Crassostrea virginica, the American oyster, is a native icon to the Chesapeake Bay. It is important to this region in a variety of ways- historically, economically, culturally, and ecologically. The Native American name for the Chesapeake actually means “great shellfish bay”, and oysters have been harvested from its waters ever since man inhabited the shores. These mollusks are a source of income and way of life for many people in the region, and have been for centuries. This bivalve creature with a stationary life is also especially important to the ecology of the Chesapeake. As a filter feeder, it has the ability to cleanse the water of phytoplankton, or algae, and it also serves as habitat and a source of food for other animals (Connaughton, “Shallow Seas”). The Chesapeake Bay is a complex ecosystem, and so is the oyster, as well as its past, present, and future fates. Issues related to them are very involved and debatable, creating many different viewpoints and opinions.
Commercial harvesting of oysters has had a large presence on the Chesapeake Bay for quite some time. Starting in the late 1800’s, over-harvesting caused the Bay’s oyster population to decline severely. Oysters have been decreasing in numbers since then, and the population is now estimated to be less than 1% of what it was historically. This decline has been due to several additional factors including diseases such as MSX and Dermo, as well as sedimentation and low-salinity events. Now, along with a dwindling oyster population, the Bay faces other issues, one of which is eutrophication. The nutrients nitrogen and phosphorous are entering from land-based sources- such as industry and agriculture- into the Bay’s waters in excessive amounts and fueling the growth of algae to an extent that it causes major problems. A lot of algal growth blocks out sunlight from reaching the bottom of the Bay, and impairs the growth of underwater grasses. Fewer grasses results in a lower amount of oxygen being put into the water, causing dead zones- hypoxic (low-oxygen) or anoxic (no-oxygen) areas of water. This is further exacerbated by the fact that decomposers consume a lot of oxygen as the excess algae dies off. As a result, increasing dead zones have meant a great loss of habitat for many organisms in the Bay, and have affected other populations, such as waterfowl. However, the effect of eutrophication on oysters is questionable, and so is the role of oysters in reducing eutrophication.
Seeing as oysters feed on algae, it seems right to think that eutrophication would benefit them- the more food, the more oysters. However, this is not necessarily the case. Availability of food is good to an extent, but beyond that it causes harm to the ecosystem, and ceases to be beneficial to oysters. For example, eutrophication may cause algae to grow in such a form that oysters do not digest, since they only eat certain types of algae (Judy). So, if eutrophication does not benefit oysters, does it harm them? There is a thought that the occurrence of dead zones has killed off oysters, and is preventing them from growing in certain areas. One response to this is that oyster mortality was not majorly due to dead zones because a large part of the mortality occurred before dead zones existed in the Bay (Keiner, 208). Also, dead zones are mostly found in water about 20 feet or deeper, but oyster beds are located in shallower water, so present mortality is not really affected by a lack of oxygen. Additionally, it is not the presence of dead zones that prevents oyster beds from expanding into deeper waters- they could not thrive there anyway because the bottom is too muddy (Judy). Surprisingly, eutrophication has little effect on oyster populations in the Chesapeake Bay.
Still, eutrophication and the resulting poor water quality mean an unhealthy Bay, and efforts are being done to improve it. What role oysters can play in this task is debatable. As filter feeders, there is hope that oysters can help improve water quality by reducing the amount of algae in the water. For this and other reasons, effort has and is being put into increasing the number of oysters in the Bay through sanctuaries, hatchery seed, natural seeding, and aquaculture. Of course, these methods are met with varying success. Sanctuaries, which oysters cannot be harvested from, have not been proven as helpful in restoring the Bay’s oyster population, and should not be the sole focus of restoration. Hatchery seed, oyster spat produced in a hatchery, could be disease-tolerant, but still has a fairly high mortality rate in the first year after planting. Natural seed, from oysters spawning in the wild, is of course not very dependable due to varying environmental conditions and the occurrence of disease. Oysters often tend to grow better in aquaculture because they may be less affected by sediment, disease, and predation. Many people, including one scientist that we met with at Marinetics, hope that aquaculture operations increase in the future to aid in improving water quality. However, oysters as a solution to water quality only go so far, and there are many complexities that need to be considered.
There are not nearly enough oysters in the Bay to have a significant impact on improving water quality. For this to happen, the oyster population would need to be more like what it was in colonial times, when there actually were enough oysters to filter a great deal of the Bay’s water. Based on our current Bay restoration efforts, this would be an unreasonable goal. Even if aquaculture flourished, the filtering effects of those oysters would most likely not be widespread, but instead would be more localized. Algae reproduce very quickly, so after water passes through an aquaculture operation or over an oyster bed, the algae population soon rebounds. Additionally, oysters only filter water directly around them, so an oyster bed would only filter the bottom of the water column (Merrit). They might also be filtering water that has already been filtered by nearby oysters. These are just a few examples of the oysters’ limitations in improving water quality. Another complexity is that oysters are picky, and will only eat certain types of algae, which may not be the kind promoted by eutrophication. It is also necessary to keep in mind that disease or periods of unusually low salinity can hit at any time and cause high oyster mortality (Judy). For these reasons, oysters are not entirely effective or dependable at filtering excess algae out of the water. We should not expect them to do so while we continue to put nutrients into the system. Perhaps more important reasons to encourage oysters lie with ecological services promoted by the associated reef community- like mussels which also have a great filtering capacity, and support for the seafood industry.
Besides eutrophication, there are other forms of excess coming from the land into the Bay that can negatively affect oysters, such as siltation and too much fresh water. Soil on land erodes and makes its way into the water, where it can suffocate adult oysters, but what is more problematic is that it prevents oyster larvae from settling. Sediment also clouds the water column, causing problems similar to those caused by algae blooms. Oysters also cannot tolerate excessive decreases in salinity from increased fresh water flow. Anthropogenic changes in the landscape, such as adding impervious surfaces, agricultural practices, and deforestation, have altered salinity (Seidel). Along with this, people living in the watershed can be considered a harmful excess to oysters, because of the negative impacts our actions have on them. We are an excess, and we cause excess.
The decline of oysters in the Chesapeake, and especially the decline of oysters available for public harvesting, has recently prompted a shift from traditional harvesting methods to more controlled farming of oysters- aquaculture. Oysters have been important in the region’s economy for quite some time, and aquaculture could be a way to keep the industry alive. Not meant to be a means of widespread oyster restoration for the Bay, aquaculture is a way for people to make a living, and the future of it depends on its profitability. The filtering abilities of those oysters are a beneficial side effect (Judy). Farmed oysters can have some benefits over wild oysters. There are three main types of oyster aquaculture: leased bottom which may or may not be planted with seed, bottom cages, and surface floats (Webster). Oysters farmed off-bottom, in the water column, may be less susceptible to burial and predation, and grow better at the surface where they receive more water flow. Also, disease-tolerant strains of oysters can be used more effectively in aquaculture, since they are not diluted by wild, non-tolerant strains of larvae. On the other hand, on-bottom aquaculture allows watermen to use their traditional equipment.
The practice of farming oysters has been accepted in Virginia for some time now, whereas Maryland, which is not so open-minded, has only recently begun to turn towards aquaculture (Connaughton, “Oysters”). Getting into the business is not easy, since operating capital, low-interest loans, permits, and leases for start-up are hard to obtain, as well as necessary shell material. Also, some watermen are reluctant to shift away from their traditional way of life to more modern methods of oystering. Some are opposed to off-bottom aquaculture because they believe that the good Lord meant for oysters to be grown on the bottom (Simns). They also say that most of the older guys don’t want anything to do with aquaculture (Lingerman). An increase in aquaculture could cause a change in their cultural landscape, transforming them from harvesters of the wild stock to farmers on the water. However, this may be the only way for them to maintain the industry. Aquaculture could present future opportunities for oysters and people on the Bay.
Oysters are only a small part of the bigger picture, and we cannot expect to restore their population while our actions continue to harm the Bay as a whole. In The Making of a Marginal Farm, Wendell Berry wrote, “The true remedy for mistakes it to keep from making them. It is not in the piecemeal technological solutions… but in a change of cultural (and economic) values that will encourage in the whole population the necessary respect, restraint, and care” (39). Instead of trying to clean up the Bay with oysters, we need to have more respect for the Bay and change the way we treat our environment, and this should be comprised of many efforts. Then, maybe oysters would have a better chance to thrive in the Chesapeake. Berry also wrote, “The only thing we have to preserve nature with is culture” (Preserving Wilderness). It is our culture that has made the Bay what it is today, and only we can improve it. If we want to keep our traditional cultures alive, we have to be willing to do what is necessary to preserve the nature that they are based around.
There is much uncertainty involved with oysters, water quality, aquaculture, and their futures. Relationships among them are muddy and can invoke a lot of opinionated debate. Oysters are not a simple solution for poor water quality. The science behind them is often more complex than people think. Overall, oysters are a small part of the bigger picture, and many other things need to be considered. It is unknown what the future holds for oysters, the oyster industry, and surrounding culture. This may turn out to be a great time of change in many aspects. Hopefully, clarity lies ahead, and we will gain a better understanding of what is best for the Bay and for oysters, while keeping a grasp on the rich culture and way of life revolving around them. Only time will tell.
References
Berry, Wendell. “Preserving Wilderness.” Home Economics. New York: North Point, 1987. Print.
Berry, Wendell. The Making of a Marginal Farm. Cleveland, OH: Bob Baris, 1995. Print.
C. Judy, personal communication, December 6, 2011.
C. Lingerman, personal communication, October 24, 2011.
Connaughton, Martin. “Shallow Seas: Sea grass beds and oyster bar habitats.” Washington College Chesapeake Semester. Toll Science Center, Chestertown, MD. 6 September 2011. Lecture.
Connaughton, Martin. “Oysters, Crabs, Rock, & Shad.” Washington College Chesapeake Semester. Toll Science Center, Chestertown, MD. 25 November 2011. Lecture.
D. Webster, personal communication, December 5, 2011.
J. Seidel, personal communication, December 8, 2011.
Keiner, Christine. The Oyster Question: Scientists, Watermen, and the Maryland Chesapeake Bay since 1880. Athens, GA: University of Georgia, 2010. Print.
L. Simns, Personal Communication. 24 October 2011.
Meritt, D. Personal Communication. 26 September 2011.
