Tropical reefs can change their composition from vibrant corals to underwater fields of seaweed. Now, researchers have determined that, surprisingly, these communities can exist under the same conditions and the findings may have broad implications for reef conservation. Macroalgae, or seaweed, often outcompetes coral on reefs unless it's kept in check by herbivores such as algae-eating fish. The amount of herbivory on a reef is a major factor in determining whether the site will become a coral reef or a seaweed field. Reefs in many parts of the world have switched from coral to seaweed, and the researchers are trying to determine why. One possibility is that the environment has changed in a way that favors seaweed, and that even if the seaweed disappears, the new conditions may no longer suit coral. The researchers wanted to determine whether there might be another explanation, one with other implications for coral reef management. They explored whether a coral community and a seaweed community could exist in the same conditions by manipulating the amount of herbivory on a reef. The findings suggest that even a seemingly healthy ecosystem could be vulnerable to dramatic shifts. A large enough change could alter the entire ecosystem.
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