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Oyster restoration efforts continue in Chesapeake Bay - April 9, 2013

In 1608, John Smith started mapping the Chesapeake Bay. However, it was very different from today’s bay; the water was cleaner, the diversity of animals astounding and the landscape dominated by forests and marshes. Huge oyster reefs were plentiful throughout the bay and made navigation for Captain Smith difficult, leading to him remark that the oysters “lay as thick as stones.”

Flash forward nearly 400 years and the story is completely different. Oyster populations have been decimated. Overharvesting, diseases and poor water quality have led to a sharp decline in oyster populations. However, there are many dedicated people and organizations encouraging the resurgence of the oyster.

In oyster hatcheries like Horn Point Lab, the future of our oyster population is being born and raised. Mature oysters will release sperm and eggs in a tank. The eggs become fertilized and are then moved to another tank, where they will grow into veligers. The veliger phases are the only phases in an oyster’s life cycle where it is at least partially ­mobile.

The oyster will go through several veliger phases before eventually turning into a pediveliger, which has a muscular foot, similar to a clam, which allows it to crawl. At this point, the pediveliger will be placed into a different tank where weathered oyster shells have been placed. The pediveliger will eventually settle onto these old shells and mature into spat on shell.

Once the spat establishes itself, it will no longer be mobile and will start to mature into an adult oyster. The entire process, going from free-floating sperm and egg to settling down and turning into spat on shell, takes anywhere from two to three weeks. Once the spat is established, it can take one to three years for it to turn into a mature oyster capable of reproduction. Mature oysters can live for decades in the right conditions, and during this time they can even switch genders if needed for ­reproduction.

Oysters in the bay are a keystone species. Not only do they filter the water, but they also provide much needed habitat for many species of animal. Oyster reefs are one of the few areas of hard substrate on the bottom of the Chesapeake Bay. They provide places for other benthic organisms to live, and also provide shelter and food for larger fish.

Estimates put upwards of 90 percent of our historic oyster reef habitat as lost, and the remaining oyster reefs are diminishing due to severe stress.

In order to restore these important habitats and increase oyster populations, the state has partnered with a variety of organizations and agencies to create protected oyster sanctuaries.

Oyster sanctuaries are areas that are used for oyster restoration projects where shellfish harvesting is permanently closed. The Maryland Department of Natural Resources, National Oceanic and Atmospheric Administration (NOAA) and Marylanders Grow Oysters have all been involved with setting up, maintaining and patrolling these new oyster sanctuaries.

Oyster sanctuaries have to be placed in very specific locations. Oyster spat needs a hard substrate to grow on, preferably old oyster shells, so oyster sanctuaries need to be placed in areas with hard bottom substrates. Currently, sanctuaries are set up in multiple tributaries of the Chesapeake Bay including the Nanticoke, Choptank, Chester, Severn and Patuxent rivers, along with several large areas in the bay itself.

By spreading the sanctuaries throughout the bay, researchers can look at how salinity levels effect spawning and disease. We know that oysters reproduce better in higher salinity water; however, diseases such as DERMO and MSX are more active in higher salinity water. This means that we have to find a balance between reproductive effectiveness and the risk of disease.

One of the biggest problems posed to oyster restoration work is the illegal poaching of oysters from sanctuaries. This illegal harvesting is a problem because it interferes with research in the sanctuaries and weakens the restoration efforts due to oyster population loss. It can also be dangerous because many of the sanctuaries are in tributaries with poor water quality, meaning the oysters are not safe to eat.

So far, oyster restoration efforts have been slowly bringing back the oyster population in the bay, but there is still much more work to be done before this valuable shellfish has made a full ­recovery.
 

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