Corals reefs, the rainforest of the sea

Over a third of coral reefs – corresponding roughly to the size of England – have been irreversibly lost in the last 30 years and 60% of the remaining coral reefs are threatened to disappear within the next 30 years. Some scientists even predict that corals will be extinct all together by 2100. Facing this alarming picture, PUR Projet launched its first marine project in 2016 in the Northwest of Bali – after all coral reefs have a lot in common with tropical rainforests!
This project was developped by Emilia D’Avack. Holding a Masters in Marine Biology and a Bachelor degree in Sustainable Development, she joined PUR Projet in 2015. She was perfectly placed to bridge the gap between marine and terrestrial environments.

Emilia D'Avack coordinating Pejarakan coral reef restauration project
Emilia D’Avack coordinating Pejarakan coral reef restoration project, April 2018, Credits: Zoé Bassetto

Final checks are done, the tank on my back is full of compressed air and my SCUBA equipment is safely secured. I press a hand on my mask and fall backwards into the warm water. I open my eyes and I am immediately surrounded by a spectacle of light and colour. The coral reef beneath me is teeming with life: a pufferfish lazily lies on a brain coral; damselfish are darting around protecting their farmed patch of algae against potential intruders, tiny blue chromis fish are hiding within the intricate branches of an acropora coral and a curious cuttlefish rapidly changes colour patterns whilst edging closer to my left fin.

At the heart of this manic activity are the corals themselves. Found in diverse shapes, sizes and colours they do at first glance seem like inanimate rocks – but this could not be further from the truth. Each colony is composed of thousands of tiny identical individuals, each a perfect clone of its neighbour. Their elaborate structure, providing hiding, breeding as well as hunting places for the immense range of organisms around me, is the cornerstone of the entire reef ecosystem. Just like trees in a forest, they are at the foundation of the trophic food chain and support the multitude of life found in tropical reefs, which accounts for a staggering 25% of all marine biodiversity (with over 2 million different species!). And as with trees in a forest, their disappearance would cause the collapse of the entire ecosystem.

On corals and trees 

Is it not by accident that coral reefs are often described as the tropical rainforest of the sea, their similarities to forest ecosystems go well beyond the provision of habitat. Indeed, trees depend on sunlight through photosynthesis for survival – and so do corals! Within their tissues lives a microscopic alga called zooxanthella. The algae and the corals form a symbiotic relationship, meaning that both organisms require each other for their survival. The algae photosynthesises during daytime hours thereby converting enough sugars from sunlight for itself and the coral. In turn for this secure food source, representing over 90% of its nutritional needs, the coral provides a safe home within its living tissue to the algae.

This crucial relationship is however threatened by changes in the ocean brought along by climate change. As the surface water warms above a certain threshold, the heat-stressed coral ejects the algae and in doing so faces potential starvation. This phenomenon, known as bleaching as only the bone white coral skeleton is left behind, has contributed to the rapid decline of coral reefs worldwide. Although corals can recover from bleaching when the water temperatures drop fast enough, persistent bleaching can cause the death of entire coral reefs. The persistency and the frequency of coral reefs bleaching have changed over the past decades, with severe bleaching events becoming 5 times more frequent than 40 years ago. This leaves little to no time for corals to recover, resulting in global diebacks. The decline of coral reefs has important repercussion not only on the biodiversity they support but also on the 850 million people that live within proximity to a coral reef. Many of these people live in developing countries and island nations where dependency on coral reefs for food and livelihoods is very high. Indeed, just as trees supply food, building materials, etc., corals provide a vast range of resources to us humans too. If sustainably managed, 1 ha of reef can produce up to 200kg of fish each year. The reef is also a great source for medical advances, with substances acquired from the reef already used in the fight against HIV and cancer, with many more yet left to be discovered.

The parallels between tropical forests and coral reef don’t stop here. Whilst trees provide protection from extreme weather events (storms, floods, landslides…), corals protect the coastline against storms and hurricanes by effectively dissipating wave energy before making landfall. Both ecosystems also help to rid their environment of pollutants. Trees decontaminate soils and water runoffs and filter out excess fertilization, chemicals and heavy metals, coral reefs provide very similar services through the wide range of filter feeders and sponges found on the reef that filter out contaminants from the seawater.


Quantifying ecosystem services

Trying to quantify all the services provided by corals reefs is a complex task, but a TEEB report (Economics of Ecosystems and Biodiversity) estimated that a hectare of healthy coral reef provides up to 1.2 million USD of free ecosystem services each year (versus 10,000 USD for tropical rainforests). This makes coral reefs the ecosystem with the highest economic value found on our planet. As well as these economic benefits, coral reefs also have an inherent spiritual and traditional importance, an intrinsic value found in various forms across the globe and among nearly all populations that live in reach of a reef and that cannot be quantified in monetary terms. It is important to remember, that although out of sight and hidden below the waves, we cannot afford to forget about the incredible coral reefs. It is our duty (and best interest) to do everything in our power to protect them for generations to come.

Underwater I only hear my own breathing, sending columns of bubbles dancing to the surface. But then a multitude of sounds become audible – the crunching from a parrotfish jaw chomping away on a nearby coral colony, clownfish barking at anyone getting too close to their anemone home, the flicking of tails as a school of snappers take a sharp turn to avoid a hungry barracuda… When you pay attention, the whole water is filled with scratches, shrills and bangs combining in a deafening underwater chorus reminding me of the sounds of a rainforest at dawn.

Written by Emilia d’Avack
PUR Projet Marine expert


Know more about marine ecosystems restoration

Costanza, R. et al. (2014) Changes in the global value of ecosystem services, Global Environmental Change
Hughes, T. P. et al. (2018) Spatial and temporal patterns of mass bleaching of corals in the Anthropocene, Science
World Resource Institute


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