Coral reefs aren't just beautiful and rich in species. They also have long served as an evolutionary wellspring for countless types of marine life, even groups such as clams and snails that researchers thought had originated in shallow coastal waters. That's the conclusion of a new examination of the fossil record, and the findings reinforce the idea that evolutionary potential is linked to the environment.
Coral reefs are well-known hot spots for biodiversity, but scientists have assumed that many types of reef-dwelling animals had migrated from other ecosystems, such as shallow coastal waters. Paleontologist and lead author Wolfgang Kiessling of the Museum für Naturkunde in Berlin initially shared that assumption. But spurred by older studies of reefs and hints from the genetics of fishes, he took a closer look.
In 2000, Kiessling and two colleagues began to study fossils of sea-bottom-dwelling animals. Poring over the scientific literature and contributing field results of their own, they compiled records of organisms from around the world and dating back 540 million years--most of the history of multicellular life. "We thought that only an all-embracing study would answer our question [of whether] reefs are general cradles of evolution," he says.
The trio determined the environment where 6615 genera of marine species originated, based on where the fossils first appeared. In tomorrow's issue of Science, the researchers reveal  that 1426 of the genera originated in reef environments, nearly 50% more than in shallow-water environments. In addition, Kiessling says, reefs were found to contribute diversity to other habitats, because members of genera that originated in reef systems migrated away. "We were surprised to see how large the cradle effect really is."
"It's an intriguing and important paper," says paleontologist Richard Aronson of the Florida Institute of Technology in Melbourne. "The implication," he says, "is if modern reefs continue to degrade, that could have long-term evolutionary consequences for other ecosystems by cutting off the supply of new biodiversity."