SOUTH KINGSTOWN — Outspoken marine ecologist Jeremy Jackson says humans have caused widespread and difficult-to-imagine damage to the world’s oceans and that the response needs to be of immense proportions. He says it boils down to two simple concepts: Become citizens instead of consumers, and elect real leaders, not facilitators of consumption.

“I felt good last Tuesday,” Jackson said of the election of Barack Obama, who on Tuesday was televised pledging a federal cap-and-trade system to limit carbon dioxide emissions and to invest billions in alternative energy. The hundreds of people attending the Fall 2008 Honors Colloquium on Global Environmental Change at the University of Rhode Island responded with enthusiastic applause.

Jackson, a 66-year-old ecologist at the Scripps Institution of Oceanography in California, said he realized about 15 years ago that many of the sea grass beds and coral reefs he studied as a young man were largely gone. That includes the grass beds of Chesapeake Bay and Florida Bay, and the reefs of Jamaica. Much of Australia’s Great Barrier Reef looks like a garbage dump, Jackson said. Fish populations are dramatically reduced and dead zones are growing in oceans around the world.

“It’s become obvious that [humans] are the cause,” Jackson said. “How could we be so out of it? The oceans were out of sight and out of mind and nobody was paying attention. As a marine ecologist, it’s embarrassing.”

He introduced the audience to the “shifting baseline syndrome,” in which people tend to think of the natural world as it was when they were teenagers. One result, he said, is that as people get older, they see the natural world deteriorating and they become “depressed.”

But more important, he said, people forget that considerable deterioration occurred before they became teenagers. What baseline is appropriate?

Jackson said his two environmental heroes were Rachel Carson, author of Silent Spring, and C. David Keeling, the scientist whose observations of increases in atmospheric CO2 sounded the alarm about climate change.

Jackson said humans have had six major impacts on the oceans:

• Overfishing: As recently as 1900, there were lots of fish in the oceans; now most fish populations are depleted.

• Destruction of the sea floor: Trawling for fish is akin to dragging a locomotive across the land, Jackson said. It flattens the bottom and destroys its ecology, much like clear-cutting destroys forests.

• Introduced species: Jackson described an introduced plant that is covering much of the bottom of the northwest Mediterranean. It destroys diversity on the sea floor, and no one knows how to stop its spread.

• Warming and acidification: Climate change is warming the oceans and carbon dioxide is making them more acidic, killing coral reefs and threatening to interfere with the chemical processes that create seashells. In one season recently, 80 percent of the coral reefs in the Indian Ocean bleached and a quarter of those died.

• Poisoned food webs: Jackson said spawning salmon bring with them loads of mercury that contaminates the streams where they breed and the animals that eat their carcasses.

• Eutrophication: Jackson calls it the “rise of slime.” Chesapeake Bay once had so many oysters they filtered all the water in the bay in a few days. But excessive nutrients from farms and golf courses fueled algae blooms that triggered low oxygen conditions when the algae died. Jackson said the “dead zones” are now populated by little more than jellyfish and bacteria.

“Can we put Humpty Dumpty back together again?” Jackson asked. “We have no idea.”

But he said there is cause for hope. He said studies of the Line Islands in the Pacific show that an uninhabited island is surrounded by lots of fish and coral, while similar but populated islands had dramatic declines in fish and coral. Those examples, Jackson said, suggest that marine sanctuaries can help bring back marine life.

It is essential, Jackson said, for people to reduce nutrient runoff and carbon emission and stop overfishing during the next few decades.

“The notion that we’ll have sustainable wild fisheries like we had in the past and feed nine billion people is just stupid.”

For a Web site based on the “shifting baselines” theme, go to www.shiftingbaselines.org/index.php

For an essay on shifting baselines by Randy Olsen, go to: www.articles.latimes.com/2002/nov/17/opinion/op-olson17.

plord@projo.com