Foolproof or foolhardy? Use of selected aquaculture stocks for large scale restoration of natural oyster populations

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1 Foolproof or foolhardy? Use of selected aquaculture stocks for large scale restoration of natural oyster populations Ryan B. Carnegie, Jens Carlsson, Jan F. Cordes, Eugene M. Burreson, and Kimberly S. Reece Virginia Institute of Marine Science

2 Collapse of the Chesapeake Bay Oyster Fishery Overharvesting, environmental degradation/habitat loss, and disease were key factors in fishery s collapse Appearance of Haplosporidium nelsoni (959), intensification of Perkinsus marinus activity (98 s) hastened decline, have limited recovery Chesapeake Bay Market Oyster Landings Mortality from H. nelsoni(msx) begins Year H. nelsoni P. marinus Virginia Maryland Total P. marinus(dermo) intensifies Millions of Bushels EM Burreson

3 The Promise of Disease Resistant Stocks for Aquaculture Rearing for resistance to H. nelsoni was begun in the early 96s (Haskin and Ford 979) Selected lines exhibit greater survival, reduced H. nelsoni and P. marinus loads relative to native stocks (e.g., Ragone Calvo et al. 23) Selected lines (DEBYs, XBs) in continued development (VIMS ABC) and wide aquacultural use today

4 Should Domesticated Stocks Be Used in Restoration of Natural Populations?...A solution to the disease problem in Chesapeake Bay may lie in substituting resistant races in the lower part of the Bay for the susceptible ones still breeding in low-salinity areas without seriously altering the genetic diversity and adaptations of native oysters... Jay Andrews, 984 Can large numbers of reproductively viable domesticated oysters be deployed without adversely affecting native populations? Can disease resistance be easily conferred on susceptible native populations through introgression of domesticated stocks genes? Should genetic rehabilitation be pursued as a restoration strategy?

5 Genetic Concerns Will outcrossing of domesticated stocks result in decreased performance, through disruption of coadapted gene complexes underlying the resistance? Will introgression of domesticated lines into wild populations erode local adaptation in the native stocks? Will native oyster diversity be lost, leaving populations incapable of responding, through selection, to future challenges?

6 Are Native Chesapeake Bay Oyster Stocks In Need of Genetic Rehabilitation? C. virginica restoration dogma assumes the inferiority of native stocks with respect to disease performance-- Is this justified? ) York/Mobjack monitoring of native vs. selected stocks 2) Side-by-side comparisons at four Virginia sites 3) Lynnhaven River, Virginia H. nelsoni Prevalence (%) Wild Wild controls Selected Naïve AXB4 CDBY4 ZDMO4 XDBLA4 CAMX4 Line MBC4 YLGT4 YOBOY4 ZDXB4 Chesapeake Bay Foundation

7 ) York/Mobjack Monitoring of Native vs. Selected Stocks P. marinus and H. nelsoni in York/Mobjack Samples August-November, H. nelsoni Prevalence (%) Wild Native controls Selected Naïve Chesapeake Bay Foundation

8 2) Side-by-Side Line Comparisons at Four Virginia Sites AXB4 CDBY4 ZDMO4 XDBLA4 CAMX4 MBC4 YLGT4 AXB4 YOBOY4 CDBY4 ZDXB4 ZDMO4 XDBLA4 CAMX4 MBC4 YLGT4 YOBOY4 ZDXB4 Chesapeake Bay Foundation August P. marinus H. nelsoni Line Line

9 3) Lynnhaven River, Virginia AXB4 CDBY4 ZDMO4 XDBLA4 CAMX4 MBC4 AXB4 YLGT4 CDBY4 YOBOY4 ZDMO4 ZDXB4 XDBLA4 Wild CAMX4 MBC4 YLGT4 YOBOY4 ZDXB4 Wild August-September 25 8 J Carlsson PG Ross Mean SH: 5.9 mm 88. mm P. marinus Line Line Mean SH: 5.9 mm 88. mm H. nelsoni

10 Are Native Chesapeake Bay Oyster Stocks In Need of Genetic Rehabilitation? Local adaptation? True local adaptation will require rigorous population and quantitative genetic evaluation Data support evolution of resistance to H. nelsoni (recall also S. Ford presentation, this meeting), tolerance of P. marinus at a population level Continued assumption that native Chesapeake Bay C. virginica are inferior with respect to disease performance is dubious Wreck Shoal C. virginica, James River

11 If Native Chesapeake Bay Oyster Stocks Are Not Genetically Inferior: A restoration strategy / public policy that prescribes the deliberate reduction of Chesapeake Bay oyster diversity based on the assumption of inferiority is ill-advised Preservation of genetic diversity should be preferred as an alternative strategy Hatchery-based population supplementation should utilize local broodstocks and minimize inbreeding and bottlenecks Wreck Shoal C. virginica, James River

12 More Broadly... A focus on resistance/tolerance to H. nelsoni and P. marinus is too narrow Objective should be establishment of diverse and resilient populations that will be able to respond to any future challenges (climate change, the next exotic pathogen), not simply the two parasites already in our waters Biodiversity goals should not be simply about species inventories Population-level diversity a key J Carlsson

13 Acknowledgments Rita Crockett, Susan Denny, Lauren Martin, Martin Wunderly, and Jessica Moss Lionel Degremont, Stan Allen Dan Bacot, John Vigliotta, David Rudders, Tommy Leggett Melissa Southworth, PG Ross, Alan Birch