Corals reefs could survive global warming

There may be hope for marine reefs to survive modern-day global warming, say scientists who have found that coral-algal partnerships have endured numerous climate change events since the age of dinosaurs.

The relationship between corals and the mutualistic micro-algae that enable them to build reefs is considerably older and more diverse than previously assumed, according to a study published in the journal Current Biology.

"Past estimates placed the initiation of these symbiotic relationships at 50 to 65 million years ago," said Todd LaJeunesse, an associate professor at Pennsylvania State University in the US.

"Our research indicates that modern corals and their algal partners have been entwined with each other for much longer - since the time of the dinosaurs, approximately 160 million years ago," said LaJeunesse.

"During their long existence, they have faced severe episodes of environmental change, but have managed to bounce back after each one," he said.

The micro-algae, commonly called zooxanthellae, live inside the cells of corals, allowing them to acquire energy from sunlight and to build the massive, economically valuable reef formations upon which countless marine organisms rely for habitat.

"The fossil record shows that today's reef-building corals exploded in diversity around 160 million years ago," said LaJeunesse.

"Finding that the origin of the algal symbionts corresponds to major increases in the abundance and diversity of reef-building corals implies that the partnership with Symbiodiniaceae was one of the major reasons for the success of modern corals," he said.

The team used genetic evidence - including DNA sequences, phylogenetic analyses and genome comparisons - to calculate the micro-algae's approximate age of origin.

They also used classical morphological techniques in which they compared visual characteristics of these symbionts using light and electron microscopy, along with computer modeling and other methods, to discover that in addition to being older, the algae family is far more diverse than previously perceived.

"Presently, numerous algal lineages, called clades, are lumped into just one genus," said John Parkinson, postdoctoral researcher, Oregon State University in the US.

"Using genetic techniques, we provide evidence that the family actually comprises at least 15 genera, including hundreds and possibly thousands of species worldwide," said Parkinson.

This is important because some micro-algal symbionts have characteristics that make them more resilient to changes in the environment than other symbionts.