As global warming continues – and the oceans absorb most of the heat – coral fluorescing is becoming more noticeable and more frequent.
The Philippines in 2020 caused corals to fluoresce and bleach all around Palawan.
Acropora corals fluoresce due to thermal stress during a marine heatwave. San Vicente, Palawan, 2020
Acropora corals fluoresce in response to thermal stress during a marine heatwave. While previous bleaching events only occurred during El Niño warm phases, in 2020, Philippine reefs experienced mass coral bleaching during ENSO neutral conditions. Marine scientists view this as a precedent for more frequent bleaching events in the coming years. San Vicente, Palawan 2020
Acropora corals fluoresce in response to thermal stress during a marine heatwave.
These corals are part of the South Sea Reef Rehab Coral Garden, a Marine Protected Area in Daplac Cove, Palawan, Philippines. Although this image was made at noontime, the water was relatively dark as Tropical Storm Noul passed overheard. These cloudy conditions accentuated the coral's fluorescence against the dark water.
Corals produce fluorescent pigments to protect them from too much high-energy solar radiation. They glow because the fluorescent pigments absorb ultraviolet light and re-emit it as a colour with a longer wavelength, now visible to our eyes.
The other source of colour in corals is their symbiotic relationship with microscopic algae, called zooxanthellae, living in their tissue. This life-sustaining partnership powered by photosynthesis can break down if a coral experiences too much heat and ultraviolet light. If this happens, the coral bleaches and can die.
Before Tropical Storm Noul passed over this reef, the sea temperature was 32-3ºC. Many corals had turned white or were glowing otherworldly, fluorescent colours. After four days of cloudy skies and rains, the sea temperature dropped to 29-30ºC however this is still high for September and some corals were not able to recover.
Whilst previous bleaching events only occurred during El Niño warm phases, in 2020 Philippine reefs experienced mass coral fluorescing and bleaching during ENSO neutral conditions. Marine scientists see this as a precedent for more frequent bleaching events in the coming years.
South Sea Reef Rehab Coral Garden, near Boayan Island, San Vicente, Palawan.
2020
FLUORESCING
Fluorescent corals glow because they are re-emitting natural light.
Corals produce fluorescent pigments as protection from high-energy solar radiation. These pigments absorb UV light and re-emit it as a color with a longer wavelength, visible to our eyes.
Acropora corals fluoresce in response to thermal stress during a marine heatwave. While previous bleaching events only occurred during El Niño warm phases, in 2020, Philippine reefs experienced mass coral bleaching during ENSO neutral conditions. Marine scientists view this as a precedent for more frequent bleaching events in the coming years. San Vicente, Palawan 2020
Acropora corals fluoresce in response to thermal stress during a marine heatwave. While previous bleaching events only occurred during El Niño warm phases, in 2020, Philippine reefs experienced mass coral bleaching during ENSO neutral conditions. Marine scientists view this as a precedent for more frequent bleaching events in the coming years. San Vicente, Palawan 2020
SYMBIOSIS
The other source of colour in corals is their symbiotic relationship with microscopic algae, called zooxanthellae, living in their tissue. This life-sustaining partnership powered by photosynthesis can break down if a coral experiences too much heat and ultraviolet light. If this happens, the coral bleaches and can die.
An area of severely bleached corals in the South Sea Reef Rehab Coral Garden. The sea temperature remains above 30°C, even as Tropical Storm Noul passes overhead. 2020
Whilst previous bleaching events only occurred during El Niño warm phases, in 2020 Philippine reefs experienced mass coral fluorescing and bleaching during ENSO neutral conditions. Marine scientists see this as a precedent for more frequent bleaching events in the coming years.
A of crown-of-thorns starfish (Acanthaster planci) on a coral in Daracoton Bay. Palawan 2021.
CROWN-OF-THORNS STARFISH
Crown-of-thorns starfish eat live coral polyps and, in large numbers, can strip a reef of 90% of living coral tissue.
An outbreak of crown-of-thorns starfish (Acanthaster planci) on a reef near Linapacan Island, 2019.
The bright white exoskeleton of a coral that has been devoured by a crown-of-thorns starfish (Acanthaster planci). Near Sibaltan, Palawan 2022.
Although they are a natural part of coral reef ecosystems, these starfish usually occur in low numbers. Scientists consider it an outbreak when there are more than 30 individuals per hectare.
A of crown-of-thorns starfish (Acanthaster planci) on a coral in Daracoton Bay. Palawan 2021.
Crown-of-thorns starfish are the most fertile invertebrates in the world - when a female spawns, she releases 20 million eggs. The typical survival rate for her young is just 0.00001%, but when conditions change, such as water quality and temperature, or when natural predators are absent, populations can soar.
A teams of divers inject crown-of-thorns starfish with vinegar to control an outbreak on a coral reef in northeast Palawan.
“Warming waters and pollution increase the reproduction of crown-of-thorns starfish,” says Sana Schifferer of Dive Sibaltan. “While overfishing, collection of triton shells and illegal fishing methods means they have fewer natural predators. With hardly any protection in place on the east coast, we try our best to support the health and survival of coral reefs by monitoring and controlling COT outbreaks – we hope to preserve the delicate ecosystem of the reef for generations to come."
An outbreak of coral-eating crown-of-thorns starfish (Acanthaster planci) on a reef near Linapacan, northeastern Palawan.
