When oil comes ashore at Gulf Islands National Seashore from the blowout of the Deepwater Horizon well, what impacts might wildlife that use the seashore encounter?

A lot depends on what form the oil shows up as, and how much there is. According to the U.S. Fish and Wildlife Service, "the season and weather, the type of shoreline, and the type of waves and tidal energy in the area of the spill" all affect how the oil can affect wildlife and fisheries.

According to the Fish and Wildlife Service's Alaska office, which dealt with the spill from the Exxon Valdez back in 1989, "Oil can be categorized into five groups, ranging from very light to very heavy oils. Most oil has a density less than water, so it floats. Oil tends to spread into a thin layer on the water surface as a sheen. Once in the water, oil undergoes weathering, a process that describes the physical, chemical, and biological changes that occur when oil interacts with the environment."

"Weathering reduces the more toxic elements in oil products over time, as exposure to air, sunlight, wave and tidal action, and certain mircoscopic organisms degrades and/or disperses oil," the agency notes.

Here's a list of some of the wildlife that frequent Gulf Islands National Seashore:

* Perdido Key Beach Mouse

* Brown Pelican

* Gopher Tortoise

* American Alligator

* Piping Plover

* Least Tern

* Loggerhead Sea Turtle

* Green Sea Turtle

* Leatherback Sea Turtle

* Kemps Ridley Sea Turtle

* Gulf Sturgeon

* West Indian Manatee

* Little Blue Heron

* Reddish Egret

* Snowy Egret

* Tricolored Heron

* White Ibis

* Black-crowned Night Heron

* Osprey

* American Bald Eagle

* Peregrine Falcon

* Merlin

* Sharp-shinned Hawk

* Swallow-tailed Kite

* Gray Kingbird

* Gulf Salt Marsh Snake

* Gopher Tortoise

* Mississippi Diamondback Terrapin

* Alligator Snapping Turtle

* Saltmarsh Topminnow

* River otter

* Atlantic Bottle-nose Dolphins

* Southern toad

Some key points from the USFWS concerning wildlife, fisheries, and oil spills:

* Wildlife are harmed by oil by physical contact with oil, ingestion, inhalation, and absorption;

* "Floating oil can contaminate plankton, which includes algae, fish eggs, and the larvae of various invertebrates. Fish that feed on these organisms can subsequently become contaminated. Larger animals in the food chain, including bigger fish, birds, terrestrial mammals, and even humans may then consume contaminated organisms."

* "Initially, oil has the greatest impacts on species that utilize the water surface, such as waterfowl..."

* "Physical contact with oil destroys the insulation value of fur and feathers, causing birds and fur-bearing mammals to die of hypothermia. ... In efforts to clean themselves, birds ... ingest and inhale oil. Ingestion can kill animals immediately, but more often results in lung, liver, and kidney damage and subsequent death."

* "Fish can be impacted directly through uptake by the gills, ingestion of oil or oiled prey, effects on eggs and larval survival, or changes in the ecosystem that support the fish."

On Friday, the president of the American Bird Conservancy said the Gulf oil spill "spells disaster for birds in this region and beyond.”

“It is ironic that next weekend is International Migratory Bird Day," added George Fenwick. "At a time when we should be celebrating the beauty and wonder of migratory birds, we could be mourning the worst environmental disaster in recent U.S. history.”

The Gulf Coast is extremely important for hundreds of species of migrants, which variously breed, winter, and rest here during migration, the organization said. The population effects on birds from this spill will be felt as far north as Canada and Alaska, and as far south as South America, it added.

ABC officials note that "all coastal nesting species (herons, terns, skimmers, plovers, gulls, rails, ducks) are currently present on the Gulf Coast, including several species on the U.S. WatchList of birds of conservation concern. The impact to these species depends on how long the leak lasts and what happens with weather and currents. The leak could persist for weeks or months, and end up being the worst environmental disaster in U.S. history."

Gulf Islands National Seashore provides key habitat for "thousands of wintering shorebirds, including endangered Piping Plover, Wilson’s Plover, and American Oystercatcher, as well as Brown Pelican, Black-crowned Night-Heron, White Ibis, and Black Skimmer," according to the organization.

Among other species that could suffer from the spill is a diminutive turtle that makes coastal Alabama home. And according to University of Alabama at Birmingham biologists who have studied the Diamondback Terrapin turtle, the spill could set back years of conservation work.

“Any community of organisms in the path of that spreading oil slick is in danger, and that is especially the case for a species like the Diamondback Terrapin turtle that is teetering on the brink of extinction in Alabama,” says Thane Wibbels, Ph.D., the UAB biologist leading efforts to save the terrapin.

Another species that could be affected is the West Indian Manatee. U.S. Environmental Protection Agency biologists say "the effects of discharged oil on adult manatees’ body temperature as a result of direct contact with oil is negligible because they have a layer of blubber for insulation. Also, they exhibit no grooming behavior that would contribute to ingestion. However, manatees may be affected by inhaling volatile hydrocarbons while they are breathing on the surface, and it is very likely that exposure to petroleum would irritate sensitive mucous membranes and eyes."

According to the EPA, a number of methods can be used to try to keep wildlife out of oil. Sometimes hazing can be employed to keep birds and animals away from oiled areas. "Visual deterrents include shiny reflectors, flags, balloons, kites, smoke, scarecrows, and model predators," the EPA says. "Auditory methods often rely on loud noises generated from propane cannons, alarms, model wildlife distress calls, predator recordings, and other noise makers."