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We often hear about rising sea levels. There are also chemical changes happening in the ocean. As people put more carbon dioxide up into the atmosphere, the oceans absorb more of it and that makes the water more acidic. The effects can be tough to spot in most places. But scientists say if this continues it could be a disaster for marine life. They also say there may be ways to protect plants and animals in the oceans. NPR's Christopher Joyce reports.

CHRISTOPHER JOYCE, BYLINE: There are a few places in the ocean that are naturally very acidic - seeps where carbon dioxide rises out of vents in the seafloor. These could offer a preview of the future. Marine biologist Kristy Kroeker has dived down to see those places. I talked to her about them aboard a research boat in the Pacific.

KRISTY KROEKER: It's like you're swimming through a glass of champagne where there are bubbles coming up all around you.

JOYCE: But with a shot of vinegar thrown in. And the effects of that acidity are nasty.

KROEKER: It's really striking. And it's not, I think, what people want their oceans to look like. The algae tends to overgrow just about everything so you get a more monotone, green, slimy ecosystem.

JOYCE: There's almost nothing alive. In the rest of the world's oceans, things aren't that bad yet. But even small increases in acidity are having subtle effects - on shellfish, for example.

KROEKER: It takes more energy for these animals to build their shells in more acidic conditions. These are things like oysters or muscles or snails.

JOYCE: Marine biologists are becoming somewhat obsessed with acidification and some are looking for ways to protect marine animals and plants. Here in California they found nearly ideal places to do that. The state has created them - the nation's largest network of coastal reserves. You can see why they have. In a beach in downtown Santa Cruz, volleyball players lunge across the sand courts.

UNIDENTIFIED MAN: Get up, get up, get up.

JOYCE: Tourists line up for whale watching and dive trips. And kids marvel as glistening seals surface and beg for food. More than two-thirds of Californians live within a few miles of the ocean, but all that love has also brought pollution, oil spills and overfishing. That's why the state has created 124 protected areas along its coast. Some hug the shore, some are miles out in the ocean. You can't drill or develop in any of them, and you can't fish in about half of them. Ecologist Mark Carr says they were intended to be aquatic wildernesses and fish nurseries.

MARK CARR: You're protecting the sources of young that are replenishing those populations along the coast.

JOYCE: Carr studies fish at the University of California, Santa Cruz. He says so far the network seems to be helping some species - lobster and blue rockfish, for example. But now Carr and other scientists say these protected areas are like natural laboratories where scientists can study an even bigger problem, one they'd never imagined when they created the reserves - ocean acidification. Here's why - when something affects marine life in the ocean, it's often hard for scientists to pinpoint the cause.

CARR: When they see changes in the size of fish populations, to what extent is that driven by fishing or to what extent is that driven by changes in the ocean climate?

JOYCE: If there's no fishing and fish numbers are going down then scientists know it must be something else, perhaps acidification affecting the food chain from plankton up to tuna. The value of reserves isn't lost on fishermen either. Some who first fought the idea of reserves, like Bruce Steele, now embrace them. I meet Steele at a beach near Santa Barbara. He spent 40 years scuba-diving for sea urchins in these waters.

BRUCE STEELE: You have to have some place to look where you can filter out the fishing influence, otherwise what would happen? It's so much easier to just blame us. You could just say it's just the fisherman, we're not really going to take care of these problems.

JOYCE: Scientists from the University of California, Santa Barbara have already selected a protected area for acidification research. The team has gathered in the cabin of a 55-foot research boat in the city's harbor. They're off for a four-day expedition.

JAY LUNDEN: Hi, everybody. Welcome aboard.

JOYCE: Biologist Jay Lunden outlines the trip. Today it's Santa Cruz Island, an island near the city surrounded by protected areas. Why this island? Because of the seagrasses here, also called eelgrass. They're underwater meadows and they do something very curious that's got these scientists excited. The grasses seem to be able to neutralize acidity in the water.

LUNDEN: Seagrass beds absorb CO2, and they can buffer acidification. And that's why we're going to this seagrass bed. We want to know where the seagrasses actually are.

JOYCE: If that's true, these places could become refuges for sea life trying to escape acidic water. Ninety minutes by a boat from the coast, the island is a menagerie of sea life. Team leader Gretchen Hofmann says the plants and animals here have evolved to live in this particular environment around this island. That means they're very sensitive to changes in the chemistry of seawater here. If it becomes more acidic they'll show it, like living litmus paper.

GRETCHEN HOFMANN: This isn't just some esoteric little exercise because we know that organisms are very fine tune and adapted to what they've experienced historically in the environment.

JOYCE: Once the boat is anchored near the island, the team lowers a video camera overboard looking for eelgrass. They watch from a big screen in the cabin.

HOFMANN: You want to be right above it. OK, we're now in the eelgrass bed. Oh, oh, right there. Oh, did you see that? A giant kelp fish.

JOYCE: Out on deck, Hofmann watches as other members of the team motor back and forth above the seagrass bed in the zodiac dinghy, taking water samples to check for acidity. It's slow going and wet.

HOFMANN: Zodiac science is zodiac science. How many more samples do you have left - over?

UNIDENTIFIED MAN 2: We've got to do the ten on the outside of the seagrass bed.

HOFMANN: Copy that.

JOYCE: But things perk up when the local wildlife comes over to investigate.

HOFMANN: You've got a sea lion coming in at three o'clock - over.

UNIDENTIFIED MAN 2: Copy that.

JOYCE: This is what scientists call laying the groundwork. It's slow. It will take years and thousands of measurements like these to see if these underwater meadows really can neutralize acidity in any meaningful way. But Hofmann says there's a lot at stake.

HOFMANN: You know, we want to do something to protect our backyard, our part of the ocean. And we're realizing that if these beds of eelgrass are good and that they buffer future changes in acidity, we should be protecting them or maybe even restoring them.

JOYCE: Or even planting them, something scientists are experimenting with now. In so doing, they could create refuges for fishes and plants in the sea world that could become increasingly become hostile. Safe places, where as local fishermen sometimes say, the water stays sweet. Christopher Joyce, NPR News.

MONTAGNE: And we're glad you're starting your day here with us at NPR News. We've got more ahead this morning on MORNING EDITION and later today tune in for All Things Considered. This is NPR News.

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