Why are Corals Bright Colors?

There are a couple of factors affecting the color of coral. The first, and most relevant, is zooxanthellae algae. The body of a coral polyp is clear, and zooxanthellae algae are pigment cells that take up residence inside the coral's tissue. It's an innate mixture of these cells that give coral its generous display of color. Several million zooxanthellae can inhabit a single square inch of coral. Another factor that distinguishes coral color is light. With the help of the sun, zooxanthellae cells release chlorophyll by the process of photosynthesis. The coral's color is then determined by how much chlorophyll is released, as well as the amount of available light.

Unless you're a marine aquarists, you will probably never have a use for the Kelvin rating, or K rating, scale. For coral reef sustainability, the K rating system is essential. The K rating scale measures the mixture of light responsible for the color of the coral. For coral, a lower K rating is indicative of warm colors including red, yellow and orange. Higher K rating for coral represents cooler colors, such as green, blue and purple. A zero degree K rating is described as the blackest-black, and 6,500-degree K rating denotes the appearance of every color in the spectrum.

Scientific research has determined that colors administer protection for coral against the damaging effects of UV rays. Coral colors are also responsible for attracting mates; the stronger the color, the healthier the coral, the more attractive to a potential mate. When the zooxanthellae cells convert light to chlorophyll, the biological process manufactures a life-giving supply of oxygen. The brighter the color of the coral, the more oxygen is being produced. Corals can decrease or increase the chlorophyll production from the zooxanthellae cells, depending on environmental requirements.

Corals can manipulate the zooxanthellae cells in response to light. Only recently have we begun to comprehend the relationship between color-producing light and how it appears at different depths. Wavelengths of light become diluted the deeper down they have to travel. UV light rays are naturally filtered out by water in deeper oceanic regions. That's why shallow water reefs are bright with color and deeper terrain, of an identical nature, appear gray. The color for coral is a cloaking device against UV rays and is not necessary for deeper waters.