coastal habitats

Coastal habitats, mangroves, tidal marshes, kelp forests and seagrass beds, are of immeasurable ecological importance to the planet as they provide:

• a habitat for numerous marine species;

• natural protection against flooding and coastal erosion;

• a filter for the water around them, reducing acidification and sometimes even filtering out microplastics; and

• a storage facility for carbon dioxide.

Their ability to sequester carbon has earned them the name ‘blue carbon’. 23% of global emissions of CO2 are absorbed by the ocean and half of that by coastal plants. Mangrove forests, for example, sequester up to 10 times more carbon per hectare than tropical rain forests. However each of these coastal ecosystems is under threat from many angles:

• draining or clearing for coastal development;

• conversion to agricultural land;

• over-harvesting;

• destructive fishing practices;

• coastal pollution;

• rising sea levels; and

• warming temperatures.

As with deforestation on land, by destroying these habitats not only do we lose their positive effects but when degraded their blue carbon effect goes into reverse: they emit the carbon they have stored for centuries and become sources of greenhouse gases. Experts estimate that as much as 1.02 billion tons of CO2 are being released annually from degraded coastal ecosystems, a process which needs to be reversed.

Mangroves are trees or shrubs that are found in the inter-tidal zone of coastlines. There are about 70 species of mangroves found along tropical and sub-tropical coastlines, particularly in Asia, Africa and South America. Mangrove trees have filtration systems that allow them to filter out the salt from the changing tides. Their root systems extend above and below the water, offering habitat, nurseries, and feeding grounds for a vast array of fish and other marine life. Mangroves cover about 12% of the 1,634,701.00 km of the global coastline but are being lost at a rate of 2% per year.

Tidal marshes are coastal wetlands with several metres of soil made up of mineral sediment and organic material which is flooded with salt water brought in by the tides. Tidal marshes capture CO2, filter pollutants from land runoff and help maintain water quality in coastal areas. They provide a habitat for many important marine species and serve as a buffer to coastal communities, absorbing some energy from storms and floods and helping to prevent erosion. Tidal and freshwater marshes are being lost at a rate of 1-2% per year. They cover roughly 140 million hectares of the Earth's surface but have already lost more than 50% of their historical global coverage.

Seagrasses are found in shallow salt and brackish waters in the coastal waters of most parts of the world, from the tropics to the poles. Seagrasses are closely related to terrestrial plants with roots, stems and leaves, flowers and seeds. They support biodiversity, providing a habitat for many smaller marine animals, acting as nursery areas for juveniles, providing both food and feeding grounds as well as refuge from predators. Just as importantly they capture CO2 from the atmosphere and filter the water, removing excess nutrients and even microplastics (the species Posidonia oceanica can trap 1,500 plastic particles per kilogram of seagrass each year). Seagrasses are believed to be the third most valuable ecosystem in the world (only topped by estuaries and wetlands): one hectare of seagrass is estimated to be worth over EUR 16,000 a year. Seagrasses cover less than 0.2% of ocean floor, but store about 10% of the carbon taken up by the ocean each year. Seagrasses are being lost at a rate of 1.5% per year and have lost approximately 30% of historical global coverage.

Kelp forests are underwater versions of our terrestrial forests: intricate ecosystems found in shallow coastal water where several different species of kelp create a habitat for many species of invertebrates, fishes, and other algae. Kelps are large brown algae which thrive in cold, nutrient-rich waters and can grow up to 45 metres in height (sometimes at the amazing rate of about 60 cm a day). Like terrestrial forests, kelp forests absorb a lot of carbon dioxide and are an important tool in carbon sequestration.

dive in deeper

Map of mangrove coverage

Read more about mangroves

NASA Mangrove Science Page

Global Mangrove Alliance: State of the World’s Mangroves 2024

Only One: Mangroves: The unsung climate heroes
Copernicus Marine Environment Monitoring Service: Coastal Zones datasets for the 700,000 km2 of Europe’s coastal land areas for 2012 and 2018 and a change layer for 2012-18
Kelp Deforestation: Threats to our Underwater Forests
Kelp Forests Beneath the Sea: A Vital Habitat
(Kelp) Forests of the Sea
Help!! What’s kelp!!
The Marine Diaries

Read more about seagrasses

Out of the Blue: The Value of Seagrasses to the Environment and to People
UNEP/GRID-Arendal/UNEP’s World Conservation Monitoring Centre (UNEP-WCMC).