Here on the open ocean, 12 miles from ground zero of the Deepwater Horizon oil spill, the gulf is hovering between life and death.

The large strands of sargassum seaweed atop the ocean are normally noisy with birds and thick with crustaceans, small fish and sea turtles. But now this is a silent panorama, heavy with the smell of oil.

There are no birds. The seaweed is soaked in rust-colored crude and chemical dispersant. It is devoid of life except for the occasional juvenile sea turtle, speckled with oil and clinging to the only habitat it knows. Thick ribbons of oil spread out through the sea like the strips in egg flower soup, gorgeous and deadly.

A few dead fish float in the water, though dolphin-fish, tuna, flying fish and the occasional shark can still be seen swimming near the surface, threading their way through the wavy, sometimes iridescent gobs of crude.

“This is devastating. I mean literally, it’s terrible. All this should be pretty much blue water, and — look at it. It just looks bad,” said Kevin Aderhold, a longtime charter fishing captain who has been taking a team of researchers deep into the gulf every day to rescue oil-soaked sea turtles.

“When this first happened, a lot of us were like, they’ll cap that thing and we’ll be out fishing again. Now reality’s set in. Look around you. This is long-term. This’ll be here for-ev-er.”

And then it gets worse. When the weather is calm and the sea is placid, ships trailing fireproof booms corral the black oil, the coated seaweed and whatever may be caught in it, and torch it into hundred-foot flames, sending plumes of smoke skyward in ebony mushrooms. This patch of unmarked ocean gets designated over the radio as “the burn box.”

Wildlife researchers operating here, in the regions closest to the spill, are witnesses to a disquieting choice: Protecting shorebirds, delicate marshes and prime tourist beaches along the coast by stopping the oil before it moves ashore has meant the largely unseen sacrifice of some wildlife out at sea, poisoned with chemical dispersants and sometimes boiled by the burning of spilled oil on the water’s surface.

“It reflects the conventional wisdom of oil spills: If they just keep the oil out at sea, the harm will be minimal. And I disagree with that completely,” said Blair Witherington, a research scientist with the Florida Fish and Wildlife Conservation Commission who has been part of the sea turtle rescue mission.

By unhappy coincidence, the same convergences of ocean currents that create long mats of sargassum — nurturing countless crabs, slugs and surface fish that are crucial food for turtles, birds and larger fish — also coalesce the oil, creating islands of death sometimes 30 miles long.

“Most of the Gulf of Mexico is a desert. Nothing out there to live on. It’s all concentrated in these oases,” Witherington said.

“Ordinarily, the sargassum is a nice, golden color. You shake it, and all kinds of life comes out: shrimp, crabs, worms, sea slugs. The place is really just bursting with life. It’s the base of the food chain. And these areas we’re seeing here by comparison are quite dead,” he said.

“It’s amazing. We’ll see flying fish, and they’ll land in this stuff and just get stuck.”

Hardest hit of all, it appears, are the sea jellies and snails that drift along the gulf’s surface, some of the most important food sources for sea turtles.

“These animals drift into the oil lines and it’s like flies on fly paper,” Witherington said. “As far as I can tell, that whole fauna is just completely wiped out.”

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The turtle rescue team sets out at 6 a.m. in the muggy warm stillness of the harbor at Venice, La. The researchers move into the open gulf about an hour later, past a line of shrimp boats deputized to lay boom along the coastal marshes.

Closer to the Deepwater Horizon site, the water takes on a foreboding gray pallor tinged with a rainbow-like sheen. Soon, the oil begins swirling around the boat and the seascape smells like an auto mechanic’s garage.

Strewn among the oil and seaweed are human flotsam: an orange hardhat, a pie pan, a wire coat hanger, yellow margarine-tub lids, a black-and-green ashtray. The crew has found papers — long at sea on global currents — bearing inscriptions in Spanish, Arabic, Greek and Chinese.

The only sound that breaks the stillness is the deep thrum of the motors of the large charter boat and a small skiff carrying the turtle researchers. From dawn until nearly dusk, across sargassum islands that normally are alive with birds looking for crabs and snails — bridal terns, shearwaters, storm-petrels — only one bird is seen.

“What’s amazing is there’s so little bird life out here right now. Either they’ve moved on, or the oiling has had a tremendous impact,” said Kate Sampson, a researcher with the National Oceanic and Atmospheric Administration who is part of the turtle rescue team.

“We saw a few yesterday. We saw a few laughing gulls fly by. They were oiled, but they could still fly. And we saw a northern gannet, a diving bird. It was oiled too,” she said. “I can only imagine that the birds left because the dining hall is closed.”

Soon, the rising towers of the Discoverer Enterprise drill ship, which is collecting oil and gas from the damaged well, and the tall rigs boring two relief wells miles into the seabed appear through the haze. A flare of burning natural gas is silhouetted against the gray hull of the ship.

The Premier Explorer, which is helping coordinate cleanup operations at the broken well, announces the day’s burn box: A 500-square-mile field within which 16 controlled burns will be conducted.

In the days since the April 20 explosion on the Deepwater Horizon, more than 5 million gallons of oil have been consumed in more than 165 burns.

“The real issue is to stop this thing at the source, do maximum skimming, in-situ burning — deal with it as far off shore as possible, and do everything you can to keep it from getting to shore, because once it’s into the marshes, quite frankly, I think we would all agree there’s no good solution at that point,” Coast Guard Adm. Thad Allen told reporters last week.

But the burn operations have proved particularly excruciating for the turtle researchers, who have been trolling the same lines of oil and seaweed as the boom boats, hoping to pull turtles out of the sargassum before they are burned alive.

Much of the wildlife here seems doomed in any case. “We’ve seen the oil covering the turtles so thick they could barely move, could hardly lift their heads,” Witherington said. “I won’t pretend to know which is the nastiest.”

Yet in one case, the crew had to fall back and watch as skimmers gathered up a long line of sargassum that hadn’t yet been searched — and which they believe was full of turtles that might have been saved.

“In a perfect world, they’d gather up the material and let us search it before they burned it,” Witherington said. “But that connection hasn’t been made. The lines of communication aren’t there.”

The smoke starts rising on the horizon at midday. The two boats carrying the researchers head in different directions, hoping to find and rescue a few more turtles before their mission wraps up. They find 11, all of them heavily speckled with oil.

Each day, the chances of rescues grow smaller. That there are still so many left stranded in the oil without food is a small miracle. Their long-term chances “are zero,” Witherington said.

“Turtles just take a long time to die.”

kim.murphy@latimes.com