(01-17) 04:00 PDT Cabo Pulmo, Mexico -- When Jesus Castro-Fiol died last year at the age of 107, he was survived by seven children, all living in this little settlement on the Sea of Cortez, and by two generations of grandchildren.

The four generations had many things in common: a rich sense of family, a dependence on the sea for their food and livelihood, and a respect for the natural wonders that draw tourists here over many miles of bumpy dirt roads -- the spectacular Cabo Pulmo Reef and the giant gray whales that migrate from the Bering Sea to give birth in the lagoons of Baja California Sur.

At one time, the Castros joined the throngs of people fishing the 7-mile-long reef. But in the last decades, they stopped taking sea life from the ocean nursery. Instead, they take scuba divers to it.

They became environmentalists, organizing Cabo Pulmo to protect the fragile reef, the northernmost living coral reef off North America, from the overfishing and injury that threatened it.

But in Castro-Fiol's last years, the family watched as a warming climate began to put their way of life at risk.

They saw parts of the reef sicken from a too-warm sea. They saw whales change their behavior, circling the Baja peninsula in new patterns in search of cool water. They saw a new tropical disease, dengue fever, emerge in Baja after a severe hurricane and kill a member of the family.

Ricardo Castro-Fiol, a grandson of Jesus Castro-Fiol who dives at the reef about once a day year-round, said the warming waters and stronger currents have changed the sea. "We can feel the difference,'' he said.

The death from dengue fever in 2003 of his aunt, Maria Castro, 54, who 30 years ago opened the only restaurant on the pristine beach, is the only known fatality from the disease in Cabo Pulmo.

Public health researchers warn that as global temperatures continue to rise, the mosquito species that carries the fever will multiply. In addition, models of how the Earth's warming will affect global climates indicate intensifying storms and flash floods that could aid the insect's spread.

Now when tropical storms come to Baja, many people fear more than losing electricity and roads washing out. The phrase common in Cabo Pulmo is "calentando'' -- global warming.

The coral

The reef starts only 100 yards off the beach, a lush underwater forest of red, orange, yellow and purple corals. Farther out, in 70 feet of water, divers find the coral's massive skeletons of calcium carbonate and nose into caves full of puffer fish, groupers, yellow-tailed angel fish, octopus, tiger sharks and turtles.

Coral reefs are the world's most biologically diverse ocean ecosystems. The reef, or frame, formed by living animals holds a million species in an intricate connection of lower organisms, fish, birds, turtles and marine mammals.

Fisheries near reefs supply protein to millions of the world's poorest people, an estimated one-quarter of the fish catch in developing countries. In such isolated communities as Cabo Pulmo, the portion is much higher.

But in the past 30 years, rising sea temperatures associated with global warming have been linked to a dramatic increase in the intensity and extent of damage to reefs known as bleaching.

Scientists warn that continued warming could weaken or wipe out corals around the world, and severely reduce the life in the ocean. They also warn that increased carbon dioxide in the ocean may impede the growth of the corals.

Jesus Castro-Fiol, a fisherman, was the first Castro to see the reef. Family lore says he could free-dive 75 feet for mother-of-pearl.

One by one, all the children found the vast underwater world -- three main reefs and seven smaller fingers. It was a prime fishing ground for the Castros and other commercial fishermen.

It wasn't until 1978 that Juan Castro-Montaño, a son of Jesus Castro-Fiol, began taking tourists out to the reef to dive. When the divers came back to the boat, they raved about the corals' beauty.

He wanted to see for himself, and went snorkeling. "When I saw the coral, I saw how fragile it was, how beautiful it was," Castro-Montaño said.

But, he added, "that was also when I realized how important it was, and we were destroying it.'' The divers, on the other hand, "weren't hurting anything. They were just taking pictures.''

Fishing boats took thousands of tons of sea life out of the corals every year. The reef was littered with fishing gear, anchors and harpoons left by Yankee whalers, which had broken corals that took decades to grow an inch.

He spoke to some political leaders and bureaucrats about preserving it, but could get no action. In the early 1980s, some teachers from the Universidad Autonoma de Baja California Sur turned up. They talked to him about his interest in the reef, and from then on they brought students.

By then, he didn't need to persuade his family and other people in town to change from commercial fishing to tourism, he said. "My cousins and my uncles were doing commercial fishing all day, and then they'd have to go to San Jose or La Paz to sell the fish. They'd see me taking tourists diving -- and I'd make more money.''

Cabo Pulmo finally got national attention after Jacques Cousteau came looking for Castro-Montaño in 1986, he said. In 1995 President Ernesto Zedillo signed a law creating the Cabo Pulmo National Marine Reserve, banning fishing. The village is still waiting for a management plan and for help from marine police in patrolling the reserve.

Oscar Arizpe-Covarrubias and Hector Reyes-Bonilla, coral researchers at the University of Baja California Sur, say the reef system, with 10 species of sea fans and other branched corals and 12 of stony corals, is one of the most stable in the eastern Pacific -- for now.

It suffered spots of bleaching in 1982-83 and 1997-98, periods of strong El Niños, fluxes of warmer water that come from the tropics.

"Now, we see mostly healthy coral and some bad coral,'' said Ricardo Castro-Fiol, the diver who takes tourists to the reef.

"I see some of the corals coming back,'' he said.

When water warms by 3 to 6 degrees, algae that live in symbiosis with the living coral disappear, exposing the white calcium carbonate skeletons of the coral colony. The bleaching can kill the corals.

The last bleaching event, in 1997-98, was the worst on record, and killed coral in parts of Asia, the eastern Pacific and the Caribbean.

As carbon dioxide levels in the atmosphere continue to rise, and the Earth's atmosphere and oceans both warm, these events will become common within 20 years, and will occur annually in most tropical oceans in 30 to 50 years, scientists predict.

If levels double by 2100, the heat tolerances of reef corals will be exceeded within a few decades, projects the United Nations Intergovernmental Panel on Climate Change -- a group of 2,000 scientists from 100 countries.

Oceanographers say damage to northern reefs such as Cabo Pulmo will lag behind changes in the tropics, where reefs already live at temperatures near their thermal limits. Scientists say corals can't evolve fast enough to shift to more hospitable regions as ocean temperatures change.

"Cabo Pulmo is of great ecological importance because it's the northernmost coral reef of the eastern Pacific,'' said Arizpe-Covarrubias, the researcher. "The animals and plants are different from elsewhere in the Pacific.

"And it's of great importance for the people living there. The quality of their lives is better now that they use the coral not for fishing but just for tourists.''

Whales

At this time of year, Pacific gray whales are returning to Baja California from their main feeding grounds in the Bering and Chukchi seas, a journey of more than 5,000 miles that is the longest migration of any mammal.

In their home lagoons on the Pacific Ocean side of the Baja Peninsula, females will bear and nurse the young before returning north in April.

At times, the whales swim around the peninsula to Cabo Pulmo on the East Cape. The whales bound in the waves, entertaining onlookers with their spouting antics.

The villagers think of the grays as the friendliest of the marine mammals. Mother gray whales come with babies to waters as shallow as 25 feet.

But just as warming ocean waters are affecting corals, the warming of Arctic and subarctic waters appears to be affecting whales. They are searching for food in different places in the north, just as they're changing swimming patterns in the Sea of Cortez.

At the University of Baja California Sur in La Paz, Jorge Urban-Ramirez, an expert on whales, coordinates the Marine Mammal Research Program.

He and his colleagues see the gray whale as an indicator of changing ecosystems, rather than an immediate victim. Unlike corals, sea stars and millions of other species, he said, whales can move, and they've done so over the millennia.

"The gray whales spend all of their life in shallow water on the continental shelf,'' he said. "If they want to live in a changing environment, they have to adapt to different encumbrances.''

During one La Niña year, when the water was colder than usual, the whales swam north in the gulf all the way to Kino Bay, looking for warmer water, he said. They had stopped swimming up there in the 1950s and 1960s when small boat traffic got too thick.

Why the whales migrate to the Arctic to feed might be tied to the end of past glacial periods, Urban-Ramirez said.

Perhaps whales were always born in the lagoons, he said, and they have always fed on fatty amphipods that live at the rich edge of sea ice. But 10,000 years ago, glaciers reached farther south in North America. When the glaciers receded, the amphipods went north and the gray whales followed.

Now, researchers say the whales' food supply is diminishing in the Bering Sea; amphipods have declined over the last 25 years as currents in the North Pacific Ocean warmed and sea ice gradually melted and thinned.

The warmest water temperatures on the continental shelf of the eastern Bering Sea were first recorded in the summer of 1997, the same El Niño year of the bleaching of corals in Cabo Pulmo and many parts of the world.

That year, a small phytoplankton replaced the normal summer phytoplankton, profoundly affecting the rest of the food chain, according to National Oceanic and Atmospheric Administration scientists. When the zooplankton couldn't eat the smaller phytoplankton, their numbers were reduced, seabirds starved, and salmon runs declined.

Since then, the warming trend has continued in the bottom level and at the top of the northern Bering Sea. The numbers of the whales' favorite amphipods and other sea life remain at low levels.

Hundreds of gray whales stranded dead along beaches from Mexico to Alaska on the northern migration in 1999 and 2000. Whale scientists counted 200 dead in Mexico and observed that one in 10 looked emaciated.

The cause of the deaths remains unknown. One theory is that the whales went to their traditional feeding grounds, found a poor food supply, and then had to forage in less rich seas.

"There are not as many whales being stranded as before,'' said Jackie Grebmeier, a biological oceanographer at the University of Tennessee who will go to the Arctic this spring to continue ecosystem studies.

"There are more gray whales traveling farther north to feed, and staying north longer.''

Dengue fever

In August 2003, Hurricane Ignacio raged over the tip of the Baja Peninsula with 105 mph winds and 15 inches of rain. The desert's rutted roads and the town's potholes filled with water. In previous years, people would suffer symptoms of dengue fever, a disease spread by mosquitoes. But that year, nearly everyone in the village was sick.

Maria Castro, the wife of Juan Castro-Montaño and mother of four, woke up ill on Sept. 1, six days after the hurricane. Over the next three days she went to two different clinics.

A health worker at the first clinic sent her home with some medicine. A doctor at the second clinic told her she shouldn't be taking the medicine. By then, ill and fevered, she was so dehydrated she needed intravenous fluids.

On the fourth day she died.

"We later found out that you're not supposed to take anything -- not anything, not vitamins, not anything, said her daughter, Angeles Castro-Murillo. "Only Tylenol and water.''

A border publication, Frontera Norte Sur, reported 1,319 suspected cases of the fever in Baja California Sur that summer.

International researchers began to warn that the cases raised concerns not only for the sick but also for future generations: if the Earth continues to warm, warmer temperatures and intensifying storms and floods would stimulate the reproduction of carrier mosquitoes of dengue fever, malaria and yellow fever.

According to the U.S. Centers for Disease Control and Prevention, about 5 percent of those who get dengue fever die, but with proper treatment, the rate can be reduced to 1 percent. There is no vaccine or medication.

In 2005, dengue was the world's most widespread mosquito-borne viral disease affecting humans, according to the CDC. As with malaria, an estimated 2.5 billion people live in areas at risk of epidemics. Already epidemics sicken millions a year with dengue fever, scientists say; only a small fraction of the cases get reported.

Last year, World Health Organization researchers reported that the worst outbreak in years was due to heavy rains and warmer temperatures. In Asia alone, dengue fever infected some 120,000 people in 2005, killing at least 1,000.

It takes freezing temperatures to kill eggs of Aedes, the mosquito carrier of both dengue and yellow fever. So, warming trends can shift the mosquito and the distribution of the disease to higher latitudes and altitudes, said Jonathan Patz, a University of Wisconsin environmental health physician who worked on the report.

Warmer water produces smaller adult mosquitoes, which have to feed more frequently to develop an egg batch, he explained. The time to develop the virus inside the mosquito also shortens with higher temperatures, increasing the proportion of mosquitoes that become infectious, he said.

In a Mexico study, the most important predictor of the prevalence of dengue was found to be the median temperature during the rainy season.

Beneath the shade of palm fronds at Maria Castro's open-air restaurant, La Palapa, Angeles Castro-Murillo was serving her mother's invention, "Enchiladas de Doña Maria,'' filled with chopped avocados and onions, banded with pale yellow cheese.

"My mother was a wonderful cook," she said. "She fed the divers. But she didn't like the ocean. We couldn't get her to go down to the water."

The death of her mother remains a heavy loss for the family, as does the fear that the carrier mosquito could return to Baja.

Life has changed in Cabo Pulmo, and the descendants of Jesus Castro-Fiol know it's just the beginning.

The warming ocean already has harmed the Cabo Pulmo coral reef in the Gulf of California. More than 5,000 miles north, the warming waters in the Bering Sea appear to be reducing the food supply of a Pacific Coast traveler, the gray whale.

Warming waters rob Arctic food supply

Every spring the Pacific gray whale returns from the lagoons along Baja's Pacific coast to the northern Bering Sea for its main annual feeding time. In the past 25 years, warmer water and air are melting sea ice and changing the Arctic ecosystem. In particularly warm years, the whales can't find their favorite fatty amphipods which they scoop out of the mud. They're staying longer in the north, searching for food in new feeding grounds, which raises concerns that the new prey may not be as nutritious.

Gray whale

Adult

45-50 feet long

15-35 tons weight

50-60 year lifespan

5,400+ miles: Gray whales have the longest yearly migration route of any mammal

Cabo Pulmo reef

Living coral reefs are the world's most biologically diverse ocean ecosystems. They support an intricate web of a million species, including fish, birds and marine mammals. The 7-mile long Cabo Pulmo reef is the northernmost in North America. Past El Niños caused damage to the corals, but they are slowly regrowing and remain healthy.

Coral symbiosis

Coral is made up of colonies containing thousands of small individual polyps. The living tissue of each polyp contains thousands of microscopic algae called zooxanthellae. These algae, through photosynthesis, produce food and provide the coral with 90 percent of its energy supply and increase growth.

Growth

Individual polyps secrete calcium carbonate at their base to extend the structure of the coral. Periodically a polyp can detach from the colony and then reattach, forming random openings in the coral mass.

Coral bleaching

Warming water temperatures stress the relationship between coral and algae, causing the algae's photosynthetic process to alter and produce toxins as a byproduct. The coral then loses the algae, resulting in a "bleaching" or whitening of its surface. The coral colony in that area dies.

Sources: National Center for Atmospheric Research; ESRI; National Oceanic and Atmospheric Administration, photo of coral and algae by NOAA

Chronicle environment writer Jane Kay and photographer Kat Wade traveled from Alaska to Mexico to see how global warming is changing life along the coast of North America.

Sunday: Polar bears signal change in Arctic.

Monday: Subtle seaside transformation in California.

Today: A family's way of life threatened in Mexico.