Last week I shared a project on the state of the Eastern oyster, which included a review of restoration efforts in the Chesapeake region and a study on the potential impact of ocean acidification on the oyster population. As I mentioned in this report, acidification has had a major impact on the West Coast oyster industry, but has not yet had much of an effect on the East Coast. It is difficult to predict how the Chesapeake Bay will be affected by acidification, given the unique estuary that the Chesapeake is. The Bay is a mix of freshwater and saltwater, and salinity and depth vary across the estuary. Although many reports on ocean acidification exist, there are very few studies that have been conducted on acidification on coastal systems.
I learned today of a professor who has been studying the issue of acidification, and its effect on species native to the Chesapeake, such as the Eastern oyster and blue crab. Justin Ries works at the Marine Science Center in Northeastern University in Boston, and has been growing oysters and blue crabs in the lab. The organisms have been raised in water with high levels of carbon dioxide, to mimic possible future conditions on the East Coast. The results don’t look so promising for the now growing Chesapeake oyster industry. (See a 2010 Earth Magazine write-up here).
However, as mentioned, there is uncertainty as to the extent acidification will affect the Chesapeake. More studies must be conducted on coastal estuaries to be able to predict future conditions. In the meantime, representatives in the state of Maryland are attempting to bring this issue up for further study, examining the effects of acidification, and possible solutions, to be included in a report by the Maryland Department of Environment next year, (Maryland House Bill 118). Hopefully other states, especially Virginia, will follow suit.
I’m sharing a project I worked on last spring on oyster restoration in the Chesapeake Bay, and the impact ocean acidification may have on the oyster industry in the coming years. Ocean acidification is caused by the uptake of carbon dioxide from the atmosphere, and affects the ability of organisms, such as oysters, to form shells. Acidification has already caused problems for oyster farmers on the West Coast, and could become an issue in our region.
In this project I examined the decline of the oyster population in the past century, looked at the current restoration effort, and researched the potential effect ocean acidification could have on the eastern oyster. I reviewed literature on the issues, including journals, articles and webpages, and then wrote a short reflection piece. Reviews, comments, questions or critiques are welcome.
Last spring I worked on a report on the impacts of oyster acidification on the Eastern Oyster (Crassostrea virginica) population in the Chesapeake Bay. To get some background information on the oyster growing process, I visited with a neighbor who harvests oysters for consumption on Antipoison Creek. I wanted to share some pictures and my understanding of the oyster farming process from that project.
Farmer Mike grows over 40,000 oysters, off of his shore and dock, and further out, in the creek and Chesapeake Bay. Mike buys oyster larvae from a nursery outside Mathews, Virginia. The nursery produces Dermo-disease resistant triploid oysters. (A good story on the creation of triploids, and their differences from diploid oysters is here: Chesapeake Quarterly).
The larvae are raised in tanks, like the empty one above. When larvae attach themselves to a hard surface, which they must do to grow, they are called spat. Many farmers use a spat-on-shell approach; spat grow on oyster shells until they form their own shell, and are large enough to be moved. (Spat are less than 0.98 inches long; it can take up to a year for oysters to reach this size).
The oysters are then moved to a net or strainer, shown above. Mike keeps the strainers in floats, suspended in the creek and attached to his dock.
As the oysters grow, they are moved to larger cages, placed on the bed of the creek, and further out in the Bay. Separating oysters into cages at this stage reduces overcrowding and competition for food. It generally takes 2.5 – 5 years for an oyster to grow to market size ( 3 inches or longer). At this time, the oysters are collected, transported, and sold to local restaurants and markets.
Other interesting facts about the oyster farming process:
- Spawning occurs from May to September- water temperature must be between 64-68 degrees F.
- Oysters become dormant in colder water temperatures; they can survive freezing temperatures, if left submerged in water
- Oyster growth is dependent on salinity, water quality, water depth, temperature, and the presence or absence of disease, predators, sedimentation, food source
- Farmers, like Mike, must frequently test water quality, including dissolved oxygen levels, and concentrations of chlorophyll, which provides nutrients for oysters
- The oyster can grow up to 8 inches long, but is usually sold for consumption at 3 inches
Further reading on the Eastern oyster: NOAA.
Raising oysters requires a great deal of care throughout the year. I found a site on cage handling and maintenance that has seasonal instructions for raising oysters, and additional info on the farming process. (Severn River Association).
I recently read an interesting article on the work of a Virginia graduate student with the oyster aquaculture industry. The Virginia oyster population has seriously declined over the last century, due to disease, overharvesting, and sedimentation. I found the article ‘Seeds of Success’ in the December 12th issue of the Rappahannock Record, where it was reprinted from the Bay Journal. I’ll share the link below.
The article discusses the efforts of a former grad student, Mike Congrove, and a Virginia waterman, Rufus Ruark Jr, to rebuild the oyster industry in Virginia. Oysters are having a bit of a rebound in the Bay due to state-sponsored reef building and the production of disease-resistant larvae. Congrove played a part in research for the disease resistant oyster- the triploid. Author Rona Kobell highlights his research and writes of his work with Ruark to build a hatchery that employed spat-on-shell growing techniques with the triploid oyster.
Congrove is currently involved in researching water quality in the Chesapeake region. He is working with Virginia Tech to determine suitable conditions for oyster growing, and how to continue oyster production when water quality declines. Although this is not mentioned in the article, water quality is likely to become the biggest challenge to Chesapeake oysters in the near future as acidifying waters associated with climate change could have a significant impact in the Bay. For this reason, I think it will be interesting to track Congrove’s work, and see what comes of his research.