Are Humans Creating a Decline in Oyster Populations?

Author: Logan Ou, Edited By: Emilyann Ashford

Figure 1. The above image displays several Oysters. Oysters are considered a delicacy and are sought after around the world. In the image you can see what their shells look like. Their shells are their primary defense from predators.

What are Oysters:

Oysters are bivalve invertebrates that inhabit ocean waters all over the world (1). They are filter feeders and thus are extremely proficient at creating clean water (1). These marine invertebrates have a large economic value due to their international and commercial consumption. Oysters are even farmed as part of aquaculture (1). 

Importance of Oysters:

Oysters are highly important invertebrates to the marine ecosystem. They occupy many different niches including building reefs and filtering water (3). Not only are these organisms important to their respective ecosystems, but they are also important to human agriculture. Roughly 3.5x106 tons of Pacific Oysters, Crassostrea gigas, were harvested in 2014 in the United States (3). If oysters are lost from their ecosystems there could be a bottom-up effect on the entire ecosystem. This is because oysters are a food source for many organisms and filter the water they inhabit. If the oysters are lost, then water quality will become poor and multiple organisms will lose food. Loss of oysters will also affect multiple fishery economies around the world.

Figure 2: The above image depicts how human activity can increase the acidity of the ocean. As the image says, the acidic ocean water is especially harmful to marine organisms that possess exoskeletons or shells. When excessive amounts of carbon dioxide enter the waters of the ocean, acid can be formed in the ocean.

Anthropogenic Stressors on Oysters:

There are several anthropogenic stressors that affect oyster populations. These stressors include rising ocean temperatures, ocean acidification, and chemical contamination (3). There are also several pathogens such as V. aestuarianus and V. splendidus that cause death in oyster populations (3). The increasing temperature of the ocean is also increasing the development of these pathogens (3). With more pathogens present, the mortality rate of the oysters will be higher. Ocean acidification is also extremely harmful to oysters. Carbon emissions are increasing carbon dioxide levels in the atmosphere which can create carbonic acid in the ocean. The carbonic acid can eat away at the shells of the oysters and make their shells thinner; this will weaken their defense against predators. One study using different levels of pH found that oysters lost shell mass even with non-corrosive pH levels, such as 7.9 (4). This means that oyster’s shells are extremely sensitive to pH. Other anthropogenic stressors include overfishing and habitat destruction (3).

Economic Effects of Oyster Loss:

One observational study in the Chesapeake Bay found that oyster production has declined since 2006 (2). The study suggests that roughly 4.9 million bushels of oysters were harvested annually in the Chesapeake Bay area between 2002 and 2006 (2). However, the models of this study have predicted a decline in oyster production and projects that 3.2 million bushels would be harvested in the coming years (2).  This would result in an increased price and demand for oysters and could hurt the seafood economy.

Figure 3. The above image shows conservation efforts to restore the oceans. A scientist can be seen studying the area in the image. They are the types of scientist that are helping the marine ecosystem recover.

How to save the Oysters:

Although the oysters are declining due to anthropogenic stresses, they can still be helped through conservation efforts. Donating to cleaning up our oceans and reducing carbon emissions can help the oysters recover. Reducing carbon emissions will slow the temperature and acidity increase of the ocean. If you would like to donate to creating a healthier ocean, please visit Ocean Conservancy.

Works Cited:

1. Guo, X., Wang, Y., Wang, L., & Lee, J. H. (2008). Oysters. In Genome mapping and genomics in fishes and aquatic animals (pp. 163-175). Springer, Berlin, Heidelberg.

2. Rothschild, B. J., Ault, J. S., Goulletquer, P., & Héral, M. (1994). Decline of the Chesapeake Bay oyster population: a century of habitat destruction and overfishing. Marine Ecology Progress Series, 29-39.

3. Thomas, Y., Cassou, C., Gernez, P., & Pouvreau, S. (2018). Oysters as sentinels of climate variability and climate change in coastal ecosystems. Environmental Research Letters, 13(10), 104009.

4. Waldbusser, G. G., Steenson, R. A., & Green, M. A. (2011). Oyster shell dissolution rates in estuarine waters: effects of pH and shell legacy. Journal of Shellfish Research, 30(3), 659-669.