Competition may have a high cost for at least one species of tropical seaweed. Researchers examining the chemical warfare taking place on Fijian coral reefs have found that one species of seaweed increases its production of noxious（有害的） anti-coral compounds when placed into contact with reef-building corals. But as it competes chemically with the corals, the seaweed grows more slowly and becomes more attractive to herbivorous（食草的） fish, which boost their consumption of the skirmishing（冲突，争执） seaweed by 80 percent.

This appears to be the first demonstration that seaweeds can boost their chemical defenses in response to competition with corals. However, determining whether such responses are common or rare awaits additional studies with a broader range of seaweeds and corals.

The research, sponsored by the National Science Foundation and the National Institutes of Health, was published January 8, 2014, in the journal Proceedings of the Royal Society B.

"The important takeaway is that competition between corals and seaweeds can cause dramatic changes in seaweed physiology, both in terms of their growth and their defense," said Douglas Rasher, who was a graduate student at the Georgia Institute of Technology when the research was conducted. "These changes have potentially cascading effects（层叠效应） throughout the rest of the reef community."

Rasher, now a postdoctoral research associate at the Darling Marine Center at the University of Maine, conducted the research in collaboration with Mark Hay, a professor in the Georgia Tech School of Biology. Hay and Rasher have used coral reefs as field laboratories, studying the chemical signaling that occurs during coral-seaweed competition, and evaluating how herbivorous fish affect the interactions -- and long-term health of reefs.

"We previously found that chemical warfare is fairly common among seaweeds and corals, and that several seaweed species are particularly harmful to corals," Rasher said. "This research explored the degree to which seaweed allelopathy（植化相克） -- chemical warfare -- is dynamic, how it changes in response to competition, and also whether competition changes the efficacy of other seaweed defenses used against herbivores."

The findings may also challenge the popular notion that plants cannot change rapidly and strategically in response to their environments.

"We tend to think of plants as being fixed in their behavior," said Hay. "In fact, plants such as these seaweeds assess their environment continuously, altering biochemically what they are doing as they compete with the coral. These algae somehow sense what is happening and respond accordingly. They may appear passive, but they are really the tricky chemical assassins of coral reefs."