"The turns are right there on the beach, and they nest on the shores of these barriers islands. Along with all of the other [potential dangers], they're going to have nests getting oil in them," Schoen said. (See shorebird pictures.)
Photograph by Dave Martin, AP
The Gulf oil spill comes at an especially bad time for Atlantic bluefin tuna, because the fish are now moving into their spawning grounds in the Gulf of Mexico.
According to the Tag-a-Giant Foundation, which tracks the movements of more than a thousand bluefin tuna, the area where the oil spill is centered is one of the fish's primary breeding grounds.
Tuna eggs and larvae can be severely harmed by just a few drops of crude oil, said Harry Blanchet, finfish program manager for the Louisiana Department of Wildlife and Fisheries. Larger tuna are at risk if they eat smaller fish that have themselves ingested the oil.
Floated to hold back oil from the Gulf spill, a containment boom creates an orange line in the water not far from nesting pelicans and other shorebirds on Louisiana's Breton Island on April 30. (See a map of Louisiana's barrier islands.)
The brown pelican—the state bird of Louisiana—is in critical danger due to the Gulf oil spill, because the species spends much of its time floating on the surface of the water. That means the crude can accumulate on the birds' feathers, causing them to lose buoyancy.
Oil also allows cool water to get past the birds' wet suit-like feathers and touch skin, compromising the pelicans' thermal regulation and making it harder for them to fly and dive for fish.
In addition, brown pelicans are currently in the middle of nesting season, and they tend to nest on beaches that appear in the path of the approaching oil slick. (See "Oil Spill Hits Gulf Coast Habitats.")
Photograph by Alex Brandon, AP
Dolphins surface in Breton Sound not far from the Louisiana coast on May 1, as gas wells loom farther out in the Gulf of Mexico.
Both young and adult dolphins are at risk of inhaling and ingesting floating oil, because the marine mammals must surface to breathe. With their soft skin, dolphins can also experience skin irritation from the oil, and eating tainted fish could poison the mammals.
Photograph by Gerald Herbert, AP
More than thirty dead sea turtles—including the one pictured near Pass Christian (map)—were found on the beaches of Mississippi in early May. Researchers have collected the bodies in an attempt to determine whether the turtles died due to the Gulf of Mexico oil spill.
Turtles are also known to “mouth and chew on anything” and will likely investigate large clumps of the toxic crude, Kelley said. Oil from well leaks is much thicker than the processed oil that spills during tanker accidents.
"This is what we'd call an 'unusual mortality event,'" Kelley added. "It's not good—you're dealing with animals that are still on the [U.S.] endangered species list."
Photograph by Dave Martin, AP
Reddish egrets, like the birds pictured above with their fledglings in a file photo, may have an advantage over pelicans in dealing with the Gulf oil spill. Since the egrets wade rather than float, they should get less oil on their feathers, said the Audubon Zoo's Schoen. (See pictures of wading birds.)
But reddish egrets along the U.S. Gulf Coast are still at risk of oil consumption, he said, because the birds feed in shallow waters where the crude is likely to accumulate.
Although the birds aren't listed as endangered, threats to their populations can pose serious risks, because the species has a long life span and a low reproductive rate. In general, reddish egret numbers have declined due to human encroachment and habitat loss.
Photograph by Robert Sisson, National Geographic
Sperm whales gather in their breeding grounds off the Caribbean island of Dominica in a file photo. The largest toothed whales on Earth, sperm whales are listed as vulnerable—or facing a high risk of extinction in the wild—by the International Union for Conservation of Nature.
A population of sperm whales lives near coastal waters just south of the Mississippi Delta, according to the Harte Research Institute for Gulf of Mexico Studies in Corpus Christi, Texas. Some of these whales may already be near the Gulf of Mexico oil spill, the National Oceanic and Atmospheric Administration reports.
The snowy plover, pictured preening in a file photo, is a small bird that spends much of its life running up and down shorelines in search of food. (See a picture of a snowy plover chick.)
The bird has been identified by the National Audubon Society as one of the species most vulnerable to the Gulf of Mexico oil spill. Snowy plovers risk not only direct contact with the oil but might also be poisoned by eating small invertebrates and oysters tainted with oil.
Photograph by Tim Laman
Plovers aren't the only oyster-eaters that might be at risk from oil-tainted food: Many of the oysters for human consumption in the United States come from beds along the Gulf Coast. Because of the Gulf oil spill, many of the oyster beds in Louisiana have already been shut down.
If the oil reaches deeper into Louisiana's wetlands, it could smother the oyster beds there, said Patrick Banks, oyster program manager for the Louisiana Department of Wildlife and Fisheries. Or, as the water warms, hatching oyster larvae could come in contact with oil, affecting a whole new generation of shellfish, he added.
Photograph by James L. Amos, National Geographic
Seen under a microscope, a splash of Hawaiian seawater teems with plankton—tiny plants, animals, and eggs that drift in the ocean.
As oil droplets from the Gulf of Mexico spill spread through the water column, the crude might prove fatal to plankton, which many larger animals depend on for food, marine biologist Earle recently told National Geographic News.
Rescue workers can clean and treat oiled birds and other relatively large animals that come ashore. But "how do you deal with de-oiling plankton?" Earle said.