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Coastal ecosystems: biodiversity hotspots

by Louise-Océane Delion, marine biologist and scientific content creator for Koraï

While the ocean is a vast, wide and deep space full of life, this life is not evenly distributed. As mentioned in our previous article, the majority of marine life is found near the coast and in shallow waters. Mangrove forests, seagrass meadows and coral reefs are the homes of marine life and between them support the majority of the marine living web.

In this new article, we invite you to dive into these coastal ecosystems and discover the rich life found there, understand why it is highly concentrated there and why it is so necessary to preserve and regenerate these threatened places.

More complexity for more biodiversity

Coastal ecosystems such as mangrove forests, seagrass meadows and coral reefs bring unique complexity and three-dimensional structure to the ocean.

The shapes created by the reefs, roots or even stems create a much more complex habitat than a simple water column in the open ocean. This results in numerous niches, cracks and crevices where marine species can thrive in.

The more complex the structure of a habitat, the more species can live in it - up to a certain threshold. It would be like increasing the number of rooms in a house, which can accommodate an increasing number of different guests... Each species has its own specific needs and these habitats become breeding, refuge and feeding grounds for a large majority of marine species.

Many animals come to these habitats only for part of their life cycle, notably by using them as nurseries. They come to breed in the calm and protected waters: the offspring spend a while in these coastal areas to grow before being able to leave for the open sea, where they will continue their lives before returning to these coastal areas to reproduce themselves.

An inter-systemic connection

Mangrove forests, seagrass meadows and coral reefs do not exist independently but are rather interconnected, with marine species moving from one to the other at different stages of their development.

For example, it is very common for fish species to lay their eggs in coral reefs. The fish larvae find their way to the very calm and shallow waters of the mangrove where they can develop. Once they have reached a certain size and stage of development, these fish will continue part of their development in the seagrass beds and return to the coral reefs.

It is therefore very common to find several of these ecosystems - often all three - in close proximity to each other as each plays an important and distinct role for the same species. This interconnectivity also reminds us that damage to one ecosystem will have consequences for all ecosystems and for marine biodiversity as a whole.

Hotspots of biodiversity

There is a wide range of species living in these ecosystems: fish, crustaceans, molluscs, reptiles, birds, mammals, amphibians, etc. The life forms that can be found there are numerous and diverse. For example, 25% of marine biodiversity is found in coral reefs1 !

These ecosystems are vital for the vast majority of marine biodiversity. They are perhaps even more vital for certain species that use these habitats as a migration zone or for certain endangered species that find refuge there.

In the case of Africa, for example, the majority of mangrove forests are important passage points for migrating birds. The coastal waters where reefs and seagrass beds mix are home to many iconic species such as turtles, rays, crocodiles, and sharks...

Humans: a species depending on coastal ecosystems

If there is another species that depends on these ecosystems, it is us, human beings.

The abundance of life in coastal waters has made it profitable for us to use these habitats as feeding grounds. Either directly by catching the animals in these coastal habitats or by going further out into the open ocean, where the fish that have finished their development in the coastal waters have come to continue their lives in a larger space.

Local fisheries are entirely dependent on the health of these coastal ecosystems, as these ecosystems ensure the health of the marine populations on which we depend for food.

The abundant beauty that lies beneath the water in marine ecosystems, bursting with colours and shapes, is also a source of inspiration for many of us. The rise of tourist activities such as diving, snorkelling, kayaking etc. is also evidence of the link between our species and these ecosystems.

Taking care of these ecosystems

It is exactly because the entire living world - marine species, some coastal and terrestrial species, and us - depends on mangrove forests, seagrass meadows and coral reefs, that we must respect, protect and regenerate these ecosystems.

Today, coastal ecosystems face many anthropogenic pressures: urbanisation, coastal development, climate change, and direct exploitation...2 But we cannot afford to lose these marine ecosystems because their loss would also mean the loss of a great part of the living world of the ocean, as well as our own.

Fortunately, we now have the knowledge and capacity to act in time. This is why Koraï has set itself an ambitious mission: to regenerate Africa's marine ecosystems. Will you join us?


1Plaisance L, Caley MJ, Brainard RE, Knowlton N (2011) The Diversity of Coral Reefs: What Are We Missing? PLoS ONE 6(10): e25026.

2IPBES (2019): Global assessment report on biodiversity and ecosystem services of the Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services. E. S. Brondizio, J. Settele, S. Díaz, and H. T. Ngo (editors). IPBES secretariat, Bonn, Germany. 1148 pages.


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