What Bleaching Actually Does to a Coral Reef – And Why It’s a Big Deal

by Anisa Muridi

When people imagine coral reefs, they usually picture vibrant underwater cities, full of life and colour. However, with rising ocean temperatures, many of those colours are quietly fading to white.

That is called coral bleaching, and it has also affected the Shimoni region, along the southern Kenyan coast in 2024. The sea is warmer than usual, and the reefs are stressed. For many of us working closely with the ocean, these moments feel heavy and uncertain, but not hopeless.

Understanding what bleaching really is, what causes it and what it means for local communities is more than just learning about marine science. It’s about tuning in to the silent signals coming from the sea and deciding how we respond.

What Actually Happens When Corals Bleach?

Corals are not just rock-like structures or decorations on the ocean floor. They are living animals that survive through a delicate symbiotic partnership with tiny algae living inside their tissues. These algae, called zooxanthellae, are what give corals their beautiful colours. More importantly, they provide most of the coral’s energy through photosynthesis.

However, when ocean temperatures rise, especially for prolonged periods, corals become stressed. In response, they expel the algae from their tissues. What’s left is a pale, almost ghostly-looking skeleton. This is bleaching. It doesn’t mean the coral is dead, but it’s a sign that it’s struggling and without their algae partners, corals begin to starve.

Coral reefs support a quarter of all marine species. That means when reefs bleach, fish populations also suffer. Sea creatures could lose their homes. 

The longer the corals stay bleached, the more likely they are to die. When large areas bleach at once, it’s a red flag for the entire ecosystem.

Why Is It Happening More Often?

As a consequence of climate change, sea surface temperatures across the globe are rapidly rising, putting immense pressure on coral reefs. In 2024, the world experienced one of the largest global bleaching events ever recorded and Kenya was not spared.

Other factors add to the stress. Pollution, sediment runoff and destructive fishing practices, such as bottom trawling, weaken the reef’s ability to recover. Dragging heavy nets across the seabed, destroying several ecosystems and habitats at once. Trawling also results in bycatching, meaning most species caught in the net are discarded dead back into the sea. 

Coastal development and unregulated tourism can worsen the situation. It’s a web of pressure points, and when one snaps, others often follow.

How does it affect the locals?

The ripple effects are wide and they reach the surface too. In Kenya, millions of people depend on the ocean for food, income and protection from storms. Coral reefs act like natural breakwaters, softening the force of waves before they hit the shore. They also fuel the tourism industry, which brings jobs to coastal communities.

Protecting coral reefs is not just about losing beauty. It’s about losing biodiversity, economic stability and protection for people living near the sea.

What We Are Doing at REEFolution

Trying to plant corals in a stressed reef could do more harm than good. After a pause in direct restoration activities, our team is outplanting again. We are currently increasing our nursery capacity, repopulating old nursery structures with new, heat-resilient corals. We also started re-planting surviving and heat-resilient corals onto our artificial reefs in August. So far, we’ve successfully replanted and outplanted over 3,000 corals.

Education remains a key part of our work during this time. We are continuing school sessions, community talks and digital storytelling to help others understand what is happening beneath the waves. In partnership with Wageningen University, students and rangers are doing long-term reef monitoring throughout the coming months. The goal is to understand how the oldest reefs have been faring over time. The monitoring is conducted partially on replanted corals, while the other half is done without replanted corals, to see how they recover without intervention.

Reef restoration is not a one-season effort. It’s about building resilience over years, sometimes decades. That’s why we use techniques like coral gardening, alternative substrates artificial reefs (like our glass bottle reefs and reef stars) and partnerships with local communities to help the reef recover when conditions improve.

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