Protecting Oysters from Burrowing Shrimp

For members of the multimillion-dollar West Coast shellfish industry, their world is the oyster.

Unfortunately, the oyster industry's ability to meet rising demands is hampered by two species of burrowing shrimp. So Agricultural Research Service (ARS) scientists are collaborating with colleagues from Washington State University and Oregon State University to develop sustainable shrimp-control strategies.

Ghost shrimp and mud shrimp inhabit the tideflats in estuaries where West Coast oysters are raised. The shrimp burrow into the estuaries, making the intertidal mud soft and unstable. As a result, oysters and other shellfish can sink beneath the silty surface and suffocate.

Brett Dumbauld, an ARS ecologist stationed in Newport, Ore., and his colleagues are uncovering information about the shrimps' habitats, life history and natural predators—information that can be used to help develop new methods to protect oysters from pests.

The scientists showed that ghost and mud shrimp may be most vulnerable to control directly after "recruitment," when an influx of young shrimp enters the estuaries. At this point, the shrimp live in small burrows near the surface, where they are potentially more vulnerable to predators and other treatment measures.

Dumbauld examined several shrimp populations in Washington and Oregon estuaries and observed wide fluctuations in the number of young shrimp returning each year. This is significant because being able to predict high recruitment could impact the effectiveness of control strategies by improving the timing, intensity and targeting of treatment.

Dumbauld is also collaborating with scientists at the U.S. Environmental Protection Agency's Pacific Coastal Ecology Branch to create maps that will help scientists determine how shrimp populations are distributed and whether control measures can be more effectively deployed on a large scale. This type of information is critical to developing successful integrated pest management strategies.

In a related study, Dumbauld and Tony D’Andrea, an assistant professor at OSU, worked with OSU graduate student Katelyn Cassidy to examine the amount of lipofuscin—an aging pigment—in the shrimps’ neural systems.

From this information they can estimate the age of the shrimp. Age can then be combined with historical data collected from shrimp populations and compared to historical patterns in weather and currents to determine how these oceanographic variables influence movement of shrimp larvae and recruitment to estuaries.

“This information could be used to develop predictive tools for targeting and controlling shrimp at the recruitment stage and for using alternative mechanical, biological, and perhaps even less-toxic chemical controls that don’t work for adults but might be more effective for young shrimp,” Dumbauld says.

Parasite Power

Dumbauld is also collaborating with scientists at the U.S. Environmental Protection Agency’s Pacific Coastal Ecology Branch. They’re using aerial photographs to create maps of the areas inhabited by the oysters and shrimp in Willapa Bay, Washington—one of the nation’s biggest producers of farmed oysters.

“This will enable us to examine the effects of aquaculture practices, including shrimp control, at the landscape scale,” Dumbauld says. “The ultimate goal is to develop best-management practices for aquaculture in these estuaries.”

The maps will help scientists determine how shrimp populations are distributed and whether control measures can be more effectively deployed on a large scale. This type of information is also critical to developing successful integrated pest-management strategies.

Another application of the information could be examining the distribution of marine predators that may influence the survival and distribution of shrimp. For example, one species of mud shrimp is highly infested with an isopod parasite, Orthione griffenis, or Griffen’s isopod.

The parasite sucks the shrimps’ blood, depleting their energy levels to the extent that they can no longer reproduce. Infested populations suffer significant reproductive declines—as much as 85 percent in some locations. It appears that this loss of reproductive capacity has caused the mud shrimp populations to collapse in some estuaries.

Dumbauld is working with John Chapman, an OSU professor, to investigate the dynamics of this parasite-host relationship and to determine whether a related parasite could be used to control ghost shrimp populations.

These studies lay the foundation for sustainable practices that will support the growth of the West Coast oyster industry.