Underwater meadows to guard the climate

Underwater meadows, are coastal areas of seas, oceans, as well as lakes, rivers and other bodies of water, covered with dense vegetation. They mainly consist of seagrasses, algae and other vascular plants. These ecosystems play an important role in the environment, performing many ecological functions. Seagrasses around the world contribute to climate stabilization and carbon sequestration, let’s take a closer look at them.

Underwater grasslands and biodiversity

Seagrasses, which are flowering and seed-producing plants, are rooted in the seabed. Their growth is only possible at depths where sunlight can reach – usually no more than 40-70 meters. They form extremely rich ecosystems that serve as habitat for many aquatic species. Among the dense grasses, fish and invertebrates can safely reproduce and reach maturity. On top of this, these areas abound with food for fish and medium-sized predators, which is provided by invertebrates such as clams, sponges, anemones and sea urchins. Larger animals also readily feed on plankton, algae living on grass leaves and grasses themselves.

One acre (about 0.4 hectares) of underwater meadow can provide food for more than 40,000. fish and 50 million invertebrates. Studies have shown that these areas are home to approx. 100 times more animals than in the surrounding bottom areas not covered with grass. An example of the biodiversity of underwater meadows is the Sado estuary in Portugal. There, seagrass beds create habitat for species valuable to traditional fisheries such as cuttlefish, dorado and sole. Underwater meadows also support species important for marine conservation and tourism, such as seahorses and bottlenose dolphins.

Underwater meadows – ecosystem services

Underwater meadows stabilize marine ecosystems by reducing water ripples. Their compact structure not only reduces bottom erosion, but also acts as a natural filter. Sediments suspended in the water, before they settle to the bottom, are cleaned by seagrasses of heavy metals and harmful bacteria. Through this process, the water becomes much cleaner, which promotes the health and diversity of marine life. This is why underwater meadows are often referred to as ecosystem engineers.

These unique ecosystems are also of significant economic importance. The species that live among them, such as fish and shellfish, are valuable to fisheries. Seagrass around the world supports fishing activities, providing the foundation for 20 percent. of the world’s 25 most important fisheries. Thus, underwater meadows not only protect the environment, but also contribute to the sustainability of local and global economies.

Submerged meadows also play their role in protecting the seashore, protecting it from erosion and minimizing the risk of flooding and storms. These unique ecosystems also participate in biogeochemical cycles – the carbon and nitrogen cycles. Particularly valuable is their impact on water quality: seagrasses, such as the Zostera noltei species, can effectively remove nitrogen from municipal and agricultural wastewater. Studies indicate that one hectare of this grass can remove as much as 510 tons of nitrogen per year from marine waters.

Economists have estimated that the value of the ecosystem services provided by sea meadows, related only to nutrient cycling, exceeds the 25,000. euro/ha per year. However, the most valuable service that underwater meadows offer is carbon sequestration. Although they occupy less than 0.2 percent. of the ocean floor, each square kilometer of this vegetation can tie up to 83,000. t of carbon per year – making them twice as effective in this role as forests of comparable size, which can absorb about 30,000. t of carbon.

Seagrasses store carbon not only in their biomass, but especially in the soil, where as much as 90 percent. of the carbon is bound long-term. As perennial plants, seagrasses can tie up carbon for centuries, and if the grasslands remain undisturbed, this potential persists for up to millennia. This ability to sequester carbon over the long term is impressive, especially compared to terrestrial ecosystems, which typically only retain carbon for decades or centuries.

Threats and protection of underwater meadows

Since the late 19th century. The world has lost about one-fifth of its marine grasslands due to anthropogenic changes. The degradation of these ecosystems is due to a number of factors, including:

• Water pollution from urban, agricultural and industrial wastewater;
• Coastal infrastructure development;
• dredging of estuaries;
• destructive fishing methods and uncontrolled anchoring damaging leaves and rhizomes;
• climate change, causing more intense storms, floods and heat waves.

Any destruction of these valuable plants means the release of some of the carbon they store into the environment. Therefore, initiatives are being developed to protect and restore underwater meadows. Techniques involving transplanting whole plants or young shoots and planting seeds have been developed. These methods are used depending on local environmental conditions and the type of seagrass.

One example of such activity is the action organized in February 2023. off the coast of Wales. Industrial development there has caused, over the past century, the disappearance of 92 percent. underwater grasslands. In response to this alarming decline, WWF, in cooperation with other organizations, has undertaken the planting of 5 million seagrass seeds. The goal of the project is to restore at least 10 hectares of meadows in the coastal zone by 2026, helping to protect biodiversity and stabilize the local marine ecosystem.