Oil plumes invade a dark, mysterious world at Gulf's floor

Oil plumes invade a dark, mysterious world at Gulf's floor
By ANDRES VIGLUCCI
McClatchy Newspapers

Deep beneath the Gulf of Mexico lies a dark and frigid world surprisingly abundant in otherworldly forms of life, much of it fed by gases and oil that seep out of fissures in the sea floor. Here on the sea floor, at near-freezing temperatures and crushing depths that can reach 9,000 feet, are methane-munching bacterial mats; mussels the size of a big man's foot; tube-shaped animals that grow 10 feet long and live more than 250 years, and expansive beds of coral that thrive in total darkness. Much of this life was utterly unknown until the dawn of deep-sea oil exploration in the early 1980s, which led the federal government - and in particular the Minerals Management Service, the agency now under fire for lax supervision of deepwater rigs - to finance extensive scientific investigation of the bottom of the Gulf.
Since then, scientists who deploy robots to the sea floor or plunge into the depths in miniature subs have documented the existence of dozens of scattered communities of tentacle-like, hydrocarbon- sucking tubeworms and giant mussels and clams clustered around seep sites, as well as dramatic coral habitats some believe may be feeding grounds for deepwater grouper and other large species of fish.
"Most of the Gulf of Mexico is muddy bottom. If you go down to the sea floor in a submarine, what you will often see is mud, with the occasional crustacean," said Charles "Chuck" Fisher, a marine biologist at Penn State who has conducted pioneering research into the Gulf's deepwater ecosystems. "When you come up on a seep site or a coral site, it's spectacular. There are literally thousands to hundreds of thousands of animals at one time."
Much about these strange animals and their relationships remains unclear, including the function of the iceworms Fisher discovered encrusted in frozen methane mounds on the sea bottom in the late 1990s. New species are discovered on nearly every dive.
But the scientists who study the Gulf bottom are alarmed over the potential for catastrophic effects on the fragile seafloor ecosystems from the underwater oil plumes billowing for miles from the site of the Deepwater Horizon rig explosion.
"Unfortunately, there's really no place for this oil to go where it won't have a negative impact," said James Cowan, a professor of oceanography at Louisiana State University who has recorded plumes of oil 400 feet beneath the Gulf's surface. At this point, the scientists can offer little more than reasoned speculation. No one has yet gone deep to test for the effects of the oil spill because deep-sea ventures are expensive and must be planned well in advance.
Florida Atlantic University's Harbor Branch Oceanographic Institute hopes to send out its four-person submersible, the Johnson-Sea- Link, to examine deepwater coral communities off the Florida coast by the end of the month.
The deepwater corals, which live in depths from a few hundred to thousands of feet, may be particularly vulnerable, Cowan and others say. Given the lack of light, those corals do not use photosynthesis to produce their food like their shallow-water cousins do. The deepwater coral instead rely for nutrition on organic material that drops like snow from the water column, including tiny shrimp and copepods, as well as dead matter and crabs, fish and corals in their larval stages, said John Reed, a research scientist at Harbor Branch who has made scores of dives to the Gulf seafloor. Some researchers suggest the deep-sea coral may have adapted to the oil that naturally flows across Gulf waters from the natural seeps deep below.
But Reed and Cowan, among others, fear the plumes from the Deepwater Horizon could smother them. Tiny globules of toxic oil could also enter the food chain, contaminating it as the material falls on the reefs, Reed said.
"It would kill them. It would essentially be food poisoning," he said.
Chemical dispersants mixed in with the oil in the plumes could make matters worse, although no one has any idea what the precise effects will be. The government has not funded any studies on the impact of dispersants on the Gulf ecology.
"We don't know toxic how those dispersants are," said Gregor Eberli, a marine geologist at the University of Miami. "We know absolutely nothing." In the worst case, miles of deepwater coral - and the habitats and biological diversity they represent - could be wiped out, scientists say.
"They grow very very slowly, less than a half-inch a year, so if they get destroyed they may never come back, or it could be centuries before they do," Reed said.
Less obvious is what might happen to the complex communities of inter-dependent tubeworms, bacteria, shellfish and crustaceans that live around cracks in the ocean floor through which oil and other energy-rich fluids bubble up from underground petroleum deposits. Most are strung along the northern Gulf, in areas where oil-drilling platforms have proliferated.
Here the fauna survive thanks to co-dependent, or symbiotic, relationships: The tubeworms, which are anchored to sediment on the bottom, suck up gases like methane and hydrogen sulfide from the cold seeps, where temperatures are just a few degrees above freezing. Bacteria living inside the tubeworms - and in the gills of mussels - consume the gases, producing carbon to feed their hosts and also themselves. The process is called chemosynthesis.
Free-living bacteria, meanwhile, process the hydrocarbons to produce rock on which other species can proliferate, some feeding on the bacteria. The communities, Penn State's Fisher said, are long-lived, probably lasting centuries.
"There's literally 100 other species feeding on bacteria as well as each other, like shrimps and snails," he said.
The particular species vary by depth, with a complete turnover occurring below 3,000 feet, he said.
Scientists say the cold-seep communities are similar in many ways to those found at hot, or hydrothermal, vents discovered in the 1970s in the Pacific and Atlantic oceans, where the earth's tectonic plates meet, releasing superheated gases. But no one thought anyone would find much of anything when the start of oil exploration in the Gulf sent scientists to find out what might live beneath. In 1984, Texas A&M scientists on an exploration cruise in the central Gulf trawled the bottom with a net, expecting little to come up, Fisher said.
Instead, Fisher said, "the net was so full of animals they had a hard time getting it on board the ship." By then, the manned submersible DSV Alvin had discovered numerous such communities in the eastern Gulf, and as finds multiplied, the MMS enacted some basic protections, though scientists fear those may now prove inadequate.
Under the rules, no drilling is allowed directly over deepwater seep and coral communities, and rig anchors and activity is kept at least 1,500 feet away.
One of the best-known cold-seep communities, named Bush Hill by researchers because of its thickets of tubeworms, sits 500 yards from a deepwater well.
But extensive environmental impact studies prepared by MMS indicate the agency never seriously considered the potential impact of explosions or oil gushing out of deepwater wells on such habitats.
"Impacts to chemosynthetic communities from any accidental release of oil would be a remote possibility. The rarer, widely scattered, high-density, Bush Hill-type chemosynthetic communities could experience very minor (if any) impacts from drilling discharges or resuspended sediments located at more than 1,500 feet away," the MMS concluded.
What MMS failed to account for, scientists say, are the oil plumes, some of them miles long, that have been documented drifting across the Gulf from the Deepwater Horizon site.
Last month, University of Southern Mississippi scientists aboard a research vessel found oil plumes as long as 10 miles long and three miles wide. The shallowest plume was at 2,300 feet deep, while the deepest plume was near the seafloor at about 4,200 feet - prime cold-seep depth.
Although the tubeworms and other creatures in cold-seep communities do consume oil and hydrocarbons, they do so in a delicate balance and may be unable to absorb a spike in the supply. As to the effect of dispersants on seep communities, those are totally unknown as well, scientists say.
Almost certainly, Fisher said, the tubeworms at the center of cold-seep ecologies will not benefit from a sudden increase in hydrocarbons in the water. He fears oil globules could clog tubeworm feeding appendages.
"Whether the concentrations are high enough to hurt them is another question," Fisher said. "But as a general rule deep sea animals are adapted to a stable environment ... a certain temperature, a certain flow of hydrocarbons. In some ways, they are less adapted to insults. There are certainly scenarios that could lead to serious effects."
What could be lost: A set of diverse and unique species, and possibly important clues to the origin of life on earth, said LSU's Cowan. "A lot of people now believe this is the place where life first formed on earth, and we're just in the process of cracking that egg," Cowan said.
McClatchy Newspapers reporters Scott Hiaasen and Stephanie Genuardi contributed to this article.