our beloved crabs

are in danger

Louisiana blue crabs are tough, but Gulf oil spill might be tougher
Published: Tuesday, July 20, 2010, 10:29 PM Updated: Wednesday, July 21, 2010, 11:46 AM
Bob Marshall, The Times-Picayune

With their armored bodies and menacing pincers, Louisiana’s blue crabs were shaped by nature to be tough guys in the highly competitive coastal marsh. But evolution hasn’t prepared them for the test they’ll face during the next two months: The species’ peak spawning activities will take place where BP’s oil is most prevalent — the coastal beaches and near-shore Gulf.

Susan Poag, The Times-Picayune

“Forty percent of the most productive stations are within the confines of the oil spill,” said Vince Guillory, a biologist with the Louisiana Department of Wildlife and Fisheries, which manages a fishery that produces about 30 percent of the nation’s blue-claw crabs, a crop with a reported annual economic impact of $237 million.

“We are quite concerned that we will see significant mortality of larvae as they encounter oil or dispersants.”

Biologists aren’t expecting a wipeout, Guillory said. Like many estuarine residents, the so-called blue claw has become a fixture on the mean streets of the marshes because it is short-lived and extremely fertile; a single female typically will release 2 million to 3 million eggs and live for two spawning cycles. It doesn’t take many crabs to repopulate after a disaster, as long as the habitat base remains healthy and large, according to biologists.

But fisheries managers are concerned about long-term effects of the disaster on the species, because the estimated 200 million gallons of oil and millions of gallons of dispersants still out in the Gulf could be washing into crab habitat for years.

While state tests have yet to detect hydrocarbons in adult crabs, researchers have found oil in crab larvae coming into the estuaries. Other scientists fear contamination transferred to crabs through food sources could reduce their reproductive ability.

Since this type of disaster has never happened here, crab specialists aren’t really sure what to expect.

“As long as the habitat is in good condition, we’ll have good survivorship,” Guillory said. “But as long as the oil and dispersant is out there and coming to the shore, we’ll have mortality.”

Natural survivors

Nature seems to have equipped the blue-claw crab to cope.
Female blue claws mate only once in their lives, storing what will be a lifetime supply of sperm for future spawning. Fertilized eggs begin developing within weeks and are carried on the outside bottom of the female’s shell in a soft orange mass called a sponge.

As the eggs develop, the female crabs move to the southern end of estuaries looking for saltier water and offshore currents. Within two months of mating, fully developed eggs are released into the water as larvae called “zoeae” — microscopic creatures that resemble translucent spiders rather than crabs.

In Louisiana, some crab spawning takes place from April through October. But the nation’s richest blue-claw habitat really flexes its muscle in the peak months of July and August, when coastal beaches and shorelines near passes often seem to be literally crawling with sponge crabs.

This huge volume of larvae rides currents south into the open Gulf for miles, feeding on plankton for about 40 days, steadily growing by molting their exoskeletons and eventually growing into “megalops” – still less than a tenth of an inch wide, but now with tiny crab-like pincers.
“The megalops come back into the lower end of the estuary and gradually migrate into the northern end,” Guillory said.

Within three weeks, the surviving megalops have grown into juvenile blue-claw crabs, miniature replicas of the adults — and prime meals for the larger critters in the wetlands, such as redfish, drum, flounder and any number of birds. The blue claw prospers in that competition, in part, because of sheer numbers.

But the river of oil and dispersants BP has put into its world poses new, lethal threats during its most vulnerable period — the journey from egg to juvenile.

Facing a new threat

Biologists say exposure to the toxic components of oil and dispersants would almost certainly kill zoeae and megalops.
Scientists are also concerned about the detection of oil inside megalops by researchers at the Gulf States Marine Lab. Guillory said the state is awaiting the results of further study to see what, if any, impact that could have on the developing crab.

Jim Franks, fisheries biologist, and Read Hendon, assistant director at the Center for Fisheries Research and Development at the University of Southern Mississippi, bring in a sampling from their catch. The researchers are hoping to catch larvae stages of blue crab suspended in the water column to research the effects of the Gulf oil spill on the crabs.

And LSU researcher Richard Condrey has voiced concerns about hydrocarbon pollution transmitted to crabs through contaminated food sources in the estuary. Condrey said some toxins can accumulate in fats, which female crabs use to nourish their eggs.

The fear is that could reduce the fertility of female crabs, impacting the volume of future spawns.

None of that is certain, Guillory said, but neither can it be ruled out.
“There are a lot of questions we just can’t answer,” he said.
That is one reason scientists are collecting 28 samples of blue, stone and fiddler crabs a day, seven days a week, in Mississippi Sound, said Harriet Perry, director of the University of Southern Mississippi’s Center for Fisheries Research and Development in Ocean Springs.

Perry and her team of researchers were among those who found “bubbles” of hydrocarbon captured between the shell and inner skin of post-larvae crabs captured off Grand Isle last month.
Researchers have found similar bubbles in crab post-larvae in the sound since then.

“While we know the toxicity of Corexit (dispersant) and oil, nothing’s been looking at the two in combination,” she said. “We know invertebrates have a harder time with oil than the fish, which seem to just pass it through their systems.”

She hopes to continue to study the effects of the contamination to determine those long-term effects.

“Blue crabs are preyed upon by a whole host of fish species and each other,” she said. “So looking at the long-term ecological effect of the oil is important.”

The uncertainty has struck a note of fear for the future among crabbers, already beached by fishery closures forced by the oil.
“I’m not worried about this year. I’m worried about the next year and the years after that,” said Henry Martinez, who has crabbed the Delacroix wetlands most of his 72 years.

“Right now all the sponge crabs are out there trying to make babies, and that oil is killing the babies. So even when we can go back to crabbing, how many crabs will we have?

“No one can tell me that. And that’s what’s scaring me.”


~ by maringouin on Wednesday, July 21, 2010.

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