DRY TORTUGAS — Thirty feet down in the uncharacteristically chalky water of Bird Key Reef, the effects of recent hurricane activity is obvious.

Whole coral heads and coral fragments of various sizes and species lie shattered on the sea floor after tumbling in underwater avalanches from tall ridges; sea fans, sea whips, sea rods and sponges sprawl uprooted and scattered like trees in a storm-battered forest.

Earlier this month, state and federal scientists got their first look at damage done by hurricanes Charley and Ivan to coral in Dry Tortugas National Park. The reef was hit hard, but not all the news was bad.

The eye of Charley passed within 45 miles of the Dry Tortugas on Aug. 13 when it was a Category 2 storm with sustained winds of 110 mph; on Sept. 14, the eye of Ivan passed the Dry Tortugas about 200

Scientists assess coral damage from season's hurricanes in the Keys miles out as a Category 4 storm with winds of 140 mph.

"There were 50-foot waves in the eastern Gulf during Ivan: That's a hell of a lot of energy rolling in on a shallow system," said Walt Jaap, a coral expert at the Florida Fish and Wildlife Research Institute. "A hurricane with 50-foot waves will have an effect 100 feet deep.

"The reef suffered a good bit from Charley and Ivan, but it looks like it will probably survive, unless something else comes along."

The Keys reef tract, including Dry Tortugas reefs, fuel the Keys economy.

According to a recent federal study, more than 820,000 trips were made to the reef tract for recreation from June 2000 to May 2001. Non-Keys residents, including thousands of divers, snorkelers and fishermen from Southwest Florida, spent $614 million and Keys residents spent $77.4 million on reef-related activities.

Despite its remoteness, the Tortugas reef attracts plenty of attention.

"It's one of the most incredible places in the world," said Steve Olive, 52, of Fort Myers, who has visited the Tortugas regularly since 1977. "It's got really neat coral formations and great diversity and one of the most incredible fish populations in the world.

"I've had the opportunity to dive all around the Caribbean, and with the exception of one or two places, you can't touch the Dry Tortugas."

Simply put, the Keys reef tract and the Tortugas are a big draw, and any damage done to it is a big deal.

With coral reefs in the Keys already in decline because of disease and bleaching, Charley and Ivan just "added insult to injury," said Debbie Santavy, a research ecologist for the United States Environmental Protection Agency.

When a hurricane hits land, one neighborhood might be destroyed while the neighborhood next to it sustains little or no damage.

Same with coral reefs.

"Some get trashed more than others," Santavy said. "It depends on how exposed the area is, its location and how the wave energy hits it. Is it shallow, taking heavy seas? Or is it in the lee so it's not taking heavy seas?"

In some cases, corals were knocked down because they were already weakened by bio-eroding sponges, such as the red boring sponge (Cliona delitrix).

"The bio-eroding sponges eat away at the base," Jaap said. "And when you get a storm event, they break off and fall."

Storm-related coral deaths weren't always the result of being blown down.

"In some cases, the coral's tissue was in relatively poor condition, and the hurricanes came and finished them off," Santavy said. "Many of the skeletons looked sandblasted, especially elkhorn coral — there was no tissue.

"Usually a coral skeleton has defined features, but they were often all eroded away."

Hurricane activity might indirectly have caused coral bleaching, Jaap said.

Bleaching, a major problem worldwide, is a breakdown in the symbiotic relationship between coral polyps and algae called zooxanthellae (pronounced zoh-zan-THEL-ee).

The algae live in coral tissue, where they carry on photosynthesis and supply coral polyps with energy and oxygen — the zooxanthellae also transfer their colors to the colorless polyps.

When polyps become stressed, they expel the algae, lose color and appear bleached out.

If the stress disappears, the algae return; if not, they don't, and the polyps die.

Many things can cause stress to coral polyps, including lack of light.

"The corals might have been stressed from lack of light because the water was so milky after the storms," Jaap said.

Hurricane news at the Dry Tortugas reefs was not all bad.

Some broken corals might re-establish themselves, depending on how they landed, said Lauri MacLaughlin, a Florida Keys National Marine Sanctuary resource manager.

"If they landed upright, they might make it," she said. "Some colonies roll in a storm, die on one side and grow on the other."

Hurricanes actually can benefit a reef system.

The thin branches of elkhorn and staghorn corals, which recently were nominated as candidates for the Endangered Species List, break easily and scatter in storms, Jaap said.

"If they find themselves in a good place, they can fuse themselves to the bottom," he said. "If a colony breaks off 15 pieces, and 10 survive, you could have 10 new colonies.

"Larger pieces tend to be more successful, but success is probably more a function of where it lands than the size of the animal."

Jaap already has noticed staghorn fragments growing in seagrass beds in the Dry Tortugas.

Other positive aspects of the storms:

"There used to be a lot of benthic algae out here, but the storms came along like a vacuum and cleaned them," Jaap said. "That's a good thing: When coral spawns, the larvae need good habitat to settle on.