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Bill Radke: Scientists say greenhouse gases are not only warming the planet but also making the oceans more acidic, threatening aquatic life and the livelihoods of commercial fishermen. As Marcia Lynn reports from Homer, Alaska, a group of fishermen and other mariners gathered yesterday to send out an S.O.S.

[Sound of man shouting.]

Marcia Lynn: A photographer shouts out instructions to the pilots of about a hundred fishing and recreational boats preparing to form a giant S.O.S. on Kachemak Bay.

Scientists say as more CO2 is absorbed in the ocean, the water becomes more acidic. This makes it more difficult for shellfish to grow healthy shells, and could in turn reduce populations of fish that depend on them for food, like salmon.

About half the seafood produced in the U.S. comes from Alaskan waters, and more than 50,000 people make a living from the state's fisheries. One of them is Alan Parks. He says ocean acidification is a major concern for him and his family.

Alan Parks: Basically I've been making a living off of the ocean for the past 30-some odd years. The ocean provides clothing, food and shelter for my family. I'm intimately connected with it and the health of it.

Parks helped organize the event. Boats of all sizes steamed into place to form the massive "S.O.S." A group of kayakers paddled into the center of the "O" to spell out the words "Acid Ocean." A photographer in a helicopter overheard snapped a series of pictures to record the event.

In Homer, Alaska, I'm Marcia Lynn for Marketplace.