Evolution Diary

Earth’s richest concentrations of marine life have shifted over time, cropping up where tectonic plates collide and the climate is friendliest to life, new research suggests.

Today, seas surrounding Indonesia are a hotbed for marine life. But eons ago, the Mediterranean and the Arabian seas were just as rich, scientists report in tomorrow’s issue of the journal Science.

In their study, researchers compared genetic data with fossil records to discover at least three marine hot spots in the past 50 million years. The zones have migrated over time, so that almost half Earth’s surface has hosted them at various periods.

“There are always hot spots, but they are always moving,” said Willem Renema, a geologist at the National Museum of Natural History in the Netherlands, who led the study.

“[Hot spots] are dynamic entities. You can predict the location by looking at climate and tectonics.”

Warm, Shallow Seas

Renema and his colleagues launched their investigation to explain rich veins in the marine fossil record.

Climate alone wasn’t an exact match, Renema said: “The areas that are most diverse are not the warmest areas.”

But when climate was considered alongside large-scale geologic processes, the fossil and genetic markers of marine biodiversity synched up.

Hot Spot Life Cycles

A present-day hot spot for marine life is the “coral triangle,” a border area between the Indian and West Pacific oceans that is generally defined to include the coastal waters of Malaysia, the Philippines, and Papua New Guinea.

Besides some of the most abundant—and most diverse—coral reefs in the world, the region supports mangroves, sea grasses, algae, mollusks, arthropods, fish, and other marine species in unmatched concentrations.

Scientists behind the new study say a single hot spot can last millions of years, and that the coral triangle hot spot is much older than previously thought, stretching as far back as the Miocene epoch, which lasted from 23 to 5 million years ago.

But hot spots don’t last forever, and Earth’s geology has much to do with it, the team says.

As tectonic plates vie for position, one edge eventually becomes subducted, or submersed, beneath the other. The resulting uplift can produce new islands and mountains.

But during this process, nearby terrain tends to normalize, making habitat less diverse. As a result, species that depend on diverse terrain must migrate or die out.

“Usually if there are mass extinctions, they’re more severe when you are in that second phase of the hot spot cycle,” Renema said.

The new study suggests that species diversity peaks not necessarily where tectonic plates collide head-on, but at places where the meeting is messy and shallow seas of varying depths form.

As tectonic plates vie for position, one edge eventually moves beneath the other. Many millions of years later, the resulting uplift can produce new islands and mountains.

Following Hot Spots

David Jablonski, a paleontologist at the University of Chicago, described the researchers had a “really interesting hypothesis.”

He said it’s the first comprehensive presentation of an idea— that plate tectonics generate biodiversity—that first emerged in the 1980s.

Jablonski says it remains to be seen whether the abundance of marine species found today in the coral triangle has truly been hopping the globe or is in a process of contracting, with the West Pacific as a sort of last holdout.

Renema, the lead study author, concedes that more work needs to be done to track diversity hot spots more closely over time.

“We have this idea,” he said, “And now we can test it.”

Story from National Geographic