A U.S.-led international team of scientists says it has discovered why some coral reefs can better adapt to global warming than others.

Penn State University Assistant Professor Iliana Baums, one of the team's leaders, said discovering how corals respond to ocean warming is complicated because corals serve as hosts to algae that feed on its nitrogen wastes. Through photosynthesis, the algae then produce the carbohydrates that feed the coral. But when a rise in ocean temperature upsets the symbiosis, the coral may expel the algae in a phenomenon known as coral bleaching, which can cause the death of both algae and coral.

She said the challenge is to figure out why some corals cope with the heat stress better than others.

"We decided to focus on coral larvae because the successful dispersal and settlement of larvae is key to the survival of reefs," Baums said.

The researchers found the response of larvae to changing conditions depends upon where the parent colonies lived. Baums said she is excited by the clear evidence of local adaptations in populations that the study documented.

"Variation among populations in gene expression offers the species as a whole a better chance of survival under changing conditions," Baums said. "We might be able to screen adult populations for their ability to produce heat-resistant larvae and focus our conservation efforts on those reefs."

The study appears in the online journal PLoS One.