Birdsnest coral is the common name for Seriatopora Hysterix, but few people know that the closely related green birdsnest coral is, in fact, a separate species, Seriatopora Caliendrum. This type of birdsnest coral is easily distinguishable from Hysterix by its coloration, which spans the spectrum between a creamy beige and bright, neon green. There are a number of factors that go into the green coloration, and no single one is wholly responsible for producing the bright, beautiful eerie green that this particular birdsnest coral is known best for.
One of the critical factors in allowing this Seriatopora Caliendrum produce the bright, vivid greens that many aquarium keepers prize so highly is in the nutrient content of the water. The pronounced green coloration is partially due to the presence of calcium and strontium in the water- elements that are widely available in the natural coral reefs where these creatures grow naturally. When deprived of these nutrients, the corals will turn brown as the delicate chemical balance between them and the symbiotic algae that they harbor is thrown out of equilibrium.
Another factor that goes into producing the highly attractive green coloration of this coral is the light. These coral have adapted to natural sunlight filtered through the shallow, clear waters of the reefs that they normally call home. Different waters will filter the light in various ways, producing a great variation of coloration even within nearby coral colonies. Although the corals are not photosynthetic themselves, they harbor photosynthetic algae that respond to extra frequencies beyond the spectrum of visible light in a way that helps the coral produce this bright, vivid hue.
When these corals receive the proper care or grow in a natural environment in which they can thrive, they can grow at a very quick rate and begin to spawn new colonies. They can harbor a great diversity of life within their needle-like branches, including the Hapalocarnicus Marsupialis crab, the female of which uses the corals as a semi-permanent nest when producing offspring. Research shows that these crabs prefer healthier, brighter corals when available, indicating the beige and brown ones are undergoing difficulty with their environment, largely due to the excess growth of algae that can smother the coral.