In the Caribbean, five of the seven seaweeds studied caused bleaching of the coral, while in the Pacific, three of eight species studied caused the effect.
The harmful chemicals affect only coral in direct contact with the seaweed, suggesting the compounds are not soluble in water, Hay noted. The effects which were measured through photographic image analysis and Pulse-Amplitude-Modulated fluorometry also varied considerably, with certain seaweeds showing stronger impacts than others.
Conducted during 2008 and 2009, the study adds new information about the decline of reefs worldwide, and reinforces the importance of maintaining a healthy ecosystem that includes enough herbivorous fish to keep seaweed under control.
"Removing the herbivorous fishes really sets up a cascade of effects," said Hay, who holds the Harry and Linda Teasely Chair in the Georgia Tech School of Biology. "The more you fish, the more seaweeds there are. The more seaweeds there are, the more damage is done to the coral. The less coral there is, the fewer fish will be recruited to an area. If there are fewer fish, the seaweeds outgrow the coral. It's a downward death spiral that may be difficult to recover from."
In earlier research, Hay and other researchers demonstrated that keeping fish away from coral reefs fuels the growth of seaweeds, and that certain fish are responsible for eating specific seaweed species. That information could help guide fisheries management by encouraging protection of fish that control the most harmful seaweeds.
"The most damaging seaweed in our study is eaten voraciously by one species of fish, and no other species will touch it," Hay said. "Now that we know that seaweeds can kill coral through these chemical means, it is even more important to understand which herbivores control which seaweeds so
|Contact: John Toon|
Georgia Institute of Technology Research News