Boulay wondered if the two species differed in the way they live. She found that P. evermanni was less susceptible to bleaching than P. lobata. Bleaching occurs when the symbiotic relationship that corals share with single-celled algae breaks down as a result of an increase in water temperature. "If water temperatures continue to rise, and they surely will, coral species that succumb to bleaching more easily will die," Baums said. "So we're going to see a shift in the relative abundance of these two species."
Boulay found other important differences: P. evermanni had many genetically identical clones, which means that this species is reproducing asexually by breaking apart, although P. lobata did not. Further, the clonally reproducing P. evermanni, on average, housed many more tiny mussels that lived within the coral colonies' skeletons. The mussels poke through the surface of the colonies and form keyhole-shaped holes.
The researchers then wanted to determine the connection between P. evermanni's ability to clonally reproduce and its interactions with the mussels and other members of the reef community in the Eastern Pacific. Cortes remembered that several years ago a colleague had reported a finding that some corals are a target of biting triggerfish. "That was the missing piece," Baums said. "We realized that triggerfish were eating mussels inside the coral skeletons, and to get at the mussels the fish have to bite the coral. Then they spit the fragments out, and those fragments land on the ocean floor and grow into new colonies.
"This is what's fascinating," Baums continues. "No one has ever realized how important fish might be in helping corals reproduce, and here we have evidence that triggerfish attacks on P. evermanni result in as
|Contact: Barbara K. Kennedy|