Conservationists cheered in the spring of last year when thousands of green Kemp’s ridley sea turtles (Lepidochelys kempii) hit the beach, en masse and on schedule, to nest at Rancho Nuevo in Mexico’s northeastern state of Tamaulipas.

Rancho Nuevo serves as nesting ground for the vast majority of the world’s Kemp’s ridleys, the most endangered sea turtle. Since the late 1970s, Mexican conservation measures have helped bring the species back from just a few hundred nesting females to some 10,000 today.

But with the April 20 explosion and sinking of British Petroleum’s Deepwater Horizon oil rig in the Gulf of Mexico, a new question mark looms over the battered Kemp’s ridley. With millions of gallons of oil in the water, potentially threatening nesting beaches in both Texas and Mexico, the sea turtle could either limp through or face crippling population losses.

“This could be a catastrophic event for the Kemp’s ridley, which spends most of its life in the gulf and forages immediately in the area of the spill,” says Marydele Donnelly, director of international policy at the Caribbean Conservation Corporation, a non-governmental group in Gainesville, Florida. “The oil will contaminate or kill blue crabs the turtles feed on. It could harm the turtles’ skin, liver and productive fitness. And it could cause a disaster if it makes it onto the beaches at Rancho Nuevo and Padre Island, Texas, the two places where virtually the world’s entire population of Kemp’s ridley females nests from mid-April to July.”

Fears about the slick’s impacts on the Kemp’s ridley is just one of many environmental concerns burgeoning since the deepwater-well blowout, which by mid-May had sent rust-colored slicks into the gulf over an area of more than 6,000 square miles (15,540 square kms). Even as the crude seeped into the species-rich marshlands of the Mississippi Delta, scientists said it was still too early to know what the long-term impact of the spill would be, though many forecast fallout rivaling or exceeding that of the 1989 Exxon Valdez spill in Alaska.

Experts say species ranging from sharks to migratory birds could be threatened if BP is unable to get the spill under control. Critically endangered leatherback turtles (Dermochelys coriacea) that nest on the Caribbean beaches of Panama and Costa Rica and feed on jellyfish in the Gulf of Mexico might be in peril. So might the critically endangered hawksbill (Eretmochelys imbricata) which nests throughout the Caribbean and also feeds in the gulf.

Millions of songbirds cross the Gulf of Mexico in late April and May en route from their winter resting homes in Central and South America to their nesting grounds in North America. In their case, the threat was toxic smoke from the controlled burns set to eliminate surface oil.

The immense whale shark (Rhincodon typus), which migrates from the gulf as far as Brazil and is considered a vulnerable if not endangered species, feeds in the gulf from May to September. As a filter feeder, straining plankton and algae at the water’s surface, it risks having the fine, mesh-like filters that line its gill plates and pharynx clogged with oil.

“I have very deep concerns about these animals,” says Bob Hueter, director of the Center for Shark Research at the Mote Marine Laboratory in Sarasota, Florida. “You couldn’t design an animal that would be more vulnerable to an oil spill.”

Still, the most vulnerable species by far in terms of impacts on its overall population is the Kemp’s ridley.

After 1947, when 42,000 Kemp’s ridleys were filmed at their most important nesting beach near Rancho Nuevo, the turtles’ nesting population there dropped to only two hundred in the late 1970s and 1980s as a result of both egg collection and incidental capture during shrimp trawling, longline fishing and other commercial fishing enterprises.

Since then, though, the U.S. government’s National Marine Fisheries Service and a number of U.S. state agencies have imposed strict regulations on fishing gear and practices to reduce turtle bycatch.

Meanwhile, the Mexican government in 1990 banned the taking of sea turtles and in 2002 turned the beach at Ranch Nuevo into a Natural Protected Area, where the military protects the turtles during nesting season.

The possibility that oil could still be gushing out of the underwater well in August, when the prevailing currents shift direction and head south towards Mexico, has turtle conservationists worried. Mexico carried out a three-day drill in May on wildlife rescue and the containment and collection of oil. But if the oil reaches the beach at Rancho Nuevo, the world’s most important home for Kemp’s ridleys, it could be disastrous for nesting.

“If the nesting sites are affected or if the hatchlings born at these sites are affected, we could definitely see a devastating impact on this very localized, unique species of turtle that occurs almost exclusively in the gulf and is still critically endangered,” says Carlos Drews, director of the global species program for the environmental group WWF in Gland, Switzerland. “As we head into negotiations towards a global climate agreement in Cancun, Mexico this December, this is an eye opener about the risks that go along with continuing to base our economies on fossil fuels and the need to move as fast as possible into cleaner energies.”