Oysters, oysters, oysters!

Why are we so obsessed with oysters at Phillips Wharf? Well, oysters are delicious but they are also important residents of the Chesapeake Bay ecosystem and there are a lot fewer of them than there used to be.

 

Oysters are considered a keystone species. This means that places where oysters live are so dependent on those oysters that if they are removed, that area would look very different. This means that oysters have a huge impact on the environment in which they live. This includes their role as ecosystem engineers and filter feeders.

 

The term ecosystem engineer is used to describe species that literally build their environment around them. Beavers are ecosystem engineers because they use woody debris to manipulate the flow and retention of water, creating ponds where there used to be flowing water. Oysters are ecosystem engineers because they build reef systems simply by growing on top of other oysters’ shells. These oyster reefs are very important for many different species that call the Chesapeake Bay home.

 

 

Reef

 

Oyster reefs provide a hard structure for animals such as jellyfish (which have a stage of life where they stick to rocks and shells), bryozoans, and barnacles. In turn, these animals provide food for fish and other animals. The spaces between the oyster shells also provide habitat for fish and crabs and they provide a refuge from predators for juvenile fish, including many of the fish that make up important commercial fisheries. Without oyster reefs, the Chesapeake Bay would not be as good of a nursery for the many fish that come here to spawn.

 

In addition, oysters are filter feeders. This means that they actually clean water as they pull out algae to eat. Not only are they removing algae, but the other things floating around in the water that they don’t eat get packaged into “pseudofeces” and released, where it settles to the bottom of the Bay, instead of continuing to float around in the water. This helps reduce turbidity, which means it increases water clarity. This allows underwater grasses, which require sunlight, to grow in deeper areas of the Bay.

 

 

The problem is that the amount of oysters that remain in the Chesapeake Bay are approximately 0.3% of what existed in the 1700s (Wilberg et al. 2011). Even worse, the Maryland Department of Natural Resources has reported that the population of oysters in the Chesapeake declined by 50% from 1988 to 2018 (Maryland DNR, 2018). This means we likely have even less than 0.3% of historic oyster population levels in the Chesapeake Bay, even with millions of dollars of funding being poured into oyster restoration.

 

While that may make oyster restoration seem pointless, the fact that oysters still exist in the Chesapeake and that they are still reproducing in the wild, means that we have a chance at saving them and that our work has not been in vain. 

 

The Phillips Wharf Environmental Center is one of many different groups and organizations working to help restore oyster populations. We do this in several ways; the first is through our oyster growing program, Tilghman Islanders Grow Oysters. The second is through our oyster aquaculture business, Fisherman’s Daughter Brand Oysters.

 

Through our Tilghman Islanders Grow Oysters program, volunteers offer to host oyster cages to hang from their docks for 9 to 10 months. During this time, young oysters grow large enough to be better protected from predation; when small, their shells are thin and brittle, but as they grow in size, their shells grow stronger. By growing the oysters in cages, it is also very simple to rinse them off by pulling the cages up and dunking them in the water a few times before rehanging them. This helps prevent the oysters from suffocating when too much sediment settles on them after rain events. After the 9 months or so are up, we collect the cages and plant the oysters on existing oyster reefs in the Chesapeake Bay, essentially adding these grown oysters to wild populations.

 

 

Since we began TIGO in 2011, we estimate that we have planted over 760,000 oysters in and around Harris Creek. While most, if not all, of these oysters have been planted in the Harris Creek Oyster Sanctuary, we are looking to expand where we plant oysters to include public oyster grounds. While the oysters planted in the sanctuary should theoretically have a longer life than oysters planted where they can be harvested as soon as they are market size, we believe that supporting the commercial fishery is also valuable.

 

 

The idea here is that commercial fishing, including oysters, makes up a large portion of Maryland’s economy. In addition, oystering is part of the cultural heritage of the Eastern Shore. The need to have boats that could tow a large dredge over shallow oyster reefs is why skipjacks were developed and these boats are quintessential pieces of Chesapeake Bay history. By planting oysters on public grounds, we are supporting the continuation of the waterman way of life and an essential piece of local tradition.

 

It’s also important to remember that oysters are always filtering the water, regardless of where they are. Even as young oysters hanging from a volunteer’s dock, they are filtering water. Regardless of where they are planted, they are filtering water. This is also why oyster aquaculture can be an important part of a healthy Chesapeake Bay; the oysters grown on leases with the intention of ending up on your dinner plate are still filtering the water before they are harvested. They also serve as valuable habitat for a variety of organisms. When we pull up cages on our farm, we see many different species of fish, crabs, and shrimp.

Skipjack

 

Oyster aquaculture also serves to support the market for commercial oysters while lessening the demand on wild populations. Recent research also suggests that if aquaculture oysters are harvested over relatively short timescales, they can actually help reduce disease in wild populations (Ben-Horin et al. 2018). This is because the aquaculture oysters pick up the disease causing organisms, thereby removing them from the water and preventing them from infecting wild oysters. This is particularly relevant to Dermo (Perkinsus marinus), which can take up to three years to kill an oyster once it becomes infected. Once the oyster is dead, it releases more parasite cells into the water, thus spreading the disease to nearby oysters (Calvo et al. 2003). If oysters are instead harvested before the infection progresses, these oysters act as a sponge, absorbing and removing disease causing organisms from the water column. 

 

This is also true for oysters that are planted on wild oyster reefs and are eventually harvested, but it is not true for oysters that are planted in sanctuaries. Because these areas are protected from harvest, oysters that get sick stay in the water and can spread disease. In fact, scientists have observed that up to 90% of all older oysters (>7 years of age) in sanctuaries throughout the Chesapeake Bay are infected by P. marinus (Paynter et al. 2010).

 

Ultimately, we believe that the more oysters we can put in the Chesapeake Bay, the better. We believe in oyster restoration that supports a healthy Chesapeake Bay and a strong economy and we think programs like Tilghman Islanders Grow Oysters can do both. If you want to support our work, donations can be made by check (include TIGO in the memo line and mail to Phillips Wharf Environmental Center, P.O. Box C, Tilghman, MD 21671) or online here. You can also support our work by purchasing Fisherman’s Daughter Brand Oysters here.

 

 

References:

Ben-Horin, T., Burge, C. A., Bushek, D., Groner, M. L., Proestou, D. A., Huey, L. I., ... & Carnegie, R. B. (2018). Intensive oyster aquaculture can reduce disease impacts on sympatric wild oysters. Aquaculture Environment Interactions, 10, 557-567.

 

Calvo, L. M. R., Dungan, C. F., Roberson, B. S., & Burreson, E. M. (2003). Systematic evaluation of factors controlling Perkinsus marinus transmission dynamics in lower Chesapeake Bay. Diseases of aquatic organisms, 56(1), 75-86.

 

Maryland Department of Natural Resources. 2018. A stock assessment of the Eastern Oyster, Crassostrea virginica, in the Maryland waters of Chesapeake Bay. Final Report November 2018. 359 pp <https://dnr.maryland.gov/fisheries/Documents/StockAssessment_EasternOysterMD.pdf>

 

Paynter, K. T., Politano, V., Lane, H. A., Allen, S. M., & Meritt, D. (2010). Growth rates and prevalence of Perkinsus marinus in restored oyster populations in Maryland. Journal of Shellfish Research, 29(2), 309-317.

 

Wilberg, M. J., Livings, M. E., Barkman, J. S., Morris, B. T., & Robinson, J. M. (2011). Overfishing, disease, habitat loss, and potential extirpation of oysters in upper Chesapeake Bay. Marine Ecology Progress Series, 436, 131-144.