June 14, 2010
Researcher narrows down spread of first lobster virus
From the Florida Keys to Cuba to the Bahamas and Belize, tourists and locals enjoy the taste of the Caribbean spiny lobster. Family operations and commercial fisheries alike depend on its popularity, so the lobster is important to many local economies.
But this crustacean is threatened by a virus called Panulirus argus virus 1 (PaV1).
"We know that it can spread between lobsters. They can eat infected tissue and contract it that way, or get it through contact with other lobsters," says Donald Behringer, marine ecologist at the University of Florida.
According to Steve Otwell, professor of food science and human nutrition at the University of Florida, there's no scientific evidence of a similar threat from the PaV1 virus to humans. "The information we have available suggests that this virus is very host specific," he says.
Behringer was studying lobster density in 1999 when he discovered a number of sick animals. The lobsters became lethargic--they stopped molting and stopped eating. Infected animals took on a pinkish, cooked color. "We ultimately discovered what turned out to be the first virus for any lobster in the world," says Behringer.
He finds with PaV-1, the animals appear to be dying of "metabolic exhaustion." They cannot oxygenate their tissues, their tissues deteriorate and they die. "Probably 95 percent of those that become infected with it die of it," he notes.
The level of infection is believed to be between five and eight percent of the population. Behringer is now using a grant from the National Science Foundation (NSF) to try to understand the dynamics of the disease, and specifically how it's spreading. "We see it pretty much everywhere we've looked in the Caribbean," he says.
And, it now looks like the lobsters' larval stage may provide some answers. Spiny lobsters have a larval period that lasts from six to eight months. During that time, the larvae are circulating out in the ocean currents.
"So really, it is that larval stage that connects all these places in the Caribbean," explains Behringer. "There's really no precedent for this theory that larvae are acting as uninfected vectors of disease, literally taking it from the adults and taking it right into the juveniles which is the most susceptible population."
Behringer notes that this particular transmission vector has never been seen before with marine animals, and it could explain how the virus has turned up in so many places, from Florida to the Caribbean to Mexico, in such a short period of time.
The international aspects of the disease make it even more complicated to study and manage. Each country has different regulations for commercial and sport fishing.
Behringer says, so far, he and his colleagues have met with cooperation from both government agencies and those who make their livelihood from the seas. Scientists in several countries have sent sample tissues, and fishermen have allowed Behringer to join them on their boats while they're checking traps.
"Our motivation is not to put them out of business, but to make sure that what they are doing is sustainable, for them, for the creature, for the ecosystem," he says.
A better understanding of how the virus spreads could lead to more effective management strategies for protecting uninfected lobsters from getting the disease.
At his lab at the University of Florida in Gainesville, Behringer and graduate student Josh Anderson showed another unusual aspect of the disease.
These lobsters appear to have "disease detectors" that keep some of them from getting sick.
"They are literally tasting the water when they flick their antennae," says Behringer. "They can smell one another, they can smell food, and we think they can smell disease as well. And they can do so before that diseased lobster becomes infectious to them. So it seems to be a very adaptive mechanism of reducing their potential for infection," he explains.
Anderson had set up two tanks, one with a sick lobster, one with a healthy one, each with a tube leading a couple of feet below to a wooden maze with one healthy lobster in it. When released, the lobster in the maze very quickly scurried toward the water coming from the healthy lobster's tank.
"It appears that, as we hypothesized, they are avoiding the scent of a diseased lobster," says Behringer.
Marine scientists are looking at other factors that may be spreading the virus.
"We'll be looking to see if ocean warming might be why we are seeing an increase in prevalence in this disease. Maybe it's something that has always been endemic to the population at very low levels, and that it may have risen to high enough levels to where we've started seeing it," he says.
"As far as global climate change, increasing water temperature, decreasing water pH, ocean acidification, what effects do those have on the viability of the virus?" he asks.
Behringer says his research is important on a lot of levels, among them, to give some insight about how diseases work in the marine environment, and also to help an important industry.
"This is an organism that is the most economically important in all of the Caribbean," he says.
The work is also a very physical job. Behringer spends time diving, doing research in the field, writing and teaching.
"There's no monotony. It's very dynamic. It's a dream career as far as I'm concerned," he says.
Any opinions, findings, conclusions or recommendations presented in this material are only those of the presenter grantee/researcher, author, or agency employee; and do not necessarily reflect the views of the National Science Foundation.