Be cautious of yellow Acropora
During a recent El Nino-driven coral bleaching event, many staghorn corals lost their normal pigmentation and turned bright yellow. Due to high water temperatures (30-36 deg C), entire coral reefs bleach during summer periods. This occurs because reef-building corals expel their symbiotic algae (known as zooxanthellae), which fall apart when seawater becomes too warm. Corals can survive only temporarily in a bleached state, as they no longer obtain nutrients from their zooxanthellae.
When staghorn corals bleach, they sometimes fluoresce a bright yellow colour, as seen on several reefs this year. This may help the coral to defend itself against damaging ultraviolet radiation from the sun. This phenomenon lasts for several days, after which the coral usually dies.
Should you encounter such a bright yellow Acropora at your local fish store, be sure to ask your vendor if this is a recently imported specimen. If it is, it may not last very long.
All images copyright XL Catlin Seaview Survey. See more pictures at http://www.globalcoralbleaching.org/.