Coral-algae partnerships have gone through many climate changes in their long history, and at least some are likely to survive today's global warming, suggests an international team of scientists.
The team's conclusion is based on the recognition that the relationship between coral and the mutualistic microalgae that enables them to build reefs is much older and more diverse than previously thought.
"Earlier estimates put the initiation of these symbiotic relationships at 50 to 65 million years ago," said Todd LaJeunesse, Associate Professor of Biology, Penn State. "Our research shows that modern coral and its algae partners have been intertwined for a long time ̵
According to LaJunesse, the microalgae, which are usually called Zooxanthellae, are the family of dinoflagellates Symbioidiaceae cells of corals that allow them to extract energy from sunlight and build the massive, economically valuable reef formations where countless marine organisms live as a habitat.
"The fossil record shows that today's reef-building corals have exploded in diversity by 160 million years," said LaJunesse. "If one realizes that the origin of the algae symbionts corresponds to a large increase in the abundance and diversity of reef-building corals, then the partnership with Symbiodiniaceae is one of the main reasons for the success of modern corals."
The team used genetic evidence-including DNA sequences, phylogenetic analysis, and genome analysis-to calculate the approximate age of the microalgae. They also used classical morphological techniques in which they compared the visual properties of these symbionts with light and electron microscopy, computer modeling, and other methods to find out that the algal family is not only older, but also much more diverse than previously thought. The results appear online today (Aug. 9) in Current Biology .
"At present, numerous algal lines, the so-called Claden, are grouped in just one genus," said John Parkinson, a postdoctoral fellow, Oregon State University. "Using genetic techniques, we provide evidence that the family actually includes at least 15 genera, including hundreds and possibly thousands of species worldwide."
This is important, he explained, because some microalgae symbionts have properties that make them more resistant to environmental changes than other symbionts.
"The updated naming scheme provides a clear framework for identifying various symbionts," says Parkinson. "Accurate taxonomy (identification and naming of species) is a critical step in any biological research, especially in studies that seek to understand how the partnership between reef corals and their microalgae needed for survival and growth For example, if many corals are exposed to high temperatures, they lose their symbiotic algae and die off, others are much more tolerant of heat, and part of that resilience is due to the type of algae they have. " Corals contain dense populations of round, golden brown microalgae, commonly referred to as zooxanthellae. A typical coral will have one to several million symbiont cells in a tissue area the size of a thumbnail. Credit: Todd C. LaJeunesse
Parkinson noted that the team has been working to modernize the coral symbiont taxonomy for nearly a decade to improve communication among scientists and advance future research on reef corals
"So far "Studies on the physiology and ecology of these algae tried to compare apples to apples," said Parkinson. "Considering how different some of them are, we now see that we've often compared apples to oranges, and these changes will help researchers think more about the comparisons they make in experiments."