Coral comes in a wide range of colors, from bright orange and red to pale pink and white. The exact color depends on the species of coral as well as the algae that live inside the coral’s tissues.
Quick answers
Coral can be orange, red, pink, yellow, green, blue, purple, brown, and more. The most common coral colors are orange, pink, and white.
What causes the different coral colors?
Corals are made up of hundreds to thousands of tiny coral polyps. Coral polyps are translucent animals that have symbiotic algae called zooxanthellae living inside their tissues. The zooxanthellae provide the coral with food and give them their vibrant colors. Different types of zooxanthellae give coral different colors. Some examples:
- Orange and red coral gets its color from zooxanthellae that contain orange and red pigments.
- Pink and purple coral contains zooxanthellae with fuchsia and purple pigments.
- Blue coral has zooxanthellae with blue pigments.
- Green coral hosts zooxanthellae that contain green pigments.
- Brown coral has zooxanthellae with diadinoxanthin, a carotenoid pigment that reflects brown light.
In some pale coral, the coral polyp’s white calcium carbonate skeleton shows through, giving it a washed out color. Bleached coral occurs when the zooxanthellae are expelled, so only the white skeleton remains.
What are some common orange and red coral species?
Some of the most vivid orange and red corals include:
- Fire coral – In the genus Millepora, fire corals have stinging cells and get their bright color from orange and red zooxanthellae.
- Cup coral – Species in the Tubastraea genus are vibrant orange and form cup-shaped colonies.
- Elegance coral – Catalaphyllia jardinei has brilliant orange polyps with neon green mouths.
- Torch coral – Euphyllia species produce short, tapered orange polyps.
- Sun coral – Tubastraea faulkneri colonies have round red and orange polyps that give the impression of suns.
What are some common pink and white coral species?
Some prime examples of pale pinkish-white coral species are:
- Pillar coral – Dendrogyra cylindrus forms tall cylindrical pillars that are pale pink or cream.
- Rose coral – Manicina areolata has elaborate rose-shaped polyps in pinks and whites.
- Brain coral – Species like Diploria labyrinthiformis can be pinkish-white shades with grooved surfaces resembling a brain.
- Lettuce coral – Agaricia species often look lightly mottled pink, red, and white.
- Moon coral – Favia speciosa has whirls of tentacles in pale cream and pink.
How does depth affect coral color?
Corals living at greater depths generally have less vibrant coloration than shallow water species. A few key reasons for this:
- There is less light for the zooxanthellae deeper down, so they produce fewer pigments.
- Deeper zooxanthellae adapt to mostly blue light penetration by increasing reflectance of blue light.
- Cooler temperatures at depth can limit zooxanthellae growth and pigment production.
For example, a type of brain coral called Diploria labyrinthiformis can range from reddish-orange in shallow waters to yellowish-brown at depths greater than 15 meters.
How does coral bleaching affect color?
When corals are stressed by high temperatures, ocean acidification, or pollution, they expel their zooxanthellae and lose color in a process called coral bleaching. Some bleaching effects:
- Brightly colored orange, red, and pink corals will turn bone white when every zooxanthellae is expelled.
- Pale corals will become even lighter without any zooxanthellae pigments.
- After severe bleaching, even the coral skeleton can start eroding away leaving no color at all.
If conditions improve, corals can reacquire zooxanthellae and regain their color. But prolonged bleaching can lead to coral death.
Conclusion
In summary, coral displays a huge diversity of colors based on the different pigmented algae living inside them. While orange and red are the most vibrant coral hues, the coral species and colony location significantly influence the final coloration. Coral bleaching provides perhaps the starkest example of how crucial the zooxanthellae are for coral’s coloring and survival.
Overview of Coral Colors
| Coral Color | Cause | Example Species |
|---|---|---|
| Orange | Orange zooxanthellae pigments | Cup coral, elegance coral |
| Red | Red zooxanthellae pigments | Fire coral, torch coral |
| Pink | Fuchsia zooxanthellae pigments | Rose coral, moon coral |
| White | Calcium carbonate skeleton showing through transparent polyps | Pillar coral, brain coral |
| Blue | Blue zooxanthellae pigments | Blue coral (Heliofungia actiniformis) |
| Green | Green zooxanthellae pigments | Green star polyp (Pachyclavularia violacea) |
| Brown | Carotenoid pigments | Bubble coral (Plerogyra sinuosa) |
| Purple | Purple zooxanthellae pigments | Grape coral (Alveopora spongiosa) |
This table summarizes some of the main coral color varieties, what pigments cause them, and example species. But many more colors and color combinations exist in corals due to the tremendous diversity of zooxanthellae and coral species.
The Role of Zooxanthellae in Coral Color
Here is a more in-depth look at how zooxanthellae contribute to coral coloration:
- Zooxanthellae are single-celled photosynthetic algae that live inside the coral’s tissues.
- Each coral polyp can contain thousands of individual zooxanthellae.
- The primary photosynthetic pigments are chlorophyll a, chlorophyll c2, beta-carotene, and xanthophylls.
- Secondary carotenoid pigments like peridinin, diadinoxanthin, and dinoxanthin create the vibrant oranges, reds, and browns.
- Other pigments like phycoerythrobilin and phycocyanin account for the blues and greens.
- The type and amount of pigments depends on the zooxanthellae species and environmental conditions like light and temperature.
- Corals with more zooxanthellae density and higher pigment levels appear brighter and more colorful.
By relying on the photosynthetic zooxanthellae for nutrition, corals can grow faster and build more elaborate reef structures. But this symbiosis also makes corals vulnerable when the zooxanthellae are lost due to environmental changes, leaving the coral starving and colorless.
How Lighting Affects Zooxanthellae and Coral Colors
Both the intensity and spectral quality of light affects coral coloring. Here’s how lighting impacts the symbiotic zooxanthellae:
- Brighter light spurs faster zooxanthellae photosynthesis and growth, resulting in more vibrant coral colors.
- Blue light penetrates deeper into water, so corals at greater depths adapt with more zooxanthellae photosynthetic proteins that absorb blue light.
- Longer wavelengths like red and orange don’t penetrate as far, limiting shallow-water corals to forms of chlorophyll that absorb red and orange light.
- Variations in both light quantity and quality changes the production of colorful secondary carotenoid pigments.
- Too much ultraviolet radiation can inhibit photosynthesis and cause zooxanthellae loss, fading coral color.
Careful manipulation of aquarium lighting, including using LEDs tuned to specific wavelengths, can replicate ideal lighting conditions and bring out the most intense coloration in captive corals.
How Other Factors Influence Coral Color
Along with zooxanthellae and light, other factors also impact the color of coral colonies:
- Coral species – Each species of stony coral contains different densities of different zooxanthellae strains, influencing color.
- Temperature – Warmer water promotes zooxanthellae growth and pigment production up until a bleaching threshold.
- Depth – Coral color usually becomes more muted at deeper depths with less light penetration.
- Age – Younger coral polyps tend to be lighter in color compared to older, larger polyps.
- Environment – Higher nutrients and clear water promote colorful zooxanthellae, while pollution causes fading.
Careful attention to all these factors is key to maintaining the health and color of corals in aquarium systems. Meanwhile, understanding how color relates to coral growth and stress also provides clues to the health of natural reefs.
Measuring Coral Coloration
Researchers use a few main techniques to quantitatively measure coral coloring and track changes over time:
- Coral color cards – Comparing coral colors to standardized color cards that assign numerical values.
- Photography – Analyzing high-resolution photographs with software that measures pixel hue and saturation.
- Spectrophotometry – Using sensors to record how much light is reflected from the coral at different wavelengths.
- Chromatography – Measuring the types and levels of pigments extracted from coral tissue samples.
These methods help establish normal color ranges for different corals and reveal clues like increased blue reflectance when the coral is stressed. Tracking coral color changes provides an early warning signal to intervene before mass bleaching occurs.
Maintaining Healthy Coral Coloration
To keep captive corals as colorful as possible, aquaculturists focus on providing optimal light, temperature, water conditions, and nutrients. Here are some key tips for success:
- Use LED lighting tuned to deliver balanced blue and red wavelengths for photosynthesis.
- Maintain stable water temperature around 77-84°F depending on species.
- Perform regular partial water changes and filter regularly to remove compounds that inhibit growth.
- Target low to moderate nitrate and phosphate levels to prevent algae overgrowth.
- Spot treat irritating aiptasia anemones and hydroids that compete for space and nutrients.
- Supplement feeding with microalgae, rotifers, or coral foods to support rapid zooxanthellae growth.
With close attention to coral husbandry, aquaculturists can foster colorful, rapidly growing coral colonies. Vibrant color is a key sign of health for any species of captive coral.
Conclusion
Coral displays an incredible diversity of colors, but orange and red are certainly the most common and recognizable coral hues. These sunny colors come from pigmented algae called zooxanthellae living within the coral’s tissues. Differences in zooxanthellae strains and densities give each coral species its distinctive palette of colors, ranging from neon orange to pastel pink. Coral bleaching provides the starkest view of zooxanthellae’s role, as bleached white coral has lost all its resident algae and colors. By understanding how light, temperature, nutrients and other factors affect these algal symbionts, we gain insight into keeping captive corals as vibrantly colored as they appear on the reef. With proper coral husbandry, aquaculturists can produce thriving colorful colonies. The interplay of coral and zooxanthellae highlights the intricate dependencies and partnerships that underpin functioning, healthy reef ecosystems.
