An ailment that causes pink-blue spots to appear in the tissues of stony corals could be a marker of stress.
The condition, which has been named pink-blue spot syndrome (PBSS), affects the small polyped stony coral Acropora eurystoma in the Red Sea and is thought to be a locally-induced syndrome rather than a disease in its own right.
Bongiorni and Rinkevich from the Department of Marine Science at Italy's Polytechnic of Marche studied Acropora eurystoma in front of the Steinitz Marine Laboratory in Eilat and found that many of the corals were suffering from the condition.
In some of the colonies all of the individuals were suffering from PBSS so they labelled the corals and monitored what happened to them over the coming year.
The experts found that the spots formed anywhere on the corals where foreign biological matter, such as encrusting algae, touched the corals or in places where they were wounded or touched other corals.
The spots are produced by a compound belonging to the pocilloporin family, which usually gives poritid and acroporid corals their vibrant colours.
PBSS is believed to be triggered by restricted environment and local biological stress conditions, and can even be triggered in healthy corals by "bandaging" sections of their branches with plastic strips.
For more details see the paper: Bongiorni L and B Rinkevich (2005) - The pink-blue spot syndrome in Acropora eurystoma (Eilat, Red Sea): a possible marker of stress. Zoology (Jena): 2005; 108(3): 247-56.