Levels of Ocean Biodiversity Have Barely Changed for Hundreds of Millions of Years, Scientists Say

Levels of biodiversity in the world's oceans have remained virtually unchanged for hundreds of millions of years, according to a new study published in Science.

The conclusion that marine biodiversity has stayed stable over time and not mushroomed over the last 200 million years or so challenges existing assumptions that there has been a steady diversification of species, say the study's authors.

"Our paper rejects past hypotheses that marine diversity today is higher than ever before, due to sustained increases over the last 200 million years. Rather, we find that levels of diversity today are likely not that different from levels hundreds of millions of years ago," lead author Dr. Roger Close, a paleobiologist at the University of Birmingham in the U.K., told Newsweek.

"This may have implications for the way we understand modern biodiversity and conservation."

According to Close, the assumption that biodiversity levels increase at least partially stems from a methodological error—the global fossil record it hinges on is not really global. It is more fractured than the name suggests, varying in geographic reach and continuity, which leads to skewed results.

"The fact that the 'global' fossil record isn't really global hasn't been widely acknowledged before now," said Close. But new computer models able to identify patterns in regional-scale diversity have enabled Close and his team to analyze shifts in biodiversity levels across time and space from the beginning of the Cambrian Explosion, approximately 540 million years ago, to the present day.

The results suggest that global biodiversity levels did not increase in a sustained fashion for extended periods of time. Rather it remained stable. However, the team did notice differences in levels on a regional scale, with coral reefs historically displaying some of the greatest variety of species—as they do today.

"When you look at these individual animal groups, you can see fluctuations in diversity that are often substantial. But taken together, these patterns sum to one of constrained diversity," Close said in a statement.

"Some groups might benefit from the misfortune of others, but the overall levels of diversity that we see have remained fairly stable for hundreds of millions of years."

According to Close, understanding how biodiversity came to exist over deep time offers important context for today's biodiversity—as well as how it may change in the future.

This may be particularly relevant today given a number of recent studies suggesting marine biodiversity is under serious threat, from disappearing coral reefs to accelerating rates of species extinction. According to a study recently published in One Earth, more than a quarter of the world's oceans must be protected to preserve marine biodiversity.

If current trends continue, would Close expect to see notable declines of biodiversity on the fossil record or does he think it would be followed by a subsequent boom in biodiversity levels?

Close points to the Cretaceous Period 66 million years ago, when an extinction event wiped out roughly half of all plant and animal species (most notably non-avian dinosaurs). The study suggests it was followed by a dramatic shift in biodiversity levels, with an expanding roster of new species—and gastropods in particular—that took advantage of the space left behind.

"We find a rapid recovery of diversity levels after the last mass extinction 66 million years ago—in fact, to levels even higher than before (although the time resolution of our study is fairly low)," said Close. "Past work has suggested that biodiversity would recover from anthropogenic extinction within a few million years.

"So long after we're gone, biodiversity will likely bounce back to levels seen for tens to hundreds of millions of years. But it will take hundreds of thousands to millions of years, and it depends how badly we mess up the natural environment."

Correction 4/24/20, 3:30 a.m. ET: This article has been updated to correct the name Roger Close. We regret the error.

Fish swimming through coral
This file photo taken on September 22, 2014, shows fish swimming through the coral on Australia's Great Barrier Reef. According to new research, ocean biodiversity has remained relatively stable over hundreds of millions of years. Coral reefs have historically been some of the most regionally diverse environments, like they are today. WILLIAM WEST/AFP/Getty