Study explores origin of coral reefs' biodiversity
Dive into the coral reefs of Southeast Asia or Australia and you’ll likely spot a wrasse. But which of the hundreds of kinds of wrasses will you see?
These fish can be 1 inch to more than 8 feet in length. They can be skinny like cigars or hefty like footballs. Some are somber-colored; others look like they’re attending a rave. Different species have their own creative feeding strategies: humphead wrasses crush shellfish; tube-lip wrasses slurp corals and cleaner wrasses act like carwashes, eating parasites and dead tissue off other sea creatures.
This spectacular diversity stems from wrasse ancestors that migrated from the prehistoric Tethys Sea to the area that now bridges the Pacific and Indian Oceans.
There, in a vast and vibrant cradle of coral reefs, they settled and steadily diversified over tens of millions of years.
Their story fits into a larger pattern. This region, the Central Indo-Pacific, has become the hot spot with the most
biodiversity in Earth’s oceans because many ancestors of today’s marine life colonized it so long ago, according to a recent paper in Proceedings of the Royal Society B.
The study emphasizes that biodiversity is a long game, and that the richness of species in the world’s oceans will not be easily replaced if it is lost to human activities.
“It has taken tens of millions of years to build the biodiversity of coral reefs, but it may take us only decades to destroy it,” said Mary Wisz, a professor at the World Mar
itime University in Sweden who was not involved in the study.
Explorers have long wondered why the Central Indo-Pacific holds such exceptional bounty, said Eliz- abeth Miller, a Ph.D. candidate studying ecology and evolutionary biology at the University of Arizona and the lead author of the paper.
Compare the experience of five minutes scuba diving in Indonesia or Australia with five minutes in the Caribbean, and the differ- ence is obvious, she said. For every species of butter- flyfish or parrotfish you spot in the Caribbean, you might see three or more species in Southeast Asia’s Coral Trian-
gle or Australia’s Great Barrier Reef.
“People say the Caribbean is a garden, whereas the Central Indo-Pacific is a jungle,” said John Wiens, a professor at the University of Arizona.
Using databases that aggregate research done by hundreds of scientists, Miller’s team categorized more than 12,000 fish species as pres- ent or absent in eight marine regions around the world.
The researchers then traced living species back in time, using an evolutionary tree, statistics and com
puter simulations to infer where their ancestors orig- inated.
Overall, the scientists found, biodiversity in a region today is highly related to the age and number of colonizations it has experi- enced. The Central Indo-Pacific is so diverse largely because many old lineages have settled there.
Not long after the dinosaurs went extinct, the Tethys Sea, which once separated
the ancient supercontinents of Laurasia and Gondwana, was the peak of biodiversity in the world’s oceans. But slowly, the continents drifted.
Around 35 million years ago, as the Tethys was closing off, the Australian and Pacific plates were colliding with continental Southeast Asia, creating an expanse of shallow ocean ideal for coral reefs. As species migrated from the Tethys (now the East Atlantic) to this area,
the hot spot of marine life shifted. Since then, the Central Indo-Pacific may also have been less strongly influenced by major extinction events than other warm regions, Miller said.