Half of all coral species in the Caribbean went extinct between one and two million years ago, probably due to environmental changes. Scientists at the Smithsonian Tropical Research Institute (STRI) think corals in the genus Orbicella, one of the survivors, will continue to adapt to future climate changes because of their high genetic diversity.
“Having a lot of genetic variants is like buying a lot of lottery tickets,” said lead author Carlos Prada, a Earl S Tupper Post-doctoral Fellow at STRI. “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.”
Between 3.5 to 2.5 million years ago, the numbers of coral species increased in the Caribbean. However, from 2 to 1.5 million years ago, a time when glaciers covered much of the northern hemisphere and sea surface temperatures plunged, the number of coral species in the Caribbean dropped. Sea levels fell, eliminating much of their original shallow, near-shore habitat.
“Apart from the species that exist today, all species of Orbicella that survived until two million years ago suddenly went extinct,” write the authors. When huge numbers of species die out, it makes room for other species to move in and occupy the space.
Two species that grow best in shallow water doubled in number at about the same time their sister species and competitor, the organ pipe Orbicella (O. Nancyi) disappeared.
When a species declines during an extinction event, it loses its genetic variation. Then, during the recovery period, they may not have much to work with, leading to a situation called a “genetic bottleneck.”
Orbicella recovered after the bottleneck. “It’s incredible how predictions from genetic data correlated so well with observations from the fossil and environmental record,” said Michael DeGiorgio, assistant professor of biology at Pennsylvania State University.
“It is likely that surviving such difficult times made these coral populations more robust and able to persist under future climatic change,” said Prada.