Long-term Study Shows Oysters Developing Disease Resistance
A unique, 50-year data set collected by researchers at the Virginia Institute of Marine Science shows that Chesapeake Bay oysters are developing resistance to the pair of diseases—MSX and Dermo—that have helped push populations of these iconic shellfish to one percent of historical levels.
MSX disease results from an infection by the single-celled protozoan Haplosporidium nelsoni. Dermo is caused by the parasite Perkinsus marinus.
Researchers in VIMS' Shellfish Pathology Laboratory began gathering the data in 1960 as part of their "Spring Imports" project. Each May, the researchers collect about 700 oysters from a disease-free area in the Bay. The current collection site is in the upper reaches of the Rappahannock River near Ross Rock, where low-salinity waters inhibit the parasites that cause MSX and Dermo disease.
The researchers then transport these disease-free oysters to the saltier waters of the York River near VIMS, where they are placed in cages and monitored each month through October for signs of disease.
Ryan Carnegie, an Associate Research Scientist in the Shellfish Pathology Lab, says "These oysters are completely naïve, having undergone no selection for resistance to disease. The prevalence of parasites in their tissues at the end of the summer thus tells us how much MSX and Dermo is really out there in the Bay."
Results of the monitoring program show an upward trend in the prevalence of both diseases among the transplanted oysters. Infection rates for MSX have risen from 35-40% in the early 1960s to 80-90% since 2000.
Professor Eugene Burreson, who heads the Shellfish Pathology Lab at VIMS, says "our monitoring program shows that disease pressure is really high and increasing."
Despite this pressure the oysters seem to be responding. "The Wreck Shoal study in the lower James provides the most complete long-term study of disease prevalence on a wild oyster reef," says Burreson. "It clearly shows increased resistance to MSX in response to increased disease pressure." The prevalence of MSX among Wreck Shoal oysters has fallen from a high of 82% in 1996 to under 50% during recent years, and serious infections have become rare.
The Fall Survey of Dermo disease in Virginia oyster populations tells a similar story. Although the impact of Dermo among wild Chesapeake Bay oysters is still significant, it is much lower than that seen in the "naïve" spring imports in the York.
Carnegie says "decreased disease in the wild despite favorable conditions for the parasites is a clear sign of increasing resistance among our native oysters due to long-term exposure."
The data also show occasional sharp drops in infection rates during wet years, when freshwater runoff lowers the Bay's salinity. The parasites that cause MSX and Dermo prefer salinities above about 10 parts per thousand (ppt). Salinity in the brackish waters of Chesapeake Bay can range from 5-30 ppt depending on rainfall, tides, and other factors. The salinity of seawater is around 35 ppt.
There is an interesting presentation on this topic on slide share. I have pasted in the presentation below.
Disease Research - Oysters
View more presentations from sr320
Through a Shellfish Message Board we learned of this nice write up on Ocean Acidification by Nancy Shrodes click on this link to get the whole article.
What is ocean acidification (OA), and how does it happen?
Oceans act as a sink for carbon dioxide, absorbing 30% of the CO2 released into the atmosphere from burning fossil fuels. Through a series of chemical reactions an overabundance of CO2 can result in a lower pH, creating a more acidic oceanic environment (the lower the pH of a substance, the more acidic it is). In the last century alone, pH has already decreased by 0.1 units, a notable change in acidity. It is no coincidence that the onset of such rapid changes became visible after the Industrial Revolution, considering it initiated the monumental increase in greenhouse gas emissions that continues today.
While changes in temperature and pH occur simultaneously as the result of the increased release of fossil fuels, it is important to keep in mind that they are separate processes. The Intergovernmental Panel on Climate Change IPCC predicts a 0.3-0.5 unit drop in pH if current emission rates continue. These are huge changes for sensitive marine communities, occurring at faster rates than have ever occurred in the last 55 million years.
OA causes shell degradation and inhibits many species ability to calcify.
OA is a relatively new area of study, and the research that has been done thus far has identified varied species-specific responses to increasing acidification that influence reproduction, growth, and behavior. The process of OA reduces the amount of calcium carbonate available for calcifying organisms like plankton, shellfish, and corals, which use calcium carbonate to build their hard parts. Hence, OA directly inhibits their ability to create and maintain protective shells and skeletons. In studies that looked at the development of marine organisms in conditions of warmer and more acidic waters like those predicted for the year 2100, many showed thinner, weaker, and deformed shells in organisms such as mussels, clams, oysters, and scallops.
Reading this one can only wonder what the affect could be locally of having large amounts of oyster shell present in an area. It is a known buffer for acidity and thus the restoration of extensive oyster populations may be a partial offset.
Make $1750 Eating Oysters
Through delish.com we learned that the New Orleans Oyster Festival has an oyster eating contest. Bring your appetite. At last year’s tournament, Sonya Thomas sucked down 37 dozen oysters, that’s 444 in the eight minutes allotted.
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