The small but mighty weapon against climate change …
Globally, there are many areas that need to be addressed in to mitigate climate change, but our oceans absorb around 25% of all carbon dioxide (CO2) emissions, making it one of the world's largest 'carbon sinks’.
This is because of its diverse coastal systems. Healthy coastal habitats play an important role in sequestering carbon, as well as providing seafood and recreation. These coastal systems are also known as ‘Blue Carbon’ and have a very significant part to play in the carbon cycle, and climate change.
This is a brief introduction to seagrass, just one of the blue carbon habitats that could be a natural solution to help fight against the climate crisis …
What is seagrass?
Seagrass is a type of marine plant that is found in shallow near-shore environments, often in a mix of salty and freshwater areas (known as ‘brackish’ water) such as estuaries. Seagrass is the only flowering plant able to live in this type of environment and pollinate while submerged. It often grows in large groups, creating underwater ‘meadows’ or ‘beds’.
What’s special about seagrass and why is it so important?
Seagrasses are often called foundation species or ecosystem engineers because they modify their environments to create unique habitats. Because of this, seagrass meadows act as an indicator species for environmental issues; as they rapidly respond to changes in their environment they can be used to provide insight into the overall health of the area. It can indicate if there is pollution or poor water quality, for example, or if the area has been overfished.
Seagrass can provide a vital ecosystem and habitat to our marine environment, and is valuable for many more reasons:
They have a complex three-dimensional structure formed by their roots, shoots, and leaves stabilises the sediment and can photosynthesise (i.e., produce oxygen) turning the sediment and the habitat into a rich, diverse ecosystem;
Seagrasses provide juvenile fish and shellfish with shelter, protection from predators, and increased food availability. The leaves support an array of attached seaweeds and tiny filter-feeding animals like sponges, sea squirts and molluscs. These provide food for small fish which feed the larger fish;
Seagrasses help improve and maintain high water quality by contributing to the exchange of nutrients between layers in the water column. Seagrass is known to play a crucial role in nutrient cycling by acting as both a sink and a source for nutrients in varying areas of nutrient availability; and
These meadows act as a nursery and hatchery for many commercial and economically important fish species (such as cod, which spend critical periods of their lives in seagrass).
These important ecological features also have a community benefit. As seagrass provides carbon sequestration, climate regulation, fisheries support (nurseries and hatcheries) and other biodiversity features – all of this increases tourism (through activities like bird watching and scuba diving), the cleaning of coastal waters and sediment stabilisation, and even reduces the impact of storms and bad weather.
Carbon
As mentioned, a significant feature for why it’s a key habitat is its ability to take carbon from the marine environment and emit oxygen. While seagrasses occupy only 0.1 percent of the total ocean floor, they are estimated to be responsible for up to 11 percent of the organic carbon buried in the ocean.
Just for context, one acre of seagrass can sequester 83 g carbon per square meter per year, the same amount emitted by a car traveling around 3,860 miles in a year.
Seagrass stores carbon differently to our terrestrial forests and at a greater rate as seagrass can sequester carbon into the sediment where it can’t remineralise back into the carbon cycle even if the seagrass has been cut down or removed.
Seagrass meadows have been found to bury carbon at a rate that is estimated to be 35 times faster than tropical rainforests, and their sediments don’t become saturated. Furthermore, while terrestrial forests bind carbon for decades, seagrasses meadows can bind carbon for millennia.
However, the significant capacity of coastal seagrasses to sequester carbon has gone unrecognised in models of global carbon transfer, and greenhouse gas abatement schemes. This is a major problem since the role of seagrasses as global carbon sinks continues to be threatened by coastal development and climate change.
Where is it found?
Seagrasses are broadly distributed in most of the world’s oceans and seas, extending right up into the Arctic Circle and as far south as New Zealand. Seagrass grows in semi-salty waters around the world, typically along gently sloping, protected coastlines. Because they depend on light for photosynthesis, they are mostly found in shallow depths where light levels are high. Strong wave action, nutrient concentration, ice scouring, depth and water turbidity are some of the limiting factors to the distribution of seagrasses.
The potential for seagrass is significant, as some 159 countries have seagrass on their shores, including the UK.
Historical Loss
As mentioned, seagrass distribution has rapidly been declining.
Globally, estimates suggest that we lose an area of seagrass around the same size as two football pitches every hour. Seagrass currently occupies 0.1% of the seafloor yet are responsible for 11% of the organic carbon buried in the ocean. An analysis of 215 published studies showed that seagrass habitat has disappeared worldwide at a rate of 110 km2yr-1 between 1980 and 2006. Of the 72 seagrass species listed in the IUCN Red List of Threatened Species, three are Endangered.
Historical Loss in the UK
Seagrass extent in the UK has declined dramatically over the past century, where 17% of all UK seagrass has been eradicated since the 1980s alone. This extensive seagrass loss is the result of a complex combination of factors that have fundamentally altered the UK coastline. Some of these factors include:
Coastal development, through physical removal of the habitat from activities such as dredging and fishing, as well as poor water quality remain two of the biggest issues for seagrass.
Extensive outbreaks of the seagrass wasting disease, Labyrinthula zosterae, have been ascribed as another cause of seagrass loss in Western Europe and the UK in the 1930s.
Poor water quality as result of environmental degradation reduced the seagrasses’ ability to survive.
Due to their shallow coastal location, seagrass beds often come into direct contact with humans, such as for anchoring of boats, fishing, and recreational activities.
Direct contact with coastal development areas, causing conflict between conservation interests and commercial development.
Indirect impacts from land activities, including sedimentation, eutrophication, and run-off of chemicals such as herbicides, further threatening seagrass health and survival through water pollution.
Once destroyed, seagrass ecosystems do not quickly recover as waves and currents erode the exposed seabed and inhibit regrowth. The combination of factors has led to severe degradation and loss of seagrass habitats around the UK that historically had been there for centuries.
Taken from the Seagrass Restoration Handbook (Ref 1).
The Future of Seagrass
As one of the most threatened yet overlooked ecosystems on Earth, seagrass meadows could have a promising future due to their ability to absorb carbon. Protecting what is left is vital, and if we can restore what has been lost, there is potential to have social, economic, and environmental benefits to our coastal waters.
Many organisations around the UK are tapping into the potential of seagrass. For example, Save Our Seabed is working with various facilities such as the Plymouth National Marine Aquarium that have labs to grow seedlings and can trial the best techniques to ensure the successful restoration of seeds and plantlets into places where they have been historically lost. The Catchment Based Approach have collaborated with a variety of stakeholders to produce restoration guides for seagrass as well as other blue carbon habitats.
Blue carbon strategies build on the opportunity to mitigate greenhouse gas emissions and to enhance organic carbon sequestration through the conservation and/or restoration of marine and coastal ecosystems, therefore acting as ‘natural capital’ resources.
Investing in the regeneration of these blue carbon habitats such as seagrass meadows would absorb massive quantities of carbon dioxide and would create long term carbon storage. For these reasons, seagrass restoration can be an economic incentive, as its restoration can offset emissions for organisations.
Seagrass meadows are a key habitat for many fish species, and other fish species in seagrasses are part of marine food chains which lead to commercially fished species. Arguably, one of the most important roles of seagrass is providing a nursery and shelter area for several commercially and recreationally important species. The increase in fisheries security means economically increased yield.
So, as an individual what can you do?
Lack of local public appreciation of the value of seagrass habitat is perhaps the greatest risk to its ongoing survival, as public opinion can impact restoration funding, policy, stakeholder engagement and involvement.
At home we can be more mindful about what we put in our waters and our individual impact. For example, what fertilisers you use in your garden, what is put down the drain, anchoring locations, bait digging for fishing, and so on.
There are also more prominent ways in which you can get involved. LIFE Recreation ReMEDIES have a project called Save Our Seabed which is currently holding two key volunteering events aimed at helping to restore seagrass in the UK. The first is a call for qualified scuba divers looking to help get seagrass seeds into seabeds. The second requires volunteers for seagrass seeds bagging, to get seeds ready for planting. The call for Seagrass seed bag packer volunteers has previously been in Plymouth, Portsmouth and Southampton of the UK.
However, there are a lot of global initiatives such as Global Seagrass Watch which uses an app to log and collect data on seagrass around the globe.
Public engagement is vital for the successful restoration and protection of these habitats. For example, in Australia, the Seeds for Snapper seagrass restoration project gained widespread community involvement and industry support once recreational fishers had recognised the value of seagrass beds as fish nurseries.
So with all it can do, seagrass really does have the potential to be the small but might weapon against climate change.
References:
Gamble C., Debney, A., Glover, A., Bertelli, C., Green, B., Hendy, I., Lilley, R., Nuuttila, H., Potouroglou, M., Ragazzola, F., Unsworth, R. and Preston, J, (eds) (2021). Seagrass Restoration Handbook. Zoological Society of London, UK., London, UK.
McLeod, E., Chmura, G.L., Bouillon, S., Salm, R., Björk, M., Duarte, C.M., Lovelock, C.E., Schlesinger, W.H. & Silliman, B.E. (2011) A blueprint for blue carbon: toward an improved understanding of the role of vegetated coastal habitats in sequestering CO2. Frontiers in Ecology and the Environment, 7, 362– 370.
Greiner JT, McGlathery KJ, Gunnell J, McKee BA (2013) Seagrass Restoration Enhances “Blue Carbon” Sequestration in Coastal Waters. PLOS ONE 8(8): e72469. https://doi.org/10.1371/journal.pone.0072469
