GUY RAZ, HOST:

As you take in your next breath of air, think of and thank the microscopic form of sea life known as plankton. These invisible creatures make up 98 percent of the biomass of ocean life, and the oxygen they generate is vital to life on the planet. Now, over the past two and a half years, a group of scientists set out to learn more about microorganisms in the ocean. Marine biologist Chris Bowler led that expedition, and to his surprise his team discovered up to a million new species.

CHRIS BOWLER: I mean, that's sort of a reflection of ignorance of ocean life, really, particularly the microscopic world, which, you know, is difficult to study. The way that we were looking at our samples is using DNA-based methods. And these are incredibly powerful techniques now, which really permit you to really go very deep and explore a whole community of microorganisms.

RAZ: Invisible life.

BOWLER: Right. Sort of an invisible forest living out in the ocean, if you like.

RAZ: But so crucial to - not just to the ocean's survival, our survival.

BOWLER: Right. I mean, this invisible forest generates half of the oxygen generated on the planet. Every second breath that you breathe, you should thank the plankton for the oxygen you're breathing. Unbelievable.

RAZ: I know you're still in the initial phase of that research, but so far, and during that two-and-a-half-year voyage, looking at these microorganisms, were you able to determine anything about climate change and about how it's affecting those microorganisms?

BOWLER: If we want to look at the effects of climate change, we'd ideally want to sort of sit in the same place and follow changes with time, which is something that takes times to do. So by sort of understanding the plankton communities, which are associated with areas that are more or less polluted or more or less acidic, we hope that we'll get a feel for what sort of organisms prefer which kinds of conditions.

And so as the oceans change in the future, as temperatures increase, and as they acidify, we will - we hope we will be able to sort of see - predict which of those species are likely to go extinct, which ones are likely to migrate, which ones are likely to take their place and so sort of get a feel for how the ocean's going to look in 100, in 500 years' time as a consequence to climate change.

RAZ: How long before we'll have clearer answers?

BOWLER: We brought home around 27,000 samples. So it's certainly going to be at least 10 years before, I think, we've gotten to the bottom of these samples and have a very, very clear baseline of information from which we can continue in future years. But it's going to be, you know, a continual discovery process, I think.

RAZ: That's Chris Bowler. He's a marine biologist and the scientific coordinator of the Terra Oceans Expedition that found up to a million new species of life-giving microorganisms.

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RAZ: And you're listening to ALL THINGS CONSIDERED from NPR News. Transcript provided by NPR, Copyright NPR.