Corals of the Caribbean: How Corals with High Genetic Diversity Survived Climate Change

Scientists from the Smithsonian Tropical Research Institute have discovered one group of corals that survived the Caribbean coral extinction between one and two million years ago continues to adapt to future climate changes because of their high genetic diversity.

Corals in the genus Orbicella are the center of Carlos Prada's research. The lead author of the study and Earl S. Tupper Post-doctoral Fellow at the Smithsonian Tropical Research Institute, Prada explained that having a lot of genetic variants is similar to buying a lot of lottery tickets. "We discovered that even small numbers of individuals in three different species of the reef-building coral genus Orbicella have quite a bit of genetic variation, and therefore, are likely to adapt to big changes in their environment."

"The implications of these findings go beyond basic science," shared Monica Medina. A research associate at STRI and the Smithsonian's National Museum of Natural History and associate professor at Pennsylvania State University, Medina said, "We can look forward to using similar approaches to predict demographic models to better manage the climate change threatened Orbicella reefs of today."

The movement of glaciers to cover much of the northern hemisphere two to 1.5 million years ago caused sea surface temperatures and number of coral species in the Caribbean to plummet. Sea levels also fell and eliminated the original shallow, near-shore habitat of even more corals.

Researchers from the Smithsonian's Bocas del Toro Research Station and Naos Molecular and Marine Laboratories gathered fossils from ancient coral reefs and used high-resolution geologic dating methods to determine their ages. After comparing the numbers of fossilized coral species at different time points, the best-represented groups in the fossil collections were species in the genus Orbicella. Genome sequencing was used to estimate current and past numbers of several Orbicella species and it was discovered that within a single individual there are two copies of their genetic material. In some instances, one copy is different than the other and is called a genetic variant.

"Apart from the species that exist today, all species of Orbicella that survived until two million years ago suddenly went extinct," wrote the authors. When a species becomes extinct, it loses more genetic variation and sometimes does not have much to work with during the recovery period. Scientists call this a genetic bottleneck. Orbicella was able to recover after the bottleneck.

"We see hope in our results that Orbicella species survived a dramatic environmental variation event," concluded Prada. "It is likely that surviving such difficult times made these coral populations more robust and able to persist under future climatic change."