Genetic Health of Wild and Cultured Florida Clam Stocks

So how much genetic diversity is present in hard clam hatchery stocks in Florida relative to the state’s wild populations? This was the focus of research conducted by Dr. James Austin and his doctoral student, John Hargrove, with the UF IFAS Department of Wildlife Ecology and Conservation. In order to address this question, samples were collected from six commercial clam hatcheries along with four wild populations sourced from the east coast of Florida. A standardized set of genetic markers was used to test if there were significant differences among the various sources.

Why should we care? The primary reason why these researchers were interested in this question is because populations which contain greater quantities of genetic diversity are better suited for long-term survival. Put another way, in every population there are some individuals that survive bouts of extreme temperature, some that tolerate wide fluctuations in salinity levels, and some more resistant to disease. Because these traits have a genetic basis (i.e., these characteristics are passed from parent to offspring), it is in the best interest of clam farmers to have individuals in their hatchery populations that are capable of doing well in a variety of different circumstances. After all, predicting future changes in temperature, salinity, and disease can be a tricky business.

What do the results tell us? What these researchers found was that the hatchery populations had lower levels of genetic diversity relative to their wild counterparts, but these differences were not extreme. Additionally, the genetic makeup of hatcheries was very different relative to one other, but overall was not significantly different relative to wild populations. These results indicate clams used in hatcheries show evidence of being isolated from their wild counterparts resulting in losses in genetic diversity. But the differences observed in this study are not as pronounced as seen in other aquaculture bivalve species. Nonetheless, it is recommended that hatcheries closely track the sources and numbers of broodstock used in seed production, make efforts to produce equal amounts of seed from many different families (distinct parent combinations), and rotate new, wild individuals into the spawning stock periodically. In the long term, these simple measures will help to ensure the long-term health and persistence of Florida’s hard clam aquaculture industry.

The entire research report was recently published in the August 2015 issue of the Journal of Shellfish Research and can be viewed here.

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