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Writer's pictureHarry Smith

Will coral shades save corals from dying from bleaching?

Updated: Aug 26

Corals are facing a silent crisis: heat stress. Much like humans suffering from heatstroke in record-breaking temperatures, or animals like monkeys and marsupials experiencing heat exhaustion, coral reefs are also struggling to cope with rising ocean temperatures.


Unlike land-based heatwaves, the plight of corals often goes unnoticed. However, the signs of their distress are clear: coral bleaching. This occurs when corals expel the colorful algae living within their tissues, turning them stark white. It's a visible symptom of the ocean's deteriorating health, primarily driven by climate change. As our planet warms, the delicate balance between corals and their algal partners is disrupted, leading to more frequent and severe bleaching events.


Recent years have witnessed catastrophic global bleaching events, with 2024 marking a particularly devastating year for the Great Barrier Reef and Pacific reefs. Previous mass bleaching events in 2020 and 2014-2017 underscore the accelerating pace of this crisis. These events not only threaten marine biodiversity but also jeopardize the livelihoods of millions who depend on healthy coral reefs.




Understanding Coral Bleaching

Corals are complex organisms, a partnership between animal and algae. The coral provides a home for tiny algae called zooxanthellae, which produce food through photosynthesis. In return, corals receive nutrients. When stressed by heat or other factors, corals expel these algae, causing them to turn white. Without their colorful partners, corals become more vulnerable to disease and death, and entire reef ecosystems can collapse.



The Culprits Behind Bleaching

Climate change is the primary driver of coral bleaching. Rising sea temperatures, fueled by greenhouse gas emissions, are pushing corals to their limits. Other factors contributing to this crisis include ocean acidification, pollution, overfishing, and unsustainable tourism.

A Ray of Hope: Coral Shading

"Coral shading" is a technique being explored to mitigate the effects of coral bleaching by providing temporary relief from heat stress. The idea involves using physical structures, such as shade cloths or underwater canopies, to shield coral reefs from direct sunlight, thereby reducing water temperatures in the immediate area.


By lowering the temperature around the corals, shading can help prevent apoptosis, mediated cell death, of zooxanthellae, a mutualistic algae that live on the calcium carbonate exoskeleton of coral providing nutrients and energy through photosynthesis. Zooxanthellae also provide corals with the vibrant colors we are used to.


One caveat of shading corals is over shading and suffocating the colony of too much light and not allowing for efficient photosynthesis. Along with determining which shade cools the water temperature down to a suitable level to deter bleaching, we are also monitoring for healthy coral growth.




We picked 3 different UV light blocking shades of 50%, 70% and 90%. We built PVC structures and suspended them above coral platforms each with 3 colonies of Porites porites, Porites astreoides, and Agaricia tenuifolia. Furthermore, there is a control platform with no shade with the same species. We are using this platform as a baseline to compare our data from the other platforms with shades. Our team is going down at the same time every day to take light intensity, water temperature, water quality and coral health measurements. Over the next few months we will hopefully determine a pattern to which shade is the most efficient in providing a suitable habitat for corals.


So far, we had 1 colony bleach that’s not under the test shades. But it’s too early to tell if this behavior will spread and which shade percentage is most effective. If it does indeed work, this tactic could be a viable tool to deploy to buy the corals some time until humanity is able to solve climate change and bring temperatures back into the normal range.




Why Should We Care?

Coral reefs are often called "rainforests of the sea" due to their incredible biodiversity. They support approximately 25% of all marine life, despite covering less than 1% of the ocean floor. This includes thousands of species of fish, invertebrates, and other marine organisms that depend on reefs for food, shelter, and breeding grounds.


Beyond their ecological importance, coral reefs also provide significant economic benefits. They support fisheries that feed millions of people, protect coastlines from erosion and storm damage, and contribute to tourism industries worldwide.


Studies show even if we limited global warming to 1.5°C above pre-industrial levels, about 70-90% of coral reefs would still be at risk, with near-total loss expected if temperatures rise by 2°C or more​.


The extinction of coral reefs would have devastating consequences, not only for marine life but also for human communities that depend on them. It would lead to a decrease in fish populations, increased coastal vulnerability, and the loss of livelihoods for millions of people.

Protecting them is not just an environmental imperative but a moral one, as the consequences of inaction will be felt by future generations. Once an animal becomes extinct, there is no bringing it back. The time to act is now, before it’s too late.

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