Title: Genetic%20Evaluation%20of%20Recruitment%20Success%20of%20Deployed%20Domesticated%20Crassostrea%20virginica%20Oysters%20on%20a%20Man-made%20Reef%20in%20the%20Great%20Wicomico%20River,%20Virginia.
1Genetic Evaluation of Recruitment Success of
Deployed Domesticated Crassostrea virginica
Oysters on a Man-made Reef in the Great Wicomico
River, Virginia.
- J. Cordes, J. Carlsson, M. Luckenbach, S.
Furiness, and K. Reece. - Virginia Institute of Marine Science
2Background
- Decline of the Eastern oyster in the Mid-Atlantic
Bight - Severe over-fishing
- Habitat destruction
- Pollution
- Disease impacts
Dermo found in Bay
MSX found in Bay
- Restoration strategies
- in Virginia
- Harvest limits
- Reef restoration
- Oyster translocation
- Supplementation
Dermo intensifies
3Background
- Restoration through oyster augmentation in
Virginia - Both dredged adult oysters (translocation) and
hatchery-propagated local oysters
(supplementation) have been transplanted to
various parts of the Chesapeake Bay. - Early restoration efforts using these wild
transplants were initially successful but later
hampered by mortality presumably caused by Dermo
and MSX (Southworth Mann, J. Shellfish. Res.
1998). - This prompted an unconventional approach to
restoration that included the use of domesticated
oyster strains for seeding reconstructed reefs.
4Background
- Restoration through oyster augmentation in
Virginia - In 2002 the Army Corps of Engineers (ACOE) the
Chesapeake Bay Foundation (CBF) adopted the use
of domesticated, disease-selected aquaculture
oysters (the Andrews DEBYTM strain) for
deployments on natural and man-made reefs
throughout the Virginia portion of the Chesapeake
Bay. - DEBY line established and bred for disease
- resistance and rapid growth (Ragone Calvo
- et al. 2003) by Dr. Gene Burreson and Lisa Calvo
- and currently maintained by Dr. Stan Allen at the
- VIMS Aquaculture Genetics and Breeding Center
- (ABC).
- It was hoped that DEBYs would survive disease
- challenges, reproduce, and pass on disease
- resistance to wild populations through
- introgression.
VIMS Gloucester Pt. Hatchery
5Background
- Possible drawbacks to restoration using hatchery
stocks - Little data existed on long-term performance of
DEBYs in the wild. - Little data existed on the reproductive success
of DEBYs in the wild. - DEBYs were known to have reduced genetic
variability (Carlsson et al. 2006), raising
concerns regarding negative genetic impacts on
wild oysters.
6The mtDNA Experiment
2002 Experimental seeding of reefs in
Virginias Great Wicomico River using DEBY
oysters was initiated to study how this
disease-selected aquaculture line would perform
in a restoration setting.
- Considered a trap estuary w/ high larval
retention (Southworth Mann 1998). - No significant oyster populations
- thought to exist in the system.
Potomac R.
Rappahannock R.
York R.
James R.
Great Wicomico R.
7Methods
- ACOE CBF deployed 15.5 million DEBYs between
2002-2006. (gt 90 on Shell Bar Reef, adjacent to
a historical oyster bed). -
- Annual recruitment monitored
- at Shell Bar Reef using spat
- collectors from early spring to
- late fall 2002-2007.
Year DEBY Deployments Spat Sampled
2002 79,5700 1281
2003 292,060 286
2004 1,410,000 109
2005 6,071,648 889
2006 6,928,352 2721
2007 --------------- 2197
Combined 15497760 5286
Great Wicomico River
8Methods
- To determine the self-recruitment success and
genetic impact of deployed DEBYs on wild Eastern
oysters at Shell Bar Reef - Sampled newly recruited spat from the spat
collectors deployed at Shell Bar Reef . - Used mtDNA and nuclear markers to distinguish
among wild, DEBY, and wild/DEBY hybrids. - Determined the percentage of the annual spat
fall attributable to hatchery-reared oysters
transplanted into the system.
9Methods
- Distinguishing among wild, DEBY, and wild/DEBY
hybrids - Amplified two mitochondrial genes (COI and
COIII) using PCR. - Used DNA Fingerprinting (RFLP analysis) to
determine haplotypes of each spat
Individual COI COIII
Spat 1 A A
Spat 2 A B
Spat 3 B A
Spat 4 B B
Spat 5 A C
Most common haplotype in wild and DEBYS
Rare in wild, up to 45 in DEBYS
Rare in wild and DEBYS
10Results
Genetic impact of deployed DEBYs- mtDNA data
GWR Wild Baseline GWR Wild Baseline GWR Wild Baseline GWR Wild Baseline GWR Wild Baseline GWR Wild Baseline
Collection Date AA RARE BB Total Scored BB
2002 38 0 1 39 2.48
2004 35 0 0 35 0
Totals 73 0 1 74 1.33
Spat Collections 2005-2007 Spat Collections 2005-2007 Spat Collections 2005-2007 Spat Collections 2005-2007 Spat Collections 2005-2007 Spat Collections 2005-2007
Collection Date AA RARE BB Total Scored BB
2002 1259 13 9 1281 0.70
2003 282 3 1 286 0.35
2004 109 0 0 109 0
2005 857 13 19 889 2.14
2006 2633 19 52 2704 1.92
2007 2140 25 32 2197 1.45
Totals 5630 63 97 5790 1.68
11Results
Genetic impact of deployed DEBYs- mtDNA data
2002 2003 2004 2005 2006 2007
Spat w/ BB haplotype presumed DEBY and/or hybrid 0.70 0.35 0 2.14 1.92 1.45
Subtract wild baseline 1.33 1.33 1.33 1.33 1.33 1.33
Spat w/BB from DEBYs ----- ----- ----- 0.81 0.59 0.12
Adjust for percentage DEBYs w/ BB (35) ----- ----- ----- 2.31 1.69 0.34
Double to account for male contribution ----- ----- ----- 4.62 3.38 0.68
12Conclusions
- Based on the mtDNA data
- No noticeable increase in the BB haplotype was
observed between 2002-2004 some DEBY spawning
seems to have occurred in 2005-2006 but there is
no increasing trend (yet?). - High spat falls in the GWR in 2005-2007 were
largely a result of reproduction in wild
populations. - The standing stock of wild oysters in the GWR had
probably been underestimated more recent
estimates suggest around 10-15 million (R. Mann,
VIMS, pers. comm.) prior to 2002 onset of DEBY
supplementation.
13Caveats
- The PCR/RFLP mtDNA analysis has been criticized
because - The BB haplotype isnt found in all DEBYs (not
diagnostic)- we have to adjust numbers based on
relative frequencies in DEBY and wild
populations. - The BB haplotype is maternally inherited- we
dont detect the male contribution to hybrid
spat, so we have to assume 11 sex ratios and
random mating to adjust. - The BB haplotype may be selected against-
therefore pure DEBY and hybrid spat carrying it
would not survive and we would not detect them in
our sampling.
14The Microsatellite Experiment
- To address these issues we reexamined the data
using eight newly developed nuclear
microsatellite loci - Bi-parentally inherited, so male and female DEBY
contribution can be directly assessed. - Presumably neutral markers not subjected to
selection. - Allows for the use of powerful discrimination
analyses based on Bayesian assignment tests to
distinguish both pure DEBY and hybrid offspring.
15Methods
- Randomly selected 100 spat from each of the 2006
and 2007 collections for testing. Also tested all
individuals from 2006 and 2007 with BB mtDNA
haplotype. - Genotyped these oysters as well as samples of
wild and hatchery oysters using eight nuclear
microsatellite loci . - Assigned individuals as wild, hatchery, or
hybrid using the program STRUCTURE.
16Results
- 2006 no spat w/o BB were DEBY, 2 were hybrid
- 2006 20 of spat with BB haplotype were
DEBY or hybrid
- 2007 no spat w/o BB were DEBY or hybrid
- 2007 no spat with BB haplotype were DEBY, 5
were hybrid
17Results
mtDNA Data
Microsatellite Data
2006 2007
Spat w/ BB haplotype presumed DEBY and/or hybrid 1.92 1.45
Wild Baseline - 1.33 - 1.33
Spat w/BB from DEBYs 0.59 0.12
Multiply by percentage DEBYs w/ BB (35) 1.69 0.34
Double to account for Male contribution 3.38 0.68
2006 2007
spat w/ BB haplotype assigned as DEBY and/or hybrid 5.00 1
spat w/o BB haplotype pure DEBY and/or hybrid 1.00 0
DEBY contribution 6.00 1.00
18Conclusions
- Results of the microsatellite experiment
consistent with mtDNA data and work by others
(Hare et al. 2006). - No apparent selection against the BB mtDNA
haplotype. - No apparent effect of differential reproductive
success between males and females.
19Dispersal Experiment
- Genetic impact of deployed DEBYs on neighboring
reefs - In 2007 sub-market (25-75 mm) and
- market (76-110 mm) sized oysters
- were sampled from late Spring to
- early Fall from five sites in the GWR
- during disease monitoring studies
- conducted by Ryan Carnegie.
- Oysters from each site, as well as
- samples of wild and hatchery
- oysters , were genotyped using
- four microsatellite loci.
- Oysters were assigned as wild,
- hatchery, or hybrid using the
- program STRUCTURE.
20Results
Genetic impact of deployed DEBYs on neighboring
reefs
- No hybrids found on any of the other sites
21General Conclusions
- Both mtDNA and nuclear microsatellite data
suggest some small amount of DEBY spawning and
self-recruitment to Shell Bar Reef occurred in
2005-2007, but there was no obvious increasing
trend (yet?). - High spat falls in the GWR in 2005-2007 were
largely a result of reproduction in wild
populations standing stock of wild oysters in
the GWR were probably underestimated. - Deployed DEBY oysters are surviving to market
size in the system. - Preliminary data show no evidence of DEBY
recruitment to other sites in the system. - The lack of DEBY impact in the GWR- too early to
tell? Looking in the wrong place?
22Acknowledgements
VIMS Elizabeth Francis Georgeta Constantin-
Reece Lab P.G. Ross- Eastern Shore Lab Mellissa
Southworth- Mann Lab Dr. Ryan Carnegie- Burreson
Lab Dr. Stan Allen- ABC CBF Tommy Leggett