According to an international team of scientists, the relationship between corals and the micro-algae that enable them to build reefs is much older and more diverse than previously thought. The study suggests that the symbiotic relationship of coral and algae probably endured untold numbers of climate change events over the course of millions of years, thus offering assurances that they can endure global warming heralded by some climatologists.
"Our research indicates that modern corals and their algal partners have been entwined with each other since the time of the dinosaurs, approximately 160 million years ago - 100 million years earlier than previously thought." Said Dr. Christian Voolstra, co-author of the study and Associate Professor of Marine Science in the Red Sea Research Center at King Abdullah University of Science and Technology. "During their long existence, they have faced severe episodes of environmental change, but thanks to their biological characteristics have managed to bounce back after each."
He said that the zooxanthellae or micro-algae live inside the cells of corals and allow them to obtain energy from sunlight and to build the massive, economically valuable reef formations upon which countless marine organisms rely for habitat. Among the two largest such reefs in the world are the Great Barrier Reef of Australia and a small barrier reef off the coast of Belize and Mexico.
Using genetic evidence that included DNA sequences, phylogenetic analyses and genome comparisons, the team calculated the micro-algae's approximate age of origin. They also used classical morphological techniques in which they compared visual characteristics of these symbionts [organisms in symbiosis] 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. Their results are published online in the scientific journal Current Biology.
"Using genetic techniques, we have developed an updated naming scheme that provides a new framework to identify different micro-algal symbionts." Said lead-author Dr. Todd LaJeunesse of Pennsylvania State University. "Accurate taxonomy [the identification and naming of species] is a critical step in any biological research. This is especially true for studies attempting to understand how the partnership between reef corals and their micro-algae, which are needed for survival and growth, may adapt to climate change."
Voolstra noted that the team has been working for close to a decade to modernize coral symbiont taxonomy in order to improve communication among scientists and advance future research on reef corals. He emphasized that discoveries like this do not change the fact that coral reefs are facing an existential threat unless action is taken to avoid climate change but the new knowledge will enhance conservation efforts.
That symbiosis goes back roughly 160 million years - about 100 million years longer than scientists had thought - according to an international research collaboration headed by John Parkinson of Oregon State and Todd LaJeunesse of Penn State. It's also more diverse than had been assumed.
"Presently, numerous algal lineages called 'clades' are lumped into just one genus," said John Parkinson, a postdoctoral scholar in Oregon State University's College of Science. "We provide evidence that the family actually consists of at least 15 genera that include hundreds and possibly thousands of species worldwide." Parkinson was one of the author of the study. The distinctions between the algae are important, he said, because some symbionts are more resilient than others to changes in the environment.
Many corals bleach, or lose their algae, when exposed to higher than usual ocean temperatures. But others are far more tolerant of heat, and some of that resilience depends on the algal species. In general corals are bleaching about 4.5 times as frequently as they did in 1980, with severe bleaching events now occurring about every six years instead of every 25 or 30 years.
"The updated naming scheme we came up with offers a clear framework to identify different symbionts," Parkinson said. "Accurate taxonomy is a critical step in any biological research and is especially true for studies attempting to understand how reef corals and their micro-algae may adapt to climate change."
The research also suggests that given their long history, coral-algal partnerships have endured numerous climate change events in their long history, meaning that at least some are likely to survive modern-day global climate change as well.
"Over all of those millions of years, partnerships have faced major hurdles and managed to bounce back," LaJeunesse said. "The fossil record shows today's reef-building corals, like the algae, arose around 160 million years ago. Finding that the origin of the symbionts corresponds to that of their hosts implies that the partnership was one of the major reasons for the diversification and success of modern corals."