October’s Chesapeake Bay spotlight is a favorite of fish and people alike – oysters! October signals the start of the oyster harvest season here in Maryland that runs through the winter into March. Harvesting is avoided in the summer since that’s when they spawn, and it’s important to set aside that time for the population to replace itself and hopefully grow.
The Eastern oyster (Crassostrea virginica) is the native species found along the Atlantic Coast and is typically the one that you can find on the menu at a local seafood restaurant, even if they have different descriptions (like blue points, Choptank sweets, etc.). In the wild, oysters are just as important of a food source for fish and other animals as they are for us. One of their main predators is Maryland’s own blue crab.
Oysters are only able to swim during the early stages of their life. Oysters are in their motile larval stage for a couple weeks, after which they become what we call ‘spat’, young oysters that attach themselves to a hard surface and stay that way for the rest of their lives as they grow. This hard surface could be a rock, or commonly another oyster shell [1]. From this stage they grow their shells continuously through their adult lives.
One of the major impacts of oysters in the Chesapeake Bay comes from the tendy of oysters to grow on top of each other, which creates hard substrate on the normally muddy bottom of the Chesapeake Bay. This substrate becomes habitat for a wide variety of species and is the foundation of an oyster reef. Oyster toadfish, mudcrabs, and skilletfish are just some of the species that you could find swimming or crawling around an oyster reef. Without the shelter that oyster shells provide, many of these species would be much more vulnerable to larger predators.
Oysters eat phytoplankton (tiny plants) that drift through the water column. They are filter feeders, which means they open their shells and pump water through their gills, trapping food and other particles along the way. Non-food particles are cleared through psuedofeces, which the oysters then ‘spit’ out. You can click on the video to the right (made by Dr. Matt Grey at Horn Point UMCES) to see just how oysters do this.
The oyster population in the Chesapeake Bay today is a fraction of what it used to be. There are a multitude of causes for this including overharvesting. At the turn of the millennium the oyster population in the Bay halved due to overharvesting in an already declining population, a major blow to not only the oyster population but the Bay ecosystem as a whole [2]. Diseases are another major threat to oysters today, there are two major ones called Dermo and MSX. Dermo is a parasite that attacks the blood cells of oysters and thrives in warmer waters, so it has become an increasingly strong threat as water temperatures warm. MSX is a disease that prevents and alters the feeding habits of oysters until they pass from lack of nutrition [2]. MSX also tends to prefer saltier water, so it is more prevalent in Virginia waters, while Dermo prefers mid-range salinity and is more prevalent in Maryland waters.
That being said, in the last decade the Chesapeake Bay oyster population has rebounded significantly, starting at about 1 billion in 2017, it is now at 7.6 billion from recent 2025 data [3]. Restoration efforts have made significant progress, but even with that the oyster population is nowhere near historic numbers, and the threat of disease continues to fight those efforts.
A common question regarding oysters is whether or not they make pearls and the answer is yes! The pearls they form, however, are not as bright and shiny as a pearl one might immediately think of. Instead, they’re darker and a more brownish green color, almost like a booger. This makes their pearls less desirable to most, however they’re just as rare as any other naturally occurring pearl.
References:
[1] https://www.chesapeakebay.net/discover/field-guide/entry/eastern-oyster