On Florida's Panhandle beaches, where local officials once fretted over how much oil washed in with each new tide, everything seems normal. The tourists have returned. The children have gone back to splashing in the surf and hunting for shells.

Every now and then, a tar ball as big as a fist washes ashore. That's the only apparent sign that the worst environmental disaster in U.S. history tainted these sugar-white sands two years ago.

But with an ultraviolet light, geologist James "Rip" Kirby has found evidence that the oil is still present, and possibly still a threat to beachgoers.

Tiny globs of it, mingled with the chemical dispersant that was supposed to break it up, have settled into the shallows, mingling with the shells, he said. When Kirby shines his light across the legs of a grad student who'd been in the water and showered, it shows orange blotches where the globs still stick to his skin.

"If I had grandkids playing in the surf, I wouldn't want them to come in contact with that," said Kirby, whose research is being overseen by the University of South Florida. "The dispersant accelerates the absorption by the skin."

As those blotches show, the gulf and its residents are still coping with the aftermath of the Deepwater Horizon disaster, which began with a fiery explosion aboard an offshore drilling rig on April 20, 2010.

Even before BP managed to shut off the undersea flow on July 16, 2010, observers ranging from Time magazine to Rush Limbaugh insisted that the ecological damage from the 4.9 million barrels of oil that spilled seemed far less severe than everyone had predicted.

Now, after his company has spent $14 billion on cleanup and restoration in two years, BP spokesman Craig Savage said this month, "the beaches are open, the tourists are back and commercial fishing is rebounding."

But biologists are finding signs of lingering — and perhaps growing — damage throughout the gulf, from the bottom of the food chain to the top:

• Scientists have confirmed that tiny creatures called zooplankton accumulated toxic compounds from coming in contact with the Deepwater Horizon oil. Because small fish and crustaceans eat the zooplankton and are then eaten by larger fish, that means those compounds could now be working their way up the food chain, they said.

• Three months after BP shut off the flow of oil, scientists searching the floor of the gulf found a colony of deep sea corals that were covered in what they described as "frothy gunk." They were in the area where undersea plumes of oil had been spotted. Nearly half were dead. Extensive tests resulted in a finding, released just last month, that the culprit was in fact oil from Deepwater Horizon.

• This month, crews from the U.S. Fish and Wildlife Service fanned out to rivers across the coast to catch and take samples from sturgeon swimming upstream from the gulf to spawn. The reason: When scientists examined the sturgeon that swam upriver last year, they found "significant levels" of DNA fragmentation in the 300-pound fish that could have been caused by exposure to the oil spill, said wildlife service chief investigator Glenn Constant.

"It can lead to a number of abnormalities, such as cancer, tumors, challenges to their immune systems," Constant said. Reproduction could falter, too, he said.

• A survey last summer by USF scientists found that the highest frequency of fish diseases occurred in the area where the oil spill was. While scientists were initially cautious about attributing the lesions on red snapper and other fish to Deepwater Horizon, subsequent laboratory tests have all but eliminated everything other than the oil from the spill as the cause.

"It would be hard to argue otherwise," USF scientist David Hollander said this month.

• Biologists have become alarmed about how many bottlenose dolphins are washing ashore sick or dead across the gulf, from Texas to Florida — more than 600 during a time when the normal average is 74 a year. In Louisiana's Barataria Bay, where waves of thick oil washed in throughout the spill, dozens of dolphins have been found suffering symptoms of liver and lung disease and possible immune system failures.

Savage, of BP, points out that the jury is still out on most of those findings, and that much of the research being done on the impact of the spill is being funded by $500 million that his company donated to make up for the damage. Kirby's study is an exception — his funding comes from the Surfrider Foundation, a group founded by surfers to work on ocean protection issues.

Some good news has emerged since the spill. For instance, sperm whales apparently avoided contact with the oil, swimming clear of that section of the gulf. Biologists say bluefin tuna, which were spawning during the spill, appear to have suffered only minimal effects. And a "dirty blizzard" that USF scientists discovered littering the gulf's bottom with dead organic matter after the spill has now mostly dissipated, Hollander said.

Still, serious questions remain. A massive study of everyone who came in contact with the oil began last year, overseen by the National Institutes of Health. So far, thanks in part to an offer of a $50 gift card for participants, the study has signed up 8,000 people, half of them from Florida, said Dr. Dale Sandler, who's in charge. She hopes to have 40,000 by the end of the year and to follow the fluctuations of their health for a decade.

"People are concerned," Sandler said. "There are pockets of people there who have poor health and came into contact with the oil. Putting two and two together, they think the oil spill is responsible for their illness. Our job is to sort that out."

Kirby, the USF geologist, is concerned too, based on what his ultraviolet light has shown him.

The oil he found lies in what's called the swash zone, just below where the waves lap against the sand. When a "plunge step" forms there, small flakes of weathered oil or even large tar patties settle there, mingled with shell debris, he found.

Studies have found that the dispersant used to break up the oil slick, Corexit, can be toxic to the bacteria that would normally gobble up oil in the gulf. That's why the oil is still showing up two years later, he said. When Corexit bound with the oil, it prevented bacteria from consuming it.

The concentrations of toxic hydrocarbons in the flakes and patties are above the level considered to be dangerous under federal standards, he said. That's what makes him so concerned about how quickly the dispersant-mixed oil absorbs into human skin.

Kirby consulted with three toxicologists about it. Two recommended an immediate study of what level of toxic oil might be absorbed. The third, a state employee, was less concerned, he said.

According to Savage, only 8 miles of gulf beaches are still undergoing cleanup paid for by BP. Kirby thinks someone should be surveying every beach's swash zone every morning to check for the little oil-and-dispersant globs he found.

Given how toxic those globs might be, he said, "would you let your kid play in the shallow water and absorb toxic tar product? Wouldn't you rather have a sign that told you the beach was hazardous in certain spots?"

Information from the New Orleans Times-Picayune was used in this report. Craig Pittman can be reached at craig@tampabay.com.