Expensive jet fuel and a soft American economy are threatening to sink Caribbean tourism as airline ticket prices soar and flights are sharply reduced, choking the flow of the vacationers that many tiny islands depend upon.

Tourism is the economic cornerstone of the Caribbean, which drew more than 15 million visitors last year to colonial cities and carefree beaches.

"Billions of dollars of investment are being exposed and thousands of jobs are being exposed," said Allen Chastanet, chairman of the Caribbean Tourism Organization.

Airlines are cutting back across the world as passengers balk at paying fares that have risen along with fuel costs. The Caribbean is particularly vulnerable because one foundering airline, American, controls much of the market -- carrying more than 60 percent of passengers traveling through Puerto Rico last year.

American now expects to cut daily flights out of Puerto Rico's capital from 93 to 51 in September. Some flights will be cut to Santo Domingo, Antigua, St. Maarten, Aruba and Samana in the Dominican Republic, spokeswoman Minnette Velez said.

Fewer flights to Puerto Rico also could jeopardize the island's cruise ship industry, since it would be harder for passengers to reach the island to board.

Rather than raise ticket prices so high that they're beyond the reach of most customers, American has decided to cut flights and reduce capacity, Velez said. "Traveling would be completely inaccessible if

Other carriers are making similar moves. Spirit Airlines recently said it would close its San Juan hub, and Continental Airlines expects to soon announce destination and flight cuts.

The Caribbean is still affordable for wealthy travelers, but resorts "that appeal particularly to price-sensitive families are in a world of trouble," said Christopher Hart, professor at the Cornell University School of Hotel Administration.

The flight cuts are coming despite increases in tourism this year to most of the islands, including double-digit growth in U.S. visitors to Antigua, St. Lucia and Jamaica, according to the Caribbean Tourism Organization.

The Dominican Republic reported 407,000 U.S. tourists from January to April, a 6 percent increase from last year, and Puerto Rico reported increased airline passenger traffic as well.

Now many fear even more cuts, meaning the islands won't have a chance to lure more tourists.

"This is just the beginning," said Peter Muller, a German native who owns the Hotel Coyamar in Samana, the Dominican Republic. "We're going to reach a point where it's no longer worth keeping the airport open."

In Antigua, where tourism officials tried to lure visitors over the weekend of June 14-15 with a music festival featuring Lionel Richie and Kenny Rogers, most of the tickets sold were to locals, festival chairman Alvin Edwards said.

The U.S. Caribbean territory of Puerto Rico, the region's main tourism gateway, has offered to reduce low-season airport fees by as much as 45 percent to persuade airlines to reconsider.

Flying against the trend is JetBlue, which plans to add daily flights to Puerto Rico from New York; Orlando, Fla., and Boston starting this fall, and Virgin Atlantic president Richard Branson said he also might add extra flights from the U.S. to the Caribbean.

"Virgin America is a great airline, it's doing very well," Branson said. "We have young planes, which are more fuel-efficient than the ones American Airlines has."

Smaller islands are asking regional carriers such as LIAT and Air Jamaica to increase flights and coordinate schedules to fill gaps left by American, said Chastanet, who is also St. Lucia's tourism minister.

Some islands also are turning to Europe, where the euro has risen against the dollar, making Caribbean vacations more attractive.

"There's an opportunity, given the strength of the euro," said Allegra Kean-Moorehead, spokeswoman for the U.S. Virgin Islands Tourism Department. "It's a market that has a huge amount of potential."