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Abstracts
Workgroup: Oyster Fisheries Management and Restoration
Environmental effects on Perkinsus marinus infection rates, growth and survival among dermo-disease-free juvenile oysters planted at three salinity regimes in an enzootic Chesapeake Bay Oyster Recovery Area (continued)
Principal Investigator(s):
George Abbe, Academy of Natural Sciences Estuarine Research Center, abbe@acnatsci.org
Co-Investigator(s):
Chris Dungan and Steve Jordan, Sarbanes Cooperative Oxford Laboratory
Funding Period: Oct. 1, 2001 - Sept. 30, 2003
In 2002 specific pathogen-free (SPF) oysters were set on oyster shell and deployed along a salinity gradient in the Patuxent River, Maryland to investigate environmental effects of Perkinsus marinus on infection rates, growth and survival. Spat were deployed at the three original sites located on oyster bars and a new site at Sandgates (SG) located at least 1 km from natural bars for assay of P. marinus infections by the whole body burden technique which allowed an estimate of time to initial infection and subsequent progression of dermo disease. Additional oysters were monitored monthly for growth and mortality. Thirty oysters from the natural population at each site were also examined monthly by rectal tissue assay. During the first year, salinity at Holland Point (HP, upper river), Gatton (GAT, mid) and Town Creek (TC, lower) averaged 11.1, 13.0 and 14.4, respectively, but during the second year averaged 13.3, 15.8, and 16.9.
Spat at HP, GAT and TC grew 23, 34 and 27 mm, respectively, and survival was 95, 98 and 94% during the first year. During the second year, however, growth was slightly better at HP (21 mm) than at GAT (16mm) or TC (19mm), but mortalities began to accelerate in October 01 at TC, in June 02 at GAT and in August 02 at HP. By August 2002, mortalities at HP, GAT and TC were 60, 98 and 97%, respectively, and HP reached 97% 2 months later. Two discrete spat sets and deployments were made: May 2002 and September 2002. From the May deployment, SPF oysters placed at SG, remote from existing populations, acquired infections by day 27 (13% prevalence), as did juveniles deployed at TC (7%) and HP (3%). At all sites animals acquired P. marinus infections within 62 days, with prevalences of 10%, 63%, 43%, and 37% (TC - HP). By 91days post-deployment all sites, with the exception of TC, had infection prevalences greater than 90%, and these elevated prevalences continued through 127 days. At 91days TC prevalence remained low at 10%, but by 127 days it increased to 53%. In October prevalences declined at TC, GA, and SG (154 days), but all remained above zero into mid-November. SPF juveniles deployed in late September acquired P. marinus infections by 4 weeks at all sites, however prevalences were low and declined at 8 weeks, with infections detected then only at HP.
Mean intensity of dermo disease among feral populations (on a scale of 0-7) at HP, GAT and TC averaged 2.51, 2.72 and 2.79, respectively, during the first year and 2.65, 2.81, and 1.81 during the second. Mortalities were high on all three bars.
IMPACTS and/or BENEFITS:
Two major impacts have resulted from this study so far. (1) During times of severe drought, there are no safe areas to plant disease-free seed except the most upriver areas that can be tolerated. (2) SPF juvenile oysters placed at sites remote from natural oyster populations harboring P. marinus acquire infections at similar rates as SFP juveniles placed adjacent to natural populations. This finding could have a major impact on planting of both natural and hatchery seed, which some have thought would remain disease free if planted away from existing populations or on natural bars that had been cleaned of older infected oysters.
PROJECT PUBLICATIONS:
George R. Abbe, Brian W. Albright, Carol B. McCollough, Christopher F. Dungan and Stephen J. Jordan. 2002. Environmental effects on Perkinsus marinus infection rates, growth and survival among dermo-disease-free juvenile oysters planted at three salinity regimes in the Patuxent River, Maryland. Journal of Shellfish Research 21:371. (This was also an invited paper presented at the National Shellfisheries Association meeting in Mystic, Connecticut in April 2002.)
Carol B. McCollough, Christopher F. Dungan, Stephen J. Jordan, George R. Abbe and Brian W. Albright. 2002. Perkinsus marinus infection rates in specific-pathogen-free juvenile oysters planted at three salinity regimes in the Patuxent River, Maryland. Journal of Shellfish Research 21:375. (An invited paper presented at the National Shellfisheries Association meeting in Mystic, Connecticut in April 2002.)
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