ocean habitats (coastal habitats)

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.

What can we do to protect them?

protection: area based management, such as by designating marine protected areas, is an effective way to protect these ecosystems from excessive use or harm by people;
restoration: regrowing or reforesting the ocean (known as ocean afforestation) can turn the ocean into a giant carbon sink. Projections have been made to the extent that if just 9% of the ocean surface were afforested, we could remove 53 billion tons of CO2 from the atmosphere each year, completely balancing out our current level of emissions.

Examples of organizations working in this field are the International Blue Carbon Initiative, a global program focused on mitigating climate change through the conservation and restoration of coastal and marine ecosystems, SeaTrees, which supports communities planting and protecting blue-carbon coastal ecosystems and the Global Mangrove Alliance.

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.

The 72 different types of 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 0.1% of ocean floor, but store about 30% of the carbon taken up by the ocean floor each year. They support the productivity of 20% of the world’s biggest fisheries by providing a nursery habitat for them. 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.

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Map of mangrove coverage