In an article for Halloween, Grace Cutler, one of Project Seagrass’ Interns for the 2025-26 academic year, explores the frightening reality of continued seagrass loss as a result of anthropogenic activity and how this in turn threatens seagrass’ role in supporting people and planet. Werewolves are struck down by silver
Seaweed farming is a rapidly expanding global industry. As a food resource, it has high nutritional value and doesn’t need fertilisers to grow. Seaweed provides valuable habitats for marine life, takes up carbon and absorbs nutrients, plus it helps protect our coastlines from erosion. Usually, seaweeds grow on hard, rocky surfaces. Yet, to
In an article for Halloween, Grace Cutler, one of Project Seagrass’ Interns for the 2025-26 academic year, explores the frightening reality of continued seagrass loss as a result of anthropogenic activity and how this in turn threatens seagrass’ role in supporting people and planet. Werewolves are struck down by silver bullets, vampires are defeated with wooden stakes; the environment is protected by seagrass. While it may not be as dramatic, the narrative that aligns seagrass as the ultimate solution to combating the environmental crisis is popular. As someone studying this remarkable habitat, it’s easy to see why. The only marine flowering plant in the world, seagrass offers numerous ecological benefits, supporting both our planet and humanity. Despite this, we risk ignoring the crux of the issue by relying on these green solutions. We keep polluting. It is because we continue to pollute our environment, be it through greenhouse gases, plastic pollution, or general waste production, that the very things that help to prevent the environmental crisis, are dying. A Natural Water Filter? While seagrass may not clean water bodies, it increases particle deposition rates by slowing the speed of waves and allowing more time for particles to sink to the ocean floor. Particles can then become trapped in the seagrass meadow and are prevented from ending up elsewhere in waterways. This process has been shown to capture excess nutrients, waste products, and even pathogens. A study conducted in the greater Seattle Metropolitan Area showed that mussels placed in seagrass habitats had 65% less relative abundance of some pathogens when compared to mussels placed in habitats without seagrass. Yet, the most apparent threat to seagrass, identified by UK researchers, is water quality. Like most plant species, seagrass can function in polluted water quality up to a point or ‘threshold value’. Similar to how humans can eat a certain number of toffee apples until it becomes too much and we get a sugar crash. Once this threshold is exceeded, seagrass will decline and, in some severe instances, disappear from the environment entirely. One such instance can be seen in the Chinese province Hainan, where researchers found that a dissolved inorganic nitrogen concentration of 8μM or above will cause seagrass meadows to disappear. This is because an excess of nutrients in water bodies, like nitrogen, stimulates the production of algae which blooms on the surface of the water and prevents sunlight from reaching seagrass beds. Additionally, some nutrients like ammonium and sulphides can have direct negative effects on seagrass growth. Fortifying our Coastlines Imagine a castle that is under attack. If it is strong and maintained, the castle will be better at defending itself against intruders. However, the next time it is under attack, there are holes and weak points left in it from the previous battle. Over time, this castle falls into disrepair and becomes a ruin, leaving it unable to protect its inhabitants. Seagrass is similar. Its inhabitants are our coastlines. Coastlines today are facing threats on all fronts. Sea level rise, extreme storms, and erosion are just some of the problems they experience. With that said, some have considered using seagrass as a way of minimising the impact of storms causing erosion in these areas. Through their matted root systems, called rhizomes, seagrass meadows have been shown to improve the stability of sediments and reduce wave energy before it reaches the shore in some hydrodynamic systems. Yet, seagrass is also harmed by these storms. Meadows that are struck by intense physical disturbances can be uprooted or die back, initiating a positive feedback loop where meadows in decline are more vulnerable to disturbances. This means when the next storm hits, seagrass not only will be more susceptible to decline, but they are also less able to protect our coasts. What About Carbon? Carbon storage is a phrase often thrown around. It may be the key reason why people are interested in seagrass as an answer to climate change. With anxiety surrounding our warming planet on the rise, this isn’t unprecedented. However, seagrass may not be quite the antidote we think it is. Recent evidence has shown that following disturbances, carbon stored in the soil of meadows may be re-released into their environment as carbon dioxide. Such disturbances can range from direct physical effects, such as dredging and construction work, or indirect global threats stimulated by climate change. A 2011 marine heat wave struck the West-coast of Australia, causing the reported loss of over 1000 km2 of seagrass in Shark Bay. Another instance of mass seagrass loss occurred in the Gulf of Mexico, where two seagrass species (Halodule wrightii and Syringodium filiform) disappeared following sea level rise in 2014. Without seagrass, the carbon stored in these soils is easily remineralised and released back into the environment. What’s Next? Thankfully, the main factor contributing to seagrass decline appears to be anthropogenic impacts such as dredging, overfishing, and agricultural runoff. This means that with changes in how we do things, we can stop the death of seagrass. However, this means seagrass mustn’t be painted as a plaster to patch up the pollution of the planet. To help seagrass, we must reduce pollution, reduce nutrient runoff, protect seagrass so it can protect us! References Ranking the risk of CO2 emissions from seagrass soil carbon stocks under global change threats Extreme climate events lower resilience of foundation seagrass at edge of biogeographical range Too hot to handle: Unprecedented seagrass death driven by marine heatwave in a World Heritage Area Rapid sea level rise causes loss of seagrass meadows Seagrass ecosystems as green urban infrastructure to mediate human pathogens in seafood Toxic effects of increased sediment nutrient and organic matter loading on the seagrass Zostera noltii Losses and recovery of organic carbon from a seagrass ecosystem following disturbance Continual migration of patches within a Massachusetts seagrass meadow limits carbon accretion and storage Mediterranean seagrasses provide essential coastal protection under climate change
Seaweed farming is a rapidly expanding global industry. As a food resource, it has high nutritional value and doesn’t need fertilisers to grow. Seaweed provides valuable habitats for marine life, takes up carbon and absorbs nutrients, plus it helps protect our coastlines from erosion. Usually, seaweeds grow on hard, rocky surfaces. Yet, to farm seaweed, potential areas need to be easily accessible and relatively sheltered. This is where seaweed can grow with limited risk of being dislodged by waves. Seaweed farms in Asia, in countries like China and Indonesia, are responsible for more than 95% of global seaweed production. Seaweed farms, particularly those in Southeast Asia, are commonly in the very same environments where seagrass meadows thrive. Competition for resources ensues. Evidence shows that tropical seaweed farms, when placed in or on top of tropical seagrass meadows leads to a decline in the growth and productivity of seagrass. There is also evidence that seaweeds outcompete seagrasses in cooler waters, especially when nutrients in the water are very high. Despite negative interactions, such as shading, between seaweed and seagrass, some scientists now advocate for a global expansion of seaweed farming in areas where seagrass grows. This call, comes at a time when seagrass global initiatives are trying to stem seagrass loss. Efforts are underway to expand these habitats to their once extensive range to help fight climate change and biodiversity loss. Seagrass meadows are a crucial store of carbon, providing habitats for a wide array of animals. Why farm seaweed on top of seagrass? The reason that some scientists are advocating for farming seaweed in seagrass is that their research claims that the presence of seagrass reduces disease causing bacterial pathogens by 75%. A major win for a relatively low tech industry where seaweed disease outbreaks hinder production. These scientists are not the only ones advocating for seaweed production at scale. Global conservation charities, like World Wildlife Fund and The Nature Conservancy, as well as the Earthshot prize launched by Prince William all support seaweed cultivation programmes in areas likely to contain abundant seagrass. However, together with other scientists, we have argued in an academic response in the journal PNAS that their claim is premature. We are concerned that, without appropriate management, these seaweed programmes threaten marine biodiversity and the benefits that humans get from the ocean. Despite historic and globally widespread seaweed cultivation, effects on seagrass have mostly been ignored. Where studies exist, effects have been negative for seagrass, its ability to capture carbon, and the diverse animals that call it home. Entanglement of migratory animals, such as turtles and dugong with seaweed also needs wider consideration. This is especially the case given new legal frameworks to protect their habitat, and there is ongoing concern for these species being killed by seaweed farmers. The equity of coastal fishing grounds also comes into question, as communities that use seagrass for fishing are most likely to lose access. Conservation charities advocate for tropical seaweed farms for good reason. This is to improve community resilience in the face of degrading coral reefs and overfishing. While projects mostly have the best intentions, they often don’t consider cascading unintended consequences, nor the equity of the whole community. In reality, seaweed farm placement is effectively akin to ocean grabbing (the act of dispossession or appropriation of marine resources or spaces) with farmers winning on a “first come, first serve” basis, despite not owning the seabed. Some seagrass meadows in Zanzibar, Tanzania, have recovered since seaweed farms have been removed. GoogleEarth Sustainable standards If seaweed farming is to be expanded, standards for sustainability must be upheld and strengthened. In 2017, a sustainable seaweed standard was launched by the Aquaculture and Marine Stewardship Councils. But few tropical seaweed farms meet the criteria outlined in this standard due to known consequences that affect seagrass (rightly defined in the standard as vulnerable marine habitats) and likely negative effects on endangered species, like dugong, that frequent seagrass habitats. Seaweed cultivation strategies have mixed evidence for long-term success. In Tanzania, many farmers have abandoned the industry due to low monetary rewards compared to the investments they put in, and some evidence suggests that the activity reduces income and health, particularly for women. Where seaweed cultivation has been implemented to reduce fishing pressure, it has instead increased (and often just displaced) fishing activity. Given the rapidly increasing threats faced by tropical marine habitats despite the role they play in climate resilience, understanding trade-offs prior to large scale expansion of seaweed farming is a priority. To reduce further any negative effects, international programmes and research advocating for large-scale seaweed farms need to align more readily with the seaweed standard. More information: This article was published in The Conversation Jones. et al, Risks of habitat loss from seaweed cultivation within seagrass, PNAS (2025). https://doi.org/10.1073/pnas.242697112 Seaweed farms are often placed on top of seagrass meadows. Niels Boere/flickr A women prepares seaweed ropes for deployment in the Wakatobi, Indonesia. Benjamin Jones/Project Seagrass
