BAR HARBOR MAINE — Each summer, our family visits this part of the New England coast, and each year I am reminded of the elemental connections humans share with the oceans.

This summer, though, brought a deeper awareness of the dramatic changes humans are bringing to our seas.

On a cool evening soon after arriving in Bar Harbor we visited the Mount Desert Island Biological Institute for a screening of Barbara Ettinger and Sven Huseby's eye-opening film, "A Sea Change: Imagine a World Without Fish."

The documentary is about a boy, his grandfather, tiny angel-like pteropod zooplankton, and how human-generated carbon dioxide (CO2) emissions are acidifying our oceans — threatening the very foundation of the marine food web.

After the film, Ettinger and Huseby agreed to an interview, and the next morning my son and I joined them on the porch of their small hotel overlooking Frenchman Bay.

The Maine shore attracts millions of tourists each year. They come to sail, hike and eat seafood, and to take and paint pictures. In the process they provide crucial support for local communities. But beyond such economic, recreational and aesthetic benefits, oceans also feed us.

More than 2 1/2 billion people in the world depend on fish for at least 20 percent of the protein they consume, and more than 200 million jobs are related to fisheries. As a result, more than 75 percent of marine fisheries are now being fished at, or beyond, maximum capacity.

Still, we have taken food from the oceans for so long, it's difficult to imagine there not being enough to go round.

Now, though, as Ettinger and Huseby note in their film's tag line, it is time to imagine a world without fish.

"A Sea Change" is equal parts captivating and troubling. It relies on top scientists to explain ocean acidification, but it is held together and leavened by Huseby, a retired educator, as the protaganist — and his grandson, Elias, a youngster whose dialog is reason enough to see the film.

Similar to "An Inconvenient Truth," Al Gore's documentary, "A Sea Change" uses stunning photography to remind us of our planet's breathtaking vistas. But where Gore's film stumbles with misstatements and a topic so broad it overwhelms, "A Sea Change" remains focused on the impact atmospheric CO2 is wreaking on our oceans.

"We wanted to be able to answer questions from all perspectives, so we sat down and said, 'OK, what are the questions that people are going to want to have answered if you're an artist, an economist, a scientist or a lay person?' Then we began to do research on who would be the most authentic voices for each of them," Ettinger explained during our talk.

As well as scientists, those voices include entrepreneurs and artists.

"Maya Lin, for example, we knew was working on a project, titled 'Missing,' about extinct species and species going extinct, and we thought, 'this is perfect' — and indeed it was," said Ettinger. "Talking to her about her whole sense of why people don't think about what's under the ocean was fascinating. What you don't see you pollute, she says."

Lin, 49, became well known in the United States when, at age 21, she won the competition to design the Vietnam Veterans Memorial in Washington, D.C.

"Lin comes up with this imagery that we felt would grab people's imaginations and their hearts, and it would stick in their minds and then they would become really concerned," Ettinger said.

The problem, in short, is this: As we burn more and more fossil fuels, such as coal and oil, CO2 in the Earth's atmosphere is increasing; in turn, the oceans are absorbing more and more carbon, causing their acidification.

"Carbonic acid lowers the natural pH [alkalinity] of our oceans. That decreases the available calcium carbonate that is essential for the formation of bones in fish, shells on crustaceans and reef material from corals. For example, we are now seeing early signs of damage to pteropods [zooplankton] which are the essential food of juvenile salmon.

"The effects of the addition of CO2 to the ocean ripples across many species, including humans who rely on the sea for both sustenance and economic survival," explains the filmmakers' Web site.

Ettinger and Huseby are the first to make a full-length film about ocean acidification, but concern about it has been percolating among scientists for years. The pair first learned about the issue in November 2006, when they read Elizabeth Kolbert's article, "The Darkening Sea," in The New Yorker magazine. This set them off on a 2 1/2-year whirlwind of research, interviews and filming.

Governments, too, are beginning to recognize the looming crisis.

"The oceans have absorbed about 50 percent of the CO2 released from the burning of fossil fuels, resulting in chemical reactions that lower ocean pH. This has caused an increase in (acidity of the oceans) of about 30 percent since the start of the industrial age," explains the Web site of the U.S. government's National Oceanic and Atmosphere Administration (NOAA).

"A growing number of studies have demonstrated adverse impacts on marine organisms, including: The rate at which reef-building corals produce their skeletons decreases; the ability of marine algae and free-swimming zooplankton to maintain protective shells is reduced; and, the survival of larval marine species, including commercial fish and shellfish, is reduced," notes the NOAA Web site.

"Marine plankton is a vital food source for many marine species and their decline could have serious consequences for the marine food web," adds NOAA.

For Huseby, the film is as much about the planet as it is about moral justice.

"I think we have an obligation to those that follow. It is incumbent on us as we learn more to make sure that our children's children have the opportunities to experience the best of those things in life we have been able to take advantage of.

"From my point of view, having the time to interact with the natural world and to be part of a natural world that is sustainable is a critical element in that. If we destroy that, if we impair that in a way so it can't regenerate itself, in moral terms I think that is a sin," he says.

Huseby's parents were born in Norway, where they owned a fish market before moving to Alaska to work in a salmon cannery. Huseby grew up in Seattle and received a degree in history from Yale University. For 30 years he worked as a teacher and private-school administrator in Vermont before retiring.

Ettinger was born in the U.S., educated in New York and at Stanford University in California, and trained in photography. "A Sea Change" is the third documentary film she has produced.

Noting that Japan, like Norway, has long depended on the oceans for food and commerce, Sven is optimistic Japan will be a leader in solving the CO2 problem.

"My impression is that Japan is about as adaptive as any culture in the world, and if it is seen that sustainability and technology are going to create a marriage around clean tech, the Japanese are going to seize the day," he said.

"It is also my thought that if China and the U.S. can get their act together in terms of setting emissions targets, Japan will embrace and probably beat both countries to reaching those targets, because they are a more adaptable combination of government and industry. They are not going to be left behind," he added.

His real concern is closer to home. "I'm terribly worried about the U.S. getting left behind and not being a leader in this field," he said.

Water covers 70 percent of Earth's surface but, as Maya Lin notes in the film, 85 percent of our planet is unseen, due to undersea topography.

Here on the Maine coast, as I look out over the rocky shore and the sparkling North Atlantic, I wonder if humans can learn to care for such unseen magnificence, and its resources and mysteries that feed our bodies and souls.

One thing is certain, however: The vast majority of us alive today will live to see whether we learn, or fail. Either way, the future of the seas is in our hands, now.

For more information on the film, visit www.aseachange.net. A PDF version of Elizabeth Kolbert's "The Darkening Sea" can be found online. To read an interview with Kolbert, and her other writings, visit e360.yale.edu/ Stephen Hesse can be reached at [email protected]