Purple Acropora coral species have often been a subject of debate regarding the specific circumstances that allow them to develop their particular hues, as well as the reason for doing so.
While purple pigments, like pink and blue ones, are mainly considered to add a layer of protection between the coral and the excessive UV lights penetrating the ocean surface and being potentially dangerous for the corals’ survival, a variety of other factors also seem to have an impact on why the purple pigments are developed – including geographical location, depth and water content.
Acropora colonies that use purple pigments may vary depending on their species’ characteristics such as size and resilience, however, most of them will require a stable environment with temperatures that rarely fluctuate more than 5-6 degrees on average (while remaining in the 70-80 F range) and stable quantities of magnesium, water pH and trace elements.
A good example that falls in this category is the rare, purple colored Cerealis Acropora coral. Commonly found in areas such as Fiji, Indonesia, Australia and southern China, this coral is a bright purple color, ranging between 1 and 7 inches in height, and can normally be found on upper reef slopes, closer to the surface where fewer of the Sun’s UV rays are filtered by the ocean’s water.
Although it’s safe to say that purple Acropora species in general use their color to protect against dangerous levels of UV radiation, it may also be important to note exactly which types of UV light levels actually need to be reduced.
There are three essential varieties of UV radiation, known as UV-A, UV-B and UV-C. While the latter is not of consequence, since it rarely if ever penetrates the atmosphere of the Earth, UV-A and UV-B rays can constitute a destructive factor for coral DNA.
Corals such as the purple Cerealis species mentioned earlier develop various shades of purple pigment to protect against higher or lower levels of these UV rays. Deeper areas will generally filter these rays and require less protection. As a result, corals that use high frequency colors such as purple and pink will generally come from a shallow area where the need to protect against a higher amount of UV-A or UV-B sunrays is more pronounced.
It is important to note that corals such as purple Acropora may change color depending on climate or water level changes, and may even lose some of their pigments; however, this is not always cause for concern, since the coral may simply adapt its pigmentation in accordance with the newly altered amount of UV rays it needs to fend off or attract.