Attack of the Killer Seaweed
Top photo is of a rarely fished reef. Bottom photo after seaweed begins its invasion. Photo Credit: E. Hunter Hay (top); I. P. Markham (bottom)
In order to test this theory, researchers threaded eight different Fijian seaweeds through heads of coral including Acropora millepora. The results confirmed their suspicions. Within two weeks the coral tissue began to discolor and die where the seaweeds touched the corals. Control "seaweed" made out of plastic had no effect. This research was just reported in Proceedings of the National Academy of Sciences in an article titled Macroalgal terpenes function as allelopathic agents against reef corals.
When the killer seaweeds were ground up and analyzed, the researchers found the culprit: terpenes. Terpenes are a class of compounds that some seaweeds use to keep herbivorous fish from feeding on them as it makes them sick. One species of seaweed was found to be particular nasty: turtle weed (Chlorodesmis fastigiata). The majority of marine herbivores will not touch it - all except one: a certain species of rabbitfish. This highly specific appetite highlights the need for judicious fishing practices where these and other species of seaweed exist.
The paper in its entirity can be read at the following link: Macroalgal terpenes function as allelopathic agents against reef corals
Interestingly enough, turtle weed seaweed regularly turns up in the aquarium trade so be on the lookout.