Coral reefs come in a stunning array of colors, from bright pinks and oranges to deeper purples, blues, and greens. The specific color of any given coral depends on a few key factors: the coral species, its zooxanthellae, and water conditions like temperature and light exposure. While coral reefs as a whole display a rainbow of hues, most individual coral colonies tend toward shades of pink, orange, peach, or cream. The vibrant pinks and oranges stand out against the blue backdrop of the surrounding ocean.
Coral Species Determine Color
There are over 800 known species of reef-building corals around the world. Each species produces its own distinctive color and growth pattern based on its genetic makeup. For example, brain corals often appear in shades of yellow, green, or brown. The intricate mazes on their surface make them one of the most recognizable coral types. Meanwhile, star corals form in bright greens and pale pinks, with their namesake star-shaped polyps dotting the colony. Other corals like the rare blue coral (Heliopora coerulea) contain unique pigments that allow them to grow in shades of deep blue or purple.
However, the most common shades among coral species are various tones of orange and pink. Corals like the large-polyped staghorn coral (Acropora cervicornis) and elkhorn coral (Acropora palmata) are known for their antler-like branches in warm peach and orange. Sheet corals, ribbon corals, and leaf corals also typically appear in similar bright pastel orange or pink hues. The natural pinks and oranges stand out vibrantly against the darker seafloor backdrop.
Zooxanthellae Produce Color
Corals’ bright colors primarily come from their symbiotic relationship with algae called zooxanthellae. Zooxanthellae are single-celled organisms that live within the coral’s tissues. Through photosynthesis, the algae produce nutrients and oxygen to help feed the coral. In return, the coral provides shelter and carbon dioxide for the algae.
The zooxanthellae also give corals their distinctive color shades. The algae contain natural pigments such as peridinin, diadinoxanthin, and beta-carotenes. Peridinin produces shades of pinks to reddish-browns, while diadinoxanthin and beta-carotenes create vibrant yellows and oranges. By tweaking the levels of these pigments, the zooxanthellae can shift the coral’s resulting color. More yellow pigments lead to brighter orange and peach corals, while higher levels of pink peridinin result in deep pinks. Even more pigments within the coral’s tissues can modify these colors further.
Water Conditions Affect Color
The water conditions surrounding a coral reef also impact the visible colors. Warm tropical waters allow corals to thrive and zooxanthellae populations to remain stable. This enables corals to grow in intensely colored pinks, oranges, and reds. But when corals become stressed due to changes in temperature, light, or nutrients, they may expel some of their zooxanthellae. This can cause gradual paling or bleaching, shifting vibrant oranges and pinks to washed out grays or bone white.
Additionally, the water itself filters out certain wavelengths of light. Reds, oranges, and yellows tend to penetrate deeper compared to blues and violets. That means corals growing at greater depths often appear more blue, purple, or green since these wavelengths are most available. Meanwhile, shallow corals absorb more warm light leading to fiery orange and pink hues. Coral that starts orange when shallow may take on a deeper burgundy as it grows toward deeper waters.
Most Individual Corals are Pink or Orange
Given the factors above, orange and pink are the most common shades among individual coral colonies, polyps, and skeletons. The pigments produced by the zooxanthellae algae combined with coral genetics favor the bright peaches, pinks, and oranges. Brighter colors also help attract food sources toward the coral. Furthermore, certain species have evolved bright warning coloration, like the fire coral’s burnt orange tips, to advertise their dangerous sting.
Some examples of vivid orange and pink coral species include:
- Pink cauliflower coral (Plerogyra sinuosa)
- Orange cup coral (Tubastrea coccinea)
- Pink-tipped anemone (Condylactis gigantea)
- Sunset cup coral (Leptopsammia pruvoti)
- Pink large star coral (Montastraea cavernosa)
- Tube coral (Tubipora musica)
These corals contain specialized pigments, reflective proteins, and fluorescent compounds to achieve their bright orange and pink hues. Even pale corals settle into shades of peach, lavender, or beige rather than pure white. This further maximizes light absorption. Vibrant coloration occurs across coral families, shapes, and sizes, showing its evolutionary advantage.
How Coral Reefs Use Color
Viewed as a whole, coral reefs create splashes of vivid color against the blue ocean background. While individual corals are limited to shades of pink, orange, yellow, or brown, the reef as a whole contains a rainbow thanks to the diversity of species. The different growth forms and alternating colors also help break up the coral’s outline. This makes it harder for predators to spot while helping coral polyps differentiate colony boundaries.
Young corals are often brighter to stand out, attract food, and indicate recent open space for settlement. Older massive corals shift darker but retain neon-bright polyps and vivid branches at the tip. Corals also fluoresce in reds, greens, and oranges under blue light, likely using these searchlight colors to echo the blue moonlight and aid night feeding. All together, the coral reef’s color diversity helps support the survival and growth of each colony.
Conclusion
While coral reefs as a whole display a kaleidoscope of colors, individual coral colonies largely settle into shades of orange and pink. These warm, bright colors arise thanks to pigments from the coral’s zooxanthellae that absorb and reflect light. Coral species’ genetic makeup also influences coloration, leading to consistent shades within a species. Water conditions can also impact growth colors based on light availability, temperature, and runoff. When viewed up close, most healthy corals appear in fiery oranges, sunny yellows, and rosy pinks with only occasional purple, blue, or green varieties. These vivid colors suit shallow, warm reef environments and help the coral access food and light. So when it comes to a coral’s color, the most common answer is coral reefs are pink or orange. The mix creates a rainbow reef that relies on these bright, warm colors to thrive.