Aug 9, 2010 8:59 AM by Sharlee Barriere

Crabs Provide Evidence Oil Tainting Gulf Food Web

BARATARIA, La. (AP) - To assess how heavy a blow the BP oil
spill has dealt the Gulf of Mexico, researchers are closely
watching a staple of the seafood industry and primary indicator of
the ecosystem's health: the blue crab.
Weeks ago, before engineers pumped in mud and cement to plug the
gusher, scientists began finding specks of oil in crab larvae
plucked from waters across the Gulf coast.
The government said last week that three-quarters of the spilled
oil has been removed or naturally dissipated from the water. But
the crab larvae discovery was an ominous sign that crude had
already infiltrated the Gulf's vast food web - and could affect it
for years to come.
"It would suggest the oil has reached a position where it can
start moving up the food chain instead of just hanging in the
water," said Bob Thomas, a biologist at Loyola University in New
Orleans. "Something likely will eat those oiled larvae ... and
then that animal will be eaten by something bigger and so on."
Tiny creatures might take in such low amounts of oil that they
could survive, Thomas said. But those at the top of the chain, such
as dolphins and tuna, could get fatal "megadoses."
Marine biologists routinely gather shellfish for study. Since
the spill began, many of the crab larvae collected have had the
distinctive orange oil droplets, said Harriet Perry, a biologist
with the University of Southern Mississippi's Gulf Coast Research
"In my 42 years of studying crabs I've never seen this," Perry
She wouldn't estimate how much of the crab larvae are
contaminated overall, but said about 40 percent of the area they
are known to inhabit has been affected by oil from the spill.
Tulane University researchers are investigating whether the
splotches also contain toxic chemical dispersants that were spread
to break up the oil but have reached no conclusions, biologist Caz
Taylor said.
If large numbers of blue crab larvae are tainted, their
population is virtually certain to take a hit over the next year
and perhaps longer, scientists say.
How large the die-off would be is unclear, Perry said. An
estimated 207 million gallons of oil have spewed into the Gulf
since an April 20 drilling rig explosion triggered the spill, and
thousands of gallons of dispersant chemicals have been dumped.
Scientists will be focusing on crabs because they're a
"keystone species" that play a crucial role in the food web as
both predator and prey, Perry said.
Richard Condrey, a Louisiana State University oceanographer,
said the crabs are "a living repository of information on the
health of the environment."
Named for the light-blue tint of their claws, the crabs have
thick shells and 10 legs, allowing them to swim and scuttle across
bottomlands. As adults, they live in the Gulf's bays and estuaries
amid marshes that offer protection and abundant food, including
snails, tiny shellfish, plants and even smaller crabs. In turn,
they provide sustenance for a variety of wildlife, from redfish to
raccoons and whooping cranes.
Adults could be harmed by direct contact with oil and from
eating polluted food. But scientists are particularly worried about
the vulnerable larvae.
That's because females don't lay their eggs in sheltered places,
but in areas where estuaries meet the open sea. Condrey discovered
several years ago that some even deposit offspring on shoals miles
offshore in the Gulf.
The larvae grow as they drift with the currents back toward the
estuaries for a month or longer. Many are eaten by predators, and
only a handful of the 3 million or so eggs from a single female
live to adulthood.
But their survival could drop even lower if the larvae run into
oil and dispersants.
"Crabs are very abundant. I don't think we're looking at
extinction or anything close to it," said Taylor, one of the
researchers who discovered the orange spots.
Still, crabs and other estuary-dependent species such as shrimp
and red snapper could feel the effects of remnants of the spill for
years, Perry said.
"There could be some mortality, but how much is impossible to
say at this point," said Vince Guillory, biologist manager with
the Louisiana Department of Wildlife and Fisheries.
Perry, Taylor and Condrey will be among scientists monitoring
crabs for negative effects such as population drop-offs and damage
to reproductive capabilities and growth rates.
Crabs are big business in the region. In Louisiana alone, some
33 million pounds are harvested annually, generating nearly $300
million in economic activity, Guillory said.
But fishermen who can make a six-figure income off crabs in a
good year now are now idled - and worried about the future.
"If they'd let us go out and fish today, we'd probably catch
crabs," said Glen Despaux, 37, who sets his traps in Louisiana's
Barataria Bay. "But what's going to happen next year, if this
water is polluted and it's killing the eggs and the larvae? I think
it's going to be a long-term problem."


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