by Louise-Océane Delion, marine biologist and scientific content creator for Koraï
Introduction
What is hiding in the ocean, this vast blue space which covers 70% of planet Earth and represents 90% of its habitable space? What do we see when we go explore the living world under the sea?
And more importantly, where is life in the ocean?
Although the ocean is a huge, wide and deep space - 4 000 metres on average - not all marine life is evenly distributed.
In fact, a large majority of marine biodiversity is found near the coasts, in relatively shallow waters, where the sunlight still penetrates.
In this article, we are taking you on a journey to discover these ecosystems which are home to the majority of marine species. More specifically, we invite you to discover the coastal ecosystems of Africa.
Because with its 26,000 kilometres of coastline and surrounded by two oceans - the Atlantic to the west and the Indian to the east - Africa has some incredible coastal ecosystems and, as a result, a thriving marine biodiversity.
While anthropogenic pressures are more than ever affecting the ocean and marine biodiversity, there is still room for action to protect existing marine ecosystems and facilitate the recovery of those already impacted.
To do this, discovering and understanding these ecosystems is essential, as it serves as a starting point to move forward together towards the accomplishment of Koraï's mission: to regenerate Africa's marine ecosystems. Will you join us?
Coastal ecosystems of Africa
There are three main marine ecosystems along the African coast:
Seagrass meadows
Mangrove forests
Coral reefs
Together, these three ecosystems cover an area of 117,000 km21 - a significant area, rich in life, providing many economic, cultural and other types of services to African coastal populations.
Seagrass meadows
Not to be mistaken for algae, seagrasses belong to the family of flowering plants. They are actually the only flowering plants found in the ocean and are able to reproduce there, either sexually through seeds or asexually by cloning themselves.
Because of their need for light for photosynthesis, seagrasses are found in shallow waters. They grow in different types of seabed - usually sand or muddy sediments in which they can take root. The plants live in colonies and form large patches of seagrass, commonly known as seagrass meadows.
Seagrass meadows are found all along the African coastline and are the most extensive coastal ecosystem of the continent with an estimated area of 72,000 km21 . However, their greatest diversity and abundance is found along the coastal zone between Guinea-Bissau and Angola with over 43,000 km21 of seagrass beds present in this region.
Mangrove forests
Mangroves, also known as mangrove forests, form a unique ecosystem at the frontier between the land and the sea.
This ecosystem is made up of different species of trees that have the ability to survive in particular conditions, resisting sharp changes in salinity, temperature and desiccation caused by, among other things, the ebb and flow of the tides and the mixture of water coming from the land and from the sea.
Mangroves are the second largest coastal ecosystem on the African continent, extending over 27,500 km21. The majority of mangrove forests are found along the coast of the Gulf of Guinea as well as along the eastern coast of the continent, from southern Somalia to southern Mozambique, including the iconic Rufiji River Delta wetland in Tanzania, one of the largest mangrove areas in Africa (>53,000 hectares)1.
Coral reefs
Probably one of the most iconic marine ecosystems in the world, coral reefs are also very present in African coastal waters.
Despite what their shape and structure might suggest, corals are large colonies of small animals, called polyps. Cousins of anemones and jellyfish, these polyps live in symbiosis with a small alga, the zooxanthellae, which finds shelter inside the polyp. In exchange for a place to grow, the alga provides the coral with nutrients that it produces through photosynthesis.
By growing a common skeleton, these polyps create large reef colonies, mostly in shallow waters. Within the African continent, there are numerous coral reefs, both in the relatively cold waters of northwestern Africa (Atlantic Ocean) and in the relatively warm waters of southeastern Africa (Indian Ocean).
African coral reefs cover more than 17,500 km2 and more than a third of them are found along the Agulhas Current - from South Africa to southern Tanzania, including Madagascar1.
Conclusion
Seagrass meadows, mangrove forests and coral reefs are the hotspots of marine biodiversity in Africa. Their presence along most of the African coastline and their large extent highlight the diversity and quantity of marine life present in African waters.
Unfortunately, these coastal ecosystems have been under significant anthropogenic pressure for decades and are disappearing on a global scale, and African ecosystems are far from being spared.
It is exactly to act against this that Koraï has given itself an ambitious mission: to regenerate African coastal ecosystems. Will you join us?
References
1Tregarot, E., Touron-Gardic, Gré., Cornet, C.C., Failler, P., Valuation of coastal ecosystem services in the Large Marine Ecosystems of Africa, Environmental Development (2020), doi: https://doi.org/10.1016/j.envdev.2020.100584