Coral comes in a vibrant array of colors, from bright reds and oranges to pale pinks and purples. However, despite its common name, coral isn’t always pink. The actual color of coral depends on several factors.
What Causes Coral to be Pink?
Coral gets its bright coloration from tiny algae called zooxanthellae that live symbiotically within the coral’s tissues. The zooxanthellae provide the coral with food and oxygen through photosynthesis. In return, the coral provides the algae with nutrients, carbon dioxide, and shelter.
The zooxanthellae contain pigments such as peridinin, diadinoxanthin, chlorophyll a, chlorophyll c2, and beta carotene. These pigments are what give the coral its vibrant coloration. The most common pink and reddish shades in coral come from the presence of phycoerythrin, a pink or reddish pigment, in the zooxanthellae.
When the pigments combine in high densities, they can create bright pinks and reds. Lower densities lead to more pale pinkish hues. The specific color depends on the coral species, water conditions like temperature and light exposure, and relative concentrations of each pigment.
When Is Coral Not Pink?
While pink is perhaps the color most associated with coral, coral reefs actually contain a wide diversity of colors. Here are some examples of when coral is not pink:
- Coral bleaching – When corals become stressed by changes in temperature, light, or nutrients, they expel their zooxanthellae. This causes them to turn white and appear “bleached.”
- Deep water coral – Corals living in deeper, colder waters tend to host different zooxanthellae types that lend purple, blue, gray, and green hues.
- Highly pigmented zooxanthellae – In shallow reef environments, some coral species contain types of zooxanthellae that produce more green and brown pigments, creating coral colonies in earthy tones.
- Blue coral – A type of coral in the genus Heliopora contains a brilliant blue pigment alongside the chlorophyll. This lends the coral a distinctive blue color.
- Fluorescent proteins – Some coral species produce fluorescent proteins that lend neon greens, reds, and oranges under certain light wavelengths.
The natural color diversity of coral reefs is part of what makes them such a visually stunning underwater environment.
What Factors Influence Coral Color?
Many factors influence the color displayed by corals. Here are some of the major ones:
- Zooxanthellae genotype – The species and genetic strains of the symbiotic algae play a major role in determining pigment production and coral coloration.
- Light exposure – Corals in high light environments tend to have more concentrated zooxanthellae populations and more vibrant colors. Shaded corals are often lighter and more pastel toned.
- Water depth – Light attenuates (fades) quickly underwater. In deeper waters, corals take on darker purple and green hues to better capture the filtered sunlight.
- Water quality – Sedimentation and pollution can impact coral color by allowing more green and brown algae to colonize the coral.
- Temperature – Warmer water temperatures speed up the metabolic rates of the coral and algae, often increasing pigment production.
- Age – Younger corals tend to be lighter in color compared to their older counterparts.
- Health – Bleaching and disease can drastically alter a coral’s color by removing or changing the zooxanthellae population.
Coral coloration is the result of a complex interaction between these different factors and the coral’s genetics. Even neighboring colonies of the same species can exhibit very different colors based on their specific conditions.
How Does Coral Color Help the Reef Ecosystem?
The bright pinks, reds, and other colors produced by coral serve some key functions:
- Aid in photosynthesis – The pigments help absorb specific wavelengths of light to power the zooxanthellae’s photosynthesis.
- Camouflage – The colors help conceal the coral from predators.
- Attract pollinators – The vibrant colors draw in fish that aid in coral reproduction.
- Protect from UV light – Pigments help absorb and dissipate damaging ultraviolet radiation.
- Species recognition – Distinct color patterns help coral larvae identify appropriate settling sites.
- Temperature regulation – Darker pigments help coral absorb and distribute heat.
Researchers continue working to fully understand the adaptive benefits of the striking color diversity on coral reefs. However, it is clear that color plays many important roles in the biology and ecology of corals.
Famous Pink and Red Coral Reefs
While coral reefs around the world contain a rainbow of colors, certain reefs are particularly renowned for their vibrant pink and red corals. Here are a few examples:
- Northern Red Sea (Eilat, Israel) – Coral reefs along Israel’s Red Sea coastline are dominated by brilliant red corals. Acropora and Porites coral account for much of the red hue.
- Great Barrier Reef (Australia) – Pink soft corals of the Dendronepthya genus color entire bommies and reef faces, alongside pink and red hard corals.
- Flower Garden Banks (Gulf of Mexico) – These coral reefs off the coasts of Texas and Louisiana are covered in colorful coral groves, especially vibrant pink and red sea fans.
- Verde Island (Philippines) – This island within the Verde Island Passage Marine Corridor displays a diversity of pink and red corals, including bubble, boulder, and encrusting species.
- Chagos Archipelago (Indian Ocean) – These remote atolls contain coral colonies and reefs in vivid shades of orange, pink, and red, especially around shallower lagoon reefs.
The aesthetic beauty of these pink underwater wonderlands makes them popular scuba diving and snorkeling destinations for people around the world. Their beauty is also a reminder of why it is so important to protect coral reef ecosystems.
Threats to Coral Reefs and their Pink Colors
Many threats put coral reefs and their colorful displays at risk, including:
- Rising ocean temperatures leading to mass bleaching events
- Ocean acidification making it harder for corals to build their skeletons
- Destructive fishing practices like cyanide and blast fishing
- Pollution and sedimentation from coastal development
- Physical damage from boat anchors, divers, storms etc.
- Invasive species outcompeting and damaging native corals
All of these stressors can cause the coral to lose its zooxanthellae and vibrant coloration. Some impacts are more direct, like cyanide fishing which extracts colorful corals for the aquarium trade. Other threats like warming oceans act more chronically to degrade reef environments over time.
Conservation efforts aim to reduce local threats like pollution and overfishing, while climate change mitigation targets the global drivers of mass bleaching. Protecting these fragile underwater ecosystems preserves both their ecological integrity and their aesthetic beauty for future generations.
Conclusion
While pink has become the signature color of coral, reefs actually contain a stunning diversity of colors dictated by a blend of environmental factors and coral genetics. The prevalence of pink comes from the specific types of algal pigments living within the coral polyps. But blue, green, purple, orange and more can all be common under the right conditions. These colors serve important biological functions, while also creating some of the most visually spectacular ocean vistas on the planet. However, coral reefs face many threats that put their colorful future at risk. Protecting these fragile underwater ecosystems is key to preserving both their ecological richness and their aesthetic wonder for generations to come.