University of Maryland Center for Environmental ScienceHorn Point Oyster Hatchery

Oyster History

The Chesapeake Bay has long been considered 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 Chesapeake Bay alone. The largely uncontrolled oyster harvests that occurred during this exploitation period contributed to the demise of the pristine oyster reef structures and the trend of Chesapeake Bay oyster decline. Unfortunately the Chesapeake Bay oyster decline continued and has contributed to the degradation of the Bay’s health and of many industries it supports.

Classic Oyster Tonging

The Impact of Oyster Disease

More recently, two parasites (MSX and Dermo) have invaded the Chesapeake Bay Oysters with devastating results. Beginning in the late 1950’s and early 1960’s these diseases have spread up Bay until almost no oyster populations remain unaffected. MSX is limited by salinity to the saltier portions of the Chesapeake Bay. Dermo can exist just about anywhere oysters are found.

Chesapeake Bay Oyster restoration efforts to restore once productive oyster areas are severely inhibited by these parasites. While similar in results, the diseases behave differently. MSX can infect oyster populations and quickly result in the death of young oysters (spat). Dermo infections usually have a longer incubation period before oysters start to die. Oysters typically become lightly infected with the dermo parasite during the late summer or fall of one year. It takes another summer or two (depending upon conditions on the oyster bar) for the infection to become intense enough to cause the oysters to die.

Oyster restoration projects located in high salinity areas, where both MSX and dermo are present, have proven problematic. Exposing oysters to intense disease pressure in the hopes of developing a more disease resistant oyster has received some support in recent years. The likelihood that this will become successful in any reasonable time frame is slim due to the numbers involved.

Oyster restoration efforts in areas where salinity is lower and MSX is not present also come with its own set of problems. Dermo can cause large numbers of mortalities depending upon conditions on a particular oyster reef. Periods of drought bring higher salinity levels and more virulent impact from Dermo. Restoration of oysters in these areas is more about managing around the presence of disease. Until an effective strategy has been proven, restoration efforts will likely be more of a put and take effort aimed at creating populations of oysters without disease.These populations will be monitored during the grow-out period so that the onset of disease can be identified and corrective measures taken to remove parasites from the region.