VIMS scientists to study blue-crab disease
Professor Jeffrey Shields of the Virginia Institute of Marine Science,
College of William and Mary, has received a five-year, $2.4 million
federal grant to study how fishing pressure and declines in water
quality affect the emergence and spread of a blue crab disease in the
seaside bays of Virginia's Eastern Shore.
The grant is one of only eight such awards made to research teams
nationwide. It comes through the Ecology of Infectious Diseases (EID)
Program, a joint effort of the National Science Foundation (NSF) and
the National Institutes of Health (NIH).
Shields is joined on the project by VIMS researchers Kimberly Reece and
Harry Wang, along with Dr. Mark Butler of Old Dominion University. The
grant supports three newly hired post-doctoral fellows and three
graduate students at VIMS as well as a graduate student at ODU.
Shields notes that fishing pressure is known to affect the movement,
aggregation, feeding, and mortality of marine organisms, and therefore
the transmission of disease. Despite this, he says, "The effect of
fishing pressure on disease has received little attention."
Shields and his team will use the grant to study how fishing pressure
and declining water quality within coastal bays may promote outbreaks
of Hematodinium in blue crabs. Hematodinium is a parasite that infects
the blood of crabs and other crustaceans worldwide.
In blue crabs, Hematodinium outbreaks are most common in fall among
juveniles within the relatively warm, salty waters of coastal bays
along the Atlantic seaboard, particularly in Virginia, Maryland,
Georgia, and Florida. Hematodinium was first reported from the Eastern
Seaboard in the mid 1970s. The first Virginia outbreak was reported in
1994.
Shields suspects that trapping of water within these shallow bays
amplifies the parasite's spread, thus leading to seasonal outbreaks of
the disease in blue crabs. He also suspects that the blue-crab fishery,
by targeting adults, increases the relative number of juveniles, which
are more susceptible to the parasite.
During disease outbreaks, crab mortality can reach 50% in crab pots,
and 75% in shedding facilities on Virginia's Eastern Shore. Infections
are generally fatal with crabs dying from energy depletion or
disruption of bodily tissues. The disease is not harmful to humans.
Shields estimates that Hematodinium outbreaks cost Virginia's blue crab
fishery from $500,000 to $1 million in losses per year. By
investigating how the parasite is transmitted and causes disease,
Shields's study may help reduce these losses by identifying how fishing
practices may promote disease transmission in coastal bays.
"Anecdotal evidence suggests that some fishing practices may help to
spread the disease," says Shields. "These include culling of the catch
between locations, re-baiting with infected animals, and in some cases
using male crabs as bait to attract pre-molt females for the soft-shell
fishery."
Shields notes that the results of his team's study will have
far-reaching implications. "While we are focusing on a protozoan
disease in the blue crab, our work has broad application to other
fisheries. We see the blue crab-Hematodinium system as a general model
to gauge how fishing, by removing adults, affects the spread of
diseases most prevalent among juveniles. Few if any studies have
produced models capable of integrating local environmental change and
fishing pressure with disease dynamics for mobile marine organisms.
This has broad application to several fish and shellfish populations."
James Collins, Asst. Director for Biological Sciences at the National
Science Foundation, one of the federal agencies supporting Shield's
work, echoes Shield's assessment of the study's broader significance.
Says Collins, "Understanding the causes and consequences of emerging
infectious diseases is among the grand-challenge questions in the
environmental sciences."
Discover more about the work at the College's Virginia Institute of Marine Science at www.vims.edu.