BARATARIA, La. -- 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 already had 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.
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 Laboratory.
"In my 42 years of studying crabs I've never seen this," Perry said.
While fish can metabolize dispersant and oil, crabs might accumulate the hydrocarbons, which could harm their ability to reproduce, Perry said in an earlier interview with Science magazine.
She told the magazine there are two encouraging signs for the wild larvae -- they are alive when collected and might lose oil droplets when they molt.
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. The spawning season occurs between April and October, but the peak months are July and August.
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.