Oysters and the Chesapeake Bay

Anyone who has spent any amount of time in Baltimore, my hometown, probably knows the Chesapeake Bay, the largest estuary in North America, is not healthy. The thought of Fells Point on a humid night in July or August wouldn’t be complete without the ubiquitous smell of the harbor after a storm, when all of the trash has been washed toward shore. It’s fairly innocuous, just present if you take the time to notice. However, for a few weeks of summer 2007, the smell wasn’t just present, it was overwhelming. Massive die-offs lead to hundreds of decaying fish crowding Fells Point and the Inner Harbor, the parts of town responsible for tourist revenues, and where my sister worked at the Maryland Science Center.

The die-offs were due to a dead zone in the bay, which stretches for hundreds of miles in the summer. Dead zones are the result of depleted levels of dissolved oxygen in the water, a problem known as hypoxia. (1) The root source of hypoxia is a surplus of nutrients in the water, principally nitrogen, from sewage treatment plant effluent or agricultural runoff. Essentially, the nitrogen acts as fertilizer and encourages massive algae blooms. Algae in itself would not be a large problem, but eventually it dies, and the huge amounts of decomposing algae can eat up dissolved oxygen that fish and other organisms depend on. Excess nitrogen mostly comes from agriculture, which contributes 40% of nitrogen and 50% of phosphorous which enters the bay. The problem has been steadily increasing as forests around the bay are replaced with suburbs, urban areas, and farmland. Lack of a buffer zone means that pollution can enter the bay unfiltered. (2)

The problems of the Chesapeake Bay do not stop with the blatant and massive die-offs of fish. Oysters, in particular, have drawn a lot of attention. Once, they were central to the Maryland and Virginian economies, and were the “most valuable commercial fishery” in the Bay until the 1980s (3). Additionally, they hold a key position in the ecosystem. Oysters act as a kind of natural water filter, with an adult oyster able to filter up to 60 gallons of water per day. Once, the oyster population was such that it could filter a volume of water equal to that of the entire Chesapeake in a week, but today, they same process would take about a year. Besides filtering, oyster reefs provide habitat for hundreds of other species, such as sea trout, barnacles, hooked muscles and mud crabs (3). However, this crucial species is experiencing a significant decline; population is currently at 1% of what it was in the 1950s, which was still lower than pre-Civil War populations, mostly as a result of over-harvesting and disease. Two parasites introduced from China, MSX and Dermo, have been responsible for truly massive die-offs. (4)

How to handle the dying oyster population has been widely disputed and very controversial. The first approach involves repopulating the bay with Crassostrea virginica, the species native to the east coast. Millions of dollars have been spend to rebuild oyster beds, breed disease resistant oysters and seed the area with mature oysters bred in captivity. (5) This process has been very costly and thus far has not seen much success; some rebuilt oyster beds have seen initial success, but then died of diseases less than a year later (6). As part of this plan involves a rotation of areas to be harvested, many watermen are left frustrated because they cannot access where the oysters are. One commented, “They need to open up where the oysters are” (7). Local governments responded by opening certain areas, with the justification that oysters must be harvested for sale “to increase harvest and mitigate potential oyster losses due to disease” (8). In the words of Baltimore Sun columnist Candus Thomson, “What a crock.” The local government appears to be invested in the preservation of oysters so that they can be harvested and sold, not to preserve the ecosystem for the sake of the ecosystem. Harvesting is undermining any efforts at preserving the few remaining virginica oysters in the bay.

The alternative proposed is the introduction of a new species that lives mainly around Japan, Crassostrea ariakensis. C. ariakensis has evolved in an environment similar to the bay, and infertile sample suspended in the waters of the Chesapeake have grown well, reaching the 3 inch haverstable size in nine months, as opposed to the two years it takes C. viriginica. (9) However, I find it suspect that the measure used is “marketable size;” the motives sound less than ecologically pure. C. ariakensis would still have the advantages of filtration that the Bay so desperately needs, as well as the potential to create habitats. There are though the usual problems that accompany introducing a non-native species; there are many famous examples of non-native species becoming invasive, such as kudzu or nutria. The diseases which are currently ravaging oyster populations came from Asia originally, so C. ariakensis has evolved to be able to manage them, but there is still the issue of the oysters bringing other diseases with them. Some have also raised concerns over whether the bay is currently able to support any oyster population at all; it could potentially be so polluted that any species would die out. (10)

To me, the central issue here is why we want oysters in the Chesapeake. They are economically important, but if we are going to have a sustainable population of oysters, this cannot be our main concern. There is no easy, quick way to just insert a species into an ecosystem and have it thrive. Humans caused the problems that are now plaguing the oysters: we are the ones who harvested so much that the gene pool shrank dramatically, making the population more susceptible to disease, and then we were the ones who introduced two foreign parasites. We should not think of oysters as a Brita filter for the bay; I got the impression from some policy makers that their attitude was one of “If we have enough oysters in the bay, we don’t have to worry about how much nitrogen or mercury we’re allowing to run-off.” This is not the case. When looking at oyster populations, we cannot just look at that population. The Chesapeake Bay is an improbably assembly, just like any cell, and it is the interaction between its disparate parts that make it what it is. We cannot build a functioning cell because the interactions within it are so various and so complex. In the same way, we cannot pick and choose parts of the Bay to rebuild because each organisms and species depends on its context. We cannot hope to save oyster populations without looking at what it is about our behavior that killed off the oysters in the first place.

1) http://www.cbf.org/site/DocServer/DeadZoneFactSheet_May06.pdf?docID=5583; The Chesapeake Bay’s Dead Zone, Chesapeake Bay Foundation

2)http://www.cbf.org/site/PageServer?pagename=exp_sub_resources_factsheets_waterpollution; Water Pollution in the Chesapeake Bay, Chesapeake Bay Foundation

3) http://www.cbf.org/site/PageServer?pagename=exp_sub_resources_factsheets_oysters; Oyster Fact Sheet, Chesapeake Bay Foundation

4) http://noaa.chesapeakebay.net/dermomsx.aspx; Dermo and MSX, NOAA Chesapeake Bay Office

5) http://www.chesapeakebay.net/cop.htm; Oyster Management Plan, Chesapeake Bay Program

6) http://www.bayjournal.com/article.cfm?article=641; “Native oyster projects showing signs of promise, but is it enough?”, Chesapeake Bay Journal

7) http://www.baltimoresun.com/news/nation/bal-te.oyster25nov25,0,7975980.story; Va. oyster plan has watermen wary, Baltimore Sun

8)http://www.baltimoresun.com/sports/outdoors/balsp.thomson09dec09,0,3343790.column; Oyster restoration needs a hand, Baltimore Sun

9) http://www.chesapeakebay.net/baybio.htm; Non-Native Oysters and the Chesapeake Bay, Chesapeake Bay Program

10) http://www.bayjournal.com/article.cfm?article=2748; “It’s not a matter of which oyster, but if any could thrive in the Bay,” Chesapeake Bay Journal