresh water, land, or fertilizers for cultivation, making it a sustainable and nutrient-rich option. For example, edible seaweeds like nori and kombu are consumed globally and are rich in vitamins and minerals.
In agriculture, seaweed can be processed into biofertilizers, providing a natural alternative to synthetic chemical fertilizers and reducing agricultural runoff into waterways. These fertilizers enhance soil fertility, improve water retention, and strengthen plant immunity against stressors. Additionally, seaweed is being explored as an animal feed additive, particularly for livestock, where certain varieties, like Asparagopsis, have shown promise in reducing methane emissions by up to 97% by inhibiting specific enzymes in the digestive system.
Seaweed also holds potential for developing biodegradable materials, such as bioplastics and packaging, offering alternatives to fossil-fuel-derived plastics. These seaweed-based bioplastics are often derived from brown seaweed and are malleable, biodegradable, and hydrophilic, suitable for items like food wrappers and cutlery. It is also a source for biofuel production, a renewable energy option that does not compete for land or freshwater. These applications highlight seaweed’s versatility in fostering a more sustainable economy.
Responsible Cultivation Practices
While seaweed offers environmental benefits, responsible cultivation practices are important to maximize its positive impact and minimize any localized adverse effects. Careful site selection is necessary to avoid sensitive marine habitats, such as seagrass beds and coral reefs, and ensure that farms do not interfere with existing ecosystems or navigation routes. This maintains coastal ecological balance.
Selecting native seaweed species for cultivation prevents ecological disruption. Introducing non-native species could potentially outcompete local flora or introduce diseases, altering the natural biodiversity of an area. Sustainable harvesting methods are implemented to ensure the regeneration of seaweed populations and avoid over-harvesting, which could deplete natural stocks. Harvesters often cut fronds above the growth point, leaving holdfasts intact, and rotate harvesting areas to allow for recovery.
Continuous monitoring and research are also conducted to understand the long-term environmental impacts of large-scale seaweed aquaculture. This includes changes in light penetration, nutrient levels, and potential entanglement risks for marine mammals. This ongoing evaluation helps optimize cultivation techniques, ensuring they remain beneficial for both the marine environment and human communities.