Coral reefs are one of the most colorful and diverse ecosystems on Earth. Their kaleidoscope of pinks, oranges, yellows, greens, blues, and violets have captivated humans for centuries. But of all the vibrant hues found on a reef, two colors stand out as the most iconic: orange and pink. When most people think of coral, they picture expansive reefs shimmering with both warm orange coral colonies and delicate pink corals. This begs the question – which color is more prevalent on a healthy reef? Is coral more orange or more pink?
The Science of Coral Color
The specific colors we observe in different coral species are produced by tiny algae called zooxanthellae that live symbiotically within the coral’s tissues. Zooxanthellae contain various photosynthetic pigments, mainly chlorophyll, carotenoids, and phycoerythrins. Chlorophyll produces greens, carotenoids produce yellows and oranges, and phycoerythrins produce reds and pinks.
The balance of these three pigments determines the final color we see. Corals that harbor mostly zooxanthellae with high concentrations of carotenoids will appear more orange and yellow. Meanwhile, corals with more phycoerythrin-rich zooxanthellae will skew pink and purple.
Quantifying Coral Color
Several scientific studies have attempted to quantify the prevalence of different coral colors across reef habitats. Researchers in Australia examined 65 common coral species on the Great Barrier Reef and found oranges and yellows to be the most frequent shades:
|Coral Color||Percentage of Species|
A separate study in the Red Sea categorized corals into five color groups. Orange-red shades were most frequent, exhibited by 34% of 133 surveyed reef sites. Pinks were significantly less common, found at only 13% of sites.
Researchers have also used image analysis software to quantify coral color on reefs. A study in the Philippines calculated that orange and red hues covered 34% of surveyed reefs compared to only 9% for pinks and purples.
Why Are Oranges More Common?
The predominance of orange coral colonies is likely related to the photosynthetic needs of zooxanthellae. Carotenoids not only produce orange tones, but also aid in light absorption and photoprotection for the symbiotic algae. Orange corals often harbor zooxanthellae genotypes specializing in carotenoid production and thrive under intense shallow light environments. Meanwhile, pink and purple corals with more phycoerythrin-producing zooxanthellae are more successful in deeper waters.
Additionally, orange carotenoid pigments may better shield the coral holobiont from oxidative damage. Corals with high concentrations of these pigments experience less bleaching stress and increased survivorship during thermal events.
Examples of Common Orange and Pink Corals
Here are some classic examples of prominent orange and pink coral species:
- Brain corals (Faviidae): Large, boulder-shaped corals with grooved surfaces and a yellow-orange hue.
- Elkhorn coral (Acropora palmata): Branched orange colonies with flattened antler-like fronds.
- Pillar coral (Dendrogyra cylindrus): Thick columns in hues of golden orange to brown.
- Star corals (Montastraea): Round, boulder-like corals with prominent orange radiating septa.
- Plate corals (Fungiidae): Solitary circular discs in bright yellow-oranges and tans.
- Mushroom corals (Fungiidae): Single disc-shaped corals in pastel pinks, lavenders, and mauves.
- Octocorals (Alcyonacea): Fleshy colonies with polyps on stalks in shades of pinks, purples, and reds.
- Cabbage coral (Leptopsammia pruvoti): Solitary corals shaped like smooth pink roses.
- Finger coral (Porites porites): Branches in light pinkish-grey tones.
- Clooney coral (Goniopora): Massive domes or plating formations in bright pinks, purples, and blues.
Geographic Trends in Coral Color
Research shows coral color can vary significantly based on geographic region and local reef environment:
- Coral communities in the shallower Arabian Gulf exhibit far more orange and brown shades compared to the deeper reefs of the Red Sea.
- Fringing reef zones contain higher orange coral cover relative to pinker fore-reef zones.
- Higher latitude, turbid water reefs like those off mainland Japan foster more orange short wavelength specialists.
- Corals at elevated temperatures often upregulate production of orange carotenoids.
However, broader regional patterns are difficult to discern given the immense diversity of coral species worldwide. For example, Indonesia’s coral Triangle epicenter harbors over 600 species and likely contains a wide rainbow of orange and pink corals.
Changes in Coral Color Over Time
It’s important to note that coral colonies can change in color and intensity over their lifetimes for a number of reasons:
- Bleaching – Loss of zooxanthellae results in faded white coral skeletons.
- Temperature – Warmer waters prompt production of more orange and red pigments.
- Light – Brighter light generates more orange while low light prompts pinks.
- Algal Shifts – Changes in symbiont types alter color towards their dominant pigments.
- Disease – Discoloration can occur in afflicted areas.
- Injury – Scars and wounds often appear more faded.
Thus, a reef that appears overwhelmingly orange one year may gain more pink hues over time. Anthropogenic climate change could also skew future reef color as warming and acidification impact coral physiology and symbiont communities.
Based on current scientific evidence, orange coral colonies do appear inherently more common than pink-hued species across global reef ecosystems. Exact percentages vary between specific locations, but on the whole, coral reef seascapes tend to be painted in vibrant warm shades of orange, yellow, red, and brown.
That said, pink corals still play a vital aesthetic role, providing soft rosy contrast amidst the fiery oranges. And thanks to the dynamic nature of reef systems, delicate pink and purple corals may gain increased prominence in future decades.
Coral reefs need both vibrant warm tones and pastel compliments to create their full impressionist splendor. So while orange corals may lead in numbers, the pinks add that extra dash of diversity and beauty to these underwater jungles.