Ocean heatwaves trigger massive coral bleaching periods almost annually due to the climate change. Such events threaten reefs worldwide.
The corals, too, began to discharge the photosynthetic algae inside their tissue. Wasting these brownish-colored plant cells allows the coral’s white limestone to shine through, making reefs glow. Find out what researchers discovered.
The Colorful Pigments Can Protect the Corals
Researchers knew the occurrence of unusually glowing corals was related to bleaching. But why didn’t all corals turn so colorful? When the researchers tried to expose the corals to experimental heat stress, things got even odder. Instead of becoming more colorful, the corals just bleached white. However, after more investigations, they finally found an answer.
In healthy corals, the sunlight is absorbed by the photosynthetic pigments of the algae. Corals lose their algae because of the stress, and the excess light returns inside the coral tissue, reflecting the white structure. The algae inside the coral can return to normal after the bleaching event ends. But when the coral interior is lit up vividly, it can be very stressful for the algae, and the return can be delayed or stopped altogether.
The enhanced internal light levels grow the production of colorful pigments if the coral cell can still hold some of their functions during bleaching. It can also shield the coral from light damage, creating something similar to a sunscreen layer that allows the algae to come back.
Researchers utilized satellite data and reconstructed the temperature profiles for the colorful bleaching events. They found that they tend to happen after mild episodes of heat pressure. So, when corals are exposed to extreme or extended temperature highs, they tend to bleach white.
We only observe bright neon colors in bleaching events when conditions are right. Other species of the coral community can display different colors during those episodes of bleaching. The variants of colors have evolved to allow species lots of strategies to cope with light, depending on their region.
The good news is that colorful bleached corals have more chances to recover than corals that bleach white because their vivid pigments offer them protection.