Workers clean up tar along Pensacola Beach [Photo:Michael Spooneybarger/AP]

• Most at Risk

» Northwest Florida. The tourism industry in just the five coastal counties closest to the spill generates some 55,000 jobs. Commercial fishing and aquaculture are at risk as well: Ninety percent of oysters in Florida come from the Apalachicola estuary system. Oil contaminant could suffocate the oysters, and persistent hydrocarbons could make oysters inedible for some time. Gulf Islands National Seashore, which stretches 160 miles from northwest Florida to Mississippi, is the largest seashore among national parks and is home to 14 threatened or endangered species.

Key West shrimp boats at dock

» The Keys. The islands’ tourism economy, valued at $2.2 billion in 2008, represents 60% of the economy and 57% of employment. Commercial fishing ranks alongside tourism as a primary Keys industry, producing some 20 million pounds of seafood and marine products per year. Commercial fishermen operate more than 300 boats, and it’s estimated the catch includes more than 80% of the spiny lobsters harvested in Florida. One of the planet’s largest coral reef systems stretches from the Dry Tortugas National Park in Monroe County to Biscayne Bay east of Miami.

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• Impact So Far

» Even before oil sheen and tarballs began washing ashore in northwest Florida, fear of the spill’s effects had already cut into this year’s summer tourism season. Cancellations began coming in by early June, and phone calls for reservations lessened. By early June, the spill had closed more than a third of fishing areas, impacting both commercial and sport fishing interests, including deepwater fishing tournaments. In the Keys, meanwhile, tourism executives reported cancellation of 25% to 40% of bookings in the first month after the spill. Half of all summer visitors come for fishing, diving or boating. Because of the spill, the state opened the oyster harvest season early. Business activity associated with monitoring and cleanup— travel and accommodations, for example — was notable in some places but vastly outweighed by the impact of the spill on usual commerce.

• oil spill dynamics

Workers set up booms to try to contain the oil along Pensacola's Beach [Photo: Joe Raedle/Getty]

» Pollution and Dilution. While the volume of the spill is tiny compared to the overall volume of water in the Gulf, the oil will remain concentrated in upper water levels, intensifying the pollution. A bright spot: Oil breaks down faster in warmer climes: During the first few days after a spill, 20% to 40% of oil’s mass turns into gases and loses most of its water-soluble hydrocarbons. Between 10% and 30% of the oil is absorbed by sediments and suspended materials and deposited on the bottom of the sea. Once there, however, oil stops decomposing because there’s little to no oxygen.

» Natural Processes. Miles of booms haven’t prevented oil sheen from reaching beaches in northwest Florida. Most of what washes up in Florida, however, is likely to be “tarballs” and “tar patties” — pliable lumps of weathered oil that form as a slick scatters into small patches. They can be as small as a wedding ring to as large as a plate and can wash ashore hundreds of miles from — and many months after —an oil spill. Tarballs have to be picked up by hand or with beach-cleaning machinery.

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• Wild Cards

» Loop Current: The current flows northward in deep water between Cuba and the Yucatan Peninsula, then twists west and south through the Gulf down through the Florida Straits. Winds and changes in the current will have a lot to do with how much oil comes ashore in Florida.

» Hurricanes: A hurricane in the Gulf could disrupt cleanup efforts — or the drilling of a relief well — and spread the oil and tarballs over a greater region.

» BP: The earliest the company can complete a relief well — the only complete solution to the spill — is August. It could take more than one try, making the timeline less certain.

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• Longer Term

» Ongoing monitoring everywhere. Tourism and fishing interests will likely be monitoring Gulf waters for oil pollution for years after the spill is finally plugged. Compact, mobile sensors called fluorometers can detect oil quantities as low as one part per million in seawater and can be used from aboard boats as well as from shore. Scientists can also use the fluorometers to assess the interaction between oil contamination and phytoplankton blooms, including red tide. Scientists are expecting a wave of red tide this year, and little is known about how oil in the Gulf will affect red tide.

» Is Drilling off the Florida Coast Dead? U.S. Sen. Bill Nelson and Florida Gov. Charlie Crist have both declared expanding offshore drilling dead in light of the BP spill. Other former supporters, including incoming House Speaker Dean Cannon, who was expected to push the issue during the next legislative session, have withdrawn their support. The nation’s dependence on oil remains, however, and barring some major change in the nation’s energy supply, pressure to drill is likely to return at some point.

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• Precedents and Context

» The Ixtoc I well blowout and explosion in June 1979 in the Bay of Campeche in Mexico dumped more than 3 million gallons of oil into the Gulf. It took Pemex, the Mexican government oil company, nine months to cut off the oil flow. The spill hit south Texas two months after the well exploded. The slick that hit the beaches was between 30 and 50 feet wide and between an inch and more than a foot deep. Despite its size, the Ixtoc spill has left relatively little lingering damage in the Gulf.

Texas shorline after Ixtoc I well blowout in 1979

» The Montara well blowout and fire in August 2009 in the Timor Sea, between Australia and Indonesia, dumped up to 85,000 gallons of oil per day into the ocean for more than 10 weeks. At one point, an oil sheen covered nearly 10,000 square miles of the sea’s surface. Damage to coastal areas was minimal because of the rig’s location far from land, but the spill occurred in a migration corridor for whales, turtles and other sea life.

• Three Years From Now?

» Months after the Ixtoc I oil spill about 600 miles south of Texas was finally capped, Luis Soto, a deep-sea biologist, told Tim Johnson, Mexico City bureau chief for McClatchy Newspapers: “I found shrimp with tumor formations in the tissue, and crabs without the pincers.” Two years after the spill, scientists said the marine environment had begun to recover, however. “We were really surprised,” Mexican marine biologist Leonardo Lizarraga Partida told Johnson. “After two years, the conditions were really almost normal.” By year three, aquatic life along the Texas shoreline had returned to normal — even as tarballs continued to wash ashore. BP’s Deepwater Horizon is about 150 miles from Florida’s northwest coast and 400 miles from the western edge of the state. The spill is expected to hit 50 million gallons this month.