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Oysters |
Oysters are a key component of the living ecosystem of Chesapeake Bay and its tributaries. They are important both ecologically and economically.
Ecologically, oysters pump water over their gills, removing organic and inorganic particles from the water column in which they live. This helps clear suspended material from the water, providing more light for aquatic grasses and benthic algae. Oysters also consolidate their feces or the non-food particles they reject into mucus-bound bundles that they expel back into the water column. This material is then available to be fed upon by other organisms living on the oyster reef. These reef organisms also take advantage of oyster shells, either as an attachment surface (e.g., barnacles, mussels, anemones) or as an environment for sheltering fertilized eggs while they develop (e.g., gobies, blennies). The nooks and crannies of the reef offer shelter to worms, clams, fish, and mud crabs. These organisms attract larger predators which in turn attract even larger predators. The existence of an oyster reef truly creates a dynamic environment. |
Click on photo for video on "Down on the Oyster Reefs"hosted by Maryland Sea Grant.
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Oysters are also important economically because they provide a market for food and a way of life for many watermen. Chesapeake Bay has long been one of the most productive oyster-growing areas in the world. At the end of the 1800’s it was estimated that over 15 million bushels of oysters were harvested annually from the Maryland portion of the Bay alone. The largely uncontrolled harvests that occurred during this exploitation period contributed to the destruction of the pristine oyster reef structures and began the downward trend in oyster populations and the industry that they once supported. During this decline, there were numerous efforts to rehabilitate the fishery.
Beginning in the late 1950’s and early 1960’s, diseases caused by two parasites (MSX and Dermo) became major impediments to restoring oyster populations in the Bay. Although MSX is limited to the saltier portions of the Bay, Dermo can exist just about anywhere oysters are found. Efforts to restore healthy oyster populations to the Bay’s once productive oyster areas are severely inhibited by these parasites. Restoration efforts in these areas are mostly focused on managing around the presence of disease. They are basically a “put-and-take” effort using pathogen-free young oysters (spat) and aimed at creating populations of oysters without disease. These populations must be monitored over time so that the onset of disease can be identified and corrective measures taken to remove parasites from the region. |
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Restoration Strategy
Horn Point scientists and their partners have made great progress in developing restoration techniques and have begun to experience successful restoration in some areas of Maryland. The restoration strategy underway at Horn Point Laboratory includes new and innovative approaches to oyster restoration that incorporate hatcheries and the specific pathogen-free oyster seed that they produce as an important tool for oyster restoration.
Not all restoration sites have the same goals or objectives. Some may be restored primarily for harvest, some for sanctuaries, and some for a combination of goals. Different goals require different restoration approaches, so strategies may change as new and better methods to achieve successful restoration are developed. The concept of managing oysters on a bar-by-bar basis rather than a State-wide basis is one that may become more important to successful restoration until a solution to oyster disease is reached. |
Click on photo for video on "Rebuilding the Bay's Reefs"hosted by Maryland Sea Grant.
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| One of the most innovative restoration approaches is that of “managed reserves”. Such reserves combine the benefits of having large concentrations of adult oysters that provide habitat for other organisms, filter water, and spawn successfully while at the same time making available oysters for market. To balance ecological benefits with economic benefits, managed reserves are designed to minimize the effects of Dermo on newly planted oyster spat by removing infected older oysters from the site before spat are planted on the site. Watermen help clean the bar of these adult oysters, which are either brought back to the hatchery for use as broodstock or are moved to an alternate location downstream where they can subsequently be harvested. Moving diseased oysters away from the site before parasite-free spat are planted helps delay infection by parasites and the spat enjoy greater growth and survival. Oysters are monitored as they grow and if parasite levels become threatening they may be harvested. If parasite levels remain below acceptable limits, the oysters are allowed to grow until the mean size of oysters on a site is 4 inches or more in shell height (this size is 1 inch larger than the size limit for oyster harvest in the Bay). Generally, it takes another year under good growing conditions for oysters to reach this larger size. This additional year is important in that larger oysters filter more water, spawn more gametes, and provide more shell substrate and habitat than do smaller oysters. |
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