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OYSTER RESTORATION IN CHESAPEAKE BAY: AN ASSESSMENT OF THE ECOLOGICAL RISKS OF INTRODUCING A NEW SPECIES
Elizabeth T. Methratta, C. Menzie, T. Wickwire & W. Richkus January 14, 2009
The Problem: Decline of the Native Oyster Population
Overharvesting Habitat loss Disease (MSX, Dermo)
Current Harvest ≈ 1% Hi Historical t i l Levels L l
Oyster y Restoration in Chesapeake p Bayy
Purpose and Need: Need
To restore ecological function and economic benefit
Establish oyster population that would support sustainable harvests comparable to those in 1920-1970.
Draft Programmatic Volume 1 Environmental Impact Statement for Oyster Restoration in Chesapeake Bay Including the Use of a Native and/or Nonnative Oyster
The EIS is Evaluating a Proposed Action and 8 Alternative Actions
Proposed Action: Establish a reproductive population of the Suminoe oyster Crassostrea ariakensis in Chesapeake Bay B Alternative 5: Expand Aquaculture of S il SSuminoe Sterile i oysters
Draft Programmatic Volume 1 Environmental Impact Statement for Oyster Restoration in Chesapeake Bay Including the Use of a Native and/or Nonnative Oyster
Risk Question:
What is the risk that the aquaculture of sterile non-native non native oysters will give rise to a reproductive population of non-native oysters?
Risk Question:
What is the risk that the aquaculture of sterile non-native non native oysters will give rise to a reproductive population of non-native oysters? A Reproductive Population is conservatively estimated to be: 2 reproductive Suminoe oysters co-located within ithi 1 m off eachh other. th
Making g a Sterile Oyster y
Triploid (3n) Suminoe oysters are bred through genetic crosses between tetraploid (4n) with diploid (2n) oysters Triploid Suminoe oysters are nearly all reproductively incapable. p
4n X 2n
3n “Sterile”
Overview
Estimate the number of reproductive diploid oysters that could arise from largescale aquaculture of triploids Estimate the number of reproductive diploids within an area of co-location (1m apart) at an example aquaculture location.
The Chain of Events has 4 G ti PPathways Genetic th 1. Triploid Fertility leading to 3n X 2n cross 2. Triploid Fertility leading to a 3n X 3n cross 3. Diploids arising from initial 4n X 2n cross leading to a 2n X 2n cross (Imperfect Fidelity) 4. Triploids reverting back to diploid state l di to a 2n leading 2 X 2n 2 cross (Reversion) (R i )
Hypothetical yp Aquaculture q Locations
Potential oyster aquaculture regions (% of annual production by region) W andd Rhode Rh d Rivers Ri (5%) 1 West Patuxent River (5%) 2 3 Lower Potomac River (5%) 4 Northern Neck (38%) 5 Middle Peninsula (15%) 6 Lower Peninsula (5%) 7 Southside (5%) 8 Bayside Eastern Shore (17%) 9 Nanticoke River (5%)
All calculations made for a representative t ti aquaculture lt llocation ti
Probability y Estimates
From lab and hatcheryy studies on the Suminoe oyster and related species. Most conservative estimates used to evaluate the worst case scenario.
Chain of Events for All Pathways Starting Pop Pop. of 3n oysters =714,285
Probability P b bilit off Triploids, T i l id Diploids, Di l id Or Revertants entering Pathway Number of Oysters Fecundity of Oysters Encounter cou te Oppos Opposite-Sex te Se Ga Gamete ete Produce Viable Diploid Larvae Larvae Survive Larvae Find Substrate Larvae Complete Metamorphosis Larvae Survive Post-Settlement Period # of 2n oysters =?
Chain of Events for All Pathways Starting Pop Pop. of 3n oysters =714,285
Probability P b bilit off Triploids, T i l id Diploids, Di l id Or Revertants entering Pathway Number of Oysters Fecundity of Oysters Encounter cou te Oppos Opposite-Sex te Se Ga Gamete ete Produce Viable Diploid Larvae Larvae Survive Larvae Find Substrate Larvae Complete Metamorphosis Larvae Survive Post-Settlement Period # of 2n oysters =?
Oysters y Entering g Each Pathwayy
Prob. off Entering Pa athway
1 0.8 0.6 0.4 0.2
0.001
0.001
0.012
0 Diploids entering 3nX2n
Triploids entering 3nX3n
Diploids from Diploids from Imp Fid enter Rev. entering 2n X 2n 2n X 2n
Type of Oyster
Prob. off Entering Pa athway
1 0.8 0.6 0.4 0.2
0.001
0.001
0.012
0 Diploids entering 3nX2n
Triploids entering 3nX3n
Diploids from Diploids from Imp Fid enter Rev. entering 2n X 2n 2n X 2n
Type of Oyster
Number o of Females (X1000)
Oysters y Entering g Each Pathwayy 400
300
200
100
0.357
0.357
4.286
0 Diploids entering 3nX2n
Triploids entering 3nX3n
Diploids from Diploids from Imp Fid enter Rev. entering 2n X 2n 2n X 2n
Type of Oyster
Chain of Events for All Pathways Starting Pop Pop. of 3n oysters =714,285
Probability P b bilit off Triploids, T i l id Diploids, Di l id Or Revertants entering Pathway Number of Oysters Fecundity of Oysters Encounter cou te Oppos Opposite-Sex te Se Ga Gamete ete Produce Viable Diploid Larvae Larvae Survive Larvae Find Substrate Larvae Complete Metamorphosis Larvae Survive Post-Settlement Period # of 2n oysters =?
Number of Eggs gg Produced (x10^9) ( ) Number of Eggs (X10^9)
1400 1200 1000 800 600 400 200
9.17
9.17
0
0 Diploids entering Triploids entering Diploids from Imp Diploids from Rev. 3nX2n 3nX3n Fid enter 2n X 2n entering 2n X 2n
Type of Oyster
Mann & Evans 1998 Gong et al. 1994 Guo & Allen 1994
Chain of Events for All Pathways Starting Pop Pop. of 3n oysters =714,285
Probability P b bilit off Triploids, T i l id Diploids, Di l id Or Revertants entering Pathway Number of Oysters Fecundity of Oysters Encounter cou te Oppos Opposite-Sex te Se Ga Gamete ete Produce Viable Diploid Larvae Larvae Survive Larvae Find Substrate Larvae Complete Metamorphosis Larvae Survive Post-Settlement Period # of 2n oysters =?
Encounter Opposite-Sex pp Gamete Pro ob. of Encou untering Ga amete
0.50
0.40
0.30
0.20
0.10
0.003
0.0178
2n X 2n (Imperfect Fidelity)
2n X 2n (Reversion)
0.00 3n X 2n
3n X 3n
Pathway
Mann & Evans 1994 Gong et al. 1994 Gong & Allen 1994
Chain of Events for All Pathways Starting Pop Pop. of 3n oysters =714,285
Probability P b bilit off Triploids, T i l id Diploids, Di l id Or Revertants entering Pathway Number of Oysters Fecundity of Oysters Encounter cou te Oppos Opposite-Sex te Se Ga Gamete ete Produce Viable Diploid Larvae Larvae Survive Larvae Find Substrate Larvae Complete Metamorphosis Larvae Survive Post-Settlement Period # of 2n oysters =?
Prob. o of Produc cing Viab ble Larvae e
Produce Viable Diploid p Larvae 1 0.8 0.6 0.4 0.2 0 3n X 2n
3n X 3n
Imperfect p X 2n 2n (Imp Fid) Fidelity
Pathway
Reversion 2n X 2n (Reversion) Mann & Evans 1994 Gong et al. 1994 Gong & Allen 1994
Chain of Events for All Pathways Starting Pop Pop. of 3n oysters =714,285
Probability P b bilit off Triploids, T i l id Diploids, Di l id Or Revertants entering Pathway Number of Oysters Fecundity of Oysters Encounter cou te Oppos Opposite-Sex te Se Ga Gamete ete Produce Viable Diploid Larvae Larvae Survive Larvae Find Substrate Larvae Complete Metamorphosis Larvae Survive Post-Settlement Period # of 2n oysters =?
Pro ob. that L Larvae S Survive
Larvae Survive 0.25 0.2 0.15 0.1 0.05 0.00314
0.00314
3n X 2n
3n X 3n
0 2n X 2n 2n X 2n Imperfect Reversion ((Imp p Fid)) ((Reversion)) Fidelity
Pathway
Allen pers. comm.
Chain of Events for All Pathways Starting Pop Pop. of 3n oysters =714,285
Probability P b bilit off Triploids, T i l id Diploids, Di l id Or Revertants entering Pathway
?
Number of Oysters
?
Fecundity of Oysters
?
Encounter cou te Oppos Opposite-Sex te Se Ga Gamete ete
?
Produce Viable Diploid Larvae
?
Larvae Survive
?
Larvae Find Substrate
1.0
Larvae Complete Metamorphosis
0.25
Larvae Survive Post-Settlement Period
0.07 # of 2n oysters =?
Chain of Events for All Pathways Starting Pop Pop. of 3n oysters =714,285
Probability P b bilit off Triploids, T i l id Diploids, Di l id Or Revertants entering Pathway
?
Number of Oysters
?
Fecundity of Oysters
?
Encounter cou te Oppos Opposite-Sex te Se Ga Gamete ete
?
Produce Viable Diploid Larvae
?
Larvae Survive
?
Larvae Find Substrate
1.0
Larvae Complete Metamorphosis
0.25
Larvae Survive Post-Settlement Period
0.07 # of 2n oysters =?
Chain of Events Summary y
Pathwayy
# of Diploids p
Triploid Fertility leading to 3n X 2n cross Triploid p Fertilityy leading g to a 3n X 3n cross Diploids arising from initial 4n X 2n cross Triploids reverting back to diploid state
2.2 X 10^5 1.2 X 10^6 1.0 X 10^5 0
Total Number of Diploids after 1 Generation At 1 Field Operation = 1.48 8 X 10^6 0^
Example p Location: Nanticoke River
44 Aquaculture Facilities
After 10 Years in a Tributary with 44 Field Operations… Operations = 44 field operations X 1.48 1 48 X 10^6 10 6 oysters per operation X 10 years
= 6.5 6 5 X 10 10^8 8 Diploid Oysters after 10 years in a Tributary such as the Nanticoke River with 44 Field Operations
Overview
Estimate the number of reproductive diploid oysters that could arise from largescale aquaculture of triploids Estimate the number of reproductive diploids within an area of co-location (1m apart) at an example aquaculture location.
Area of Co-location for Diploids p
1m
Area = πr2 sq meters = 3.14 sq meters
Conservative Assumptions p
All larvae stay y within the Nanticoke basin No mortality of diploids All larvae find and settle on appropriate habitat
Number of Diploids per Co-location Area
6.5 X 10^8 diploids / 8.9 X 10^6 sq m habitat = 73 diploids per sq m =229 diploids per πr2 sq meters After 10 years, 229 diploid Suminoe oysters per area off co-location l i would ld be b expected d to arise due to aquaculture of sterile forms.
6.5 X 10^8 diploids / 8.9 X 10^6 sq m habitat = 73 diploids per sq m =229 diploids per πr2 sq meters This represents a worst case scenario outcome because conservative estimates were used at each step in the chain of events.
Uncertainty y
Many uncertainties associated with each step in the chain of events Uncertainties are due to poor understanding d di off Suminoe S i oyster biology M conservative Most i estimates i used
Potential Spread p of Diploids p
Concerns have C h been b raised d by regional commissions (Delaware Estuary, Estuary Gulf States) and other regional groups about the potential spread beyond Chesapeake p Bay. y
Conclusions
There are multiple p pathways p y that could lead to the presence of diploid Suminoe oysters The pathway involving triploids X triploid crossing yields the greatest number of diploids Conservatively, after 10 years of aquaculture of sterile il SSuminoe i oysters, 229 di diploids l id per co-location l i area would be expected.
Acknowledgments g
State and Federal Agencies Academic Partners University
of Maryland Virginia Institute of Marine Science (VIMS)
Versar & Exponent staff
Elizabeth T. Methratta, C. Menzie, T. Wickwire & W. Richkus January 14, 2009
The Problem: Decline of the Native Oyster Population
Overharvesting Habitat loss Disease (MSX, Dermo)
Current Harvest ≈ 1% Hi Historical t i l Levels L l
Oyster y Restoration in Chesapeake p Bayy
Purpose and Need: Need
To restore ecological function and economic benefit
Establish oyster population that would support sustainable harvests comparable to those in 1920-1970.
Draft Programmatic Volume 1 Environmental Impact Statement for Oyster Restoration in Chesapeake Bay Including the Use of a Native and/or Nonnative Oyster
The EIS is Evaluating a Proposed Action and 8 Alternative Actions
Proposed Action: Establish a reproductive population of the Suminoe oyster Crassostrea ariakensis in Chesapeake Bay B Alternative 5: Expand Aquaculture of S il SSuminoe Sterile i oysters
Draft Programmatic Volume 1 Environmental Impact Statement for Oyster Restoration in Chesapeake Bay Including the Use of a Native and/or Nonnative Oyster
Risk Question:
What is the risk that the aquaculture of sterile non-native non native oysters will give rise to a reproductive population of non-native oysters?
Risk Question:
What is the risk that the aquaculture of sterile non-native non native oysters will give rise to a reproductive population of non-native oysters? A Reproductive Population is conservatively estimated to be: 2 reproductive Suminoe oysters co-located within ithi 1 m off eachh other. th
Making g a Sterile Oyster y
Triploid (3n) Suminoe oysters are bred through genetic crosses between tetraploid (4n) with diploid (2n) oysters Triploid Suminoe oysters are nearly all reproductively incapable. p
4n X 2n
3n “Sterile”
Overview
Estimate the number of reproductive diploid oysters that could arise from largescale aquaculture of triploids Estimate the number of reproductive diploids within an area of co-location (1m apart) at an example aquaculture location.
The Chain of Events has 4 G ti PPathways Genetic th 1. Triploid Fertility leading to 3n X 2n cross 2. Triploid Fertility leading to a 3n X 3n cross 3. Diploids arising from initial 4n X 2n cross leading to a 2n X 2n cross (Imperfect Fidelity) 4. Triploids reverting back to diploid state l di to a 2n leading 2 X 2n 2 cross (Reversion) (R i )
Hypothetical yp Aquaculture q Locations
Potential oyster aquaculture regions (% of annual production by region) W andd Rhode Rh d Rivers Ri (5%) 1 West Patuxent River (5%) 2 3 Lower Potomac River (5%) 4 Northern Neck (38%) 5 Middle Peninsula (15%) 6 Lower Peninsula (5%) 7 Southside (5%) 8 Bayside Eastern Shore (17%) 9 Nanticoke River (5%)
All calculations made for a representative t ti aquaculture lt llocation ti
Probability y Estimates
From lab and hatcheryy studies on the Suminoe oyster and related species. Most conservative estimates used to evaluate the worst case scenario.
Chain of Events for All Pathways Starting Pop Pop. of 3n oysters =714,285
Probability P b bilit off Triploids, T i l id Diploids, Di l id Or Revertants entering Pathway Number of Oysters Fecundity of Oysters Encounter cou te Oppos Opposite-Sex te Se Ga Gamete ete Produce Viable Diploid Larvae Larvae Survive Larvae Find Substrate Larvae Complete Metamorphosis Larvae Survive Post-Settlement Period # of 2n oysters =?
Chain of Events for All Pathways Starting Pop Pop. of 3n oysters =714,285
Probability P b bilit off Triploids, T i l id Diploids, Di l id Or Revertants entering Pathway Number of Oysters Fecundity of Oysters Encounter cou te Oppos Opposite-Sex te Se Ga Gamete ete Produce Viable Diploid Larvae Larvae Survive Larvae Find Substrate Larvae Complete Metamorphosis Larvae Survive Post-Settlement Period # of 2n oysters =?
Oysters y Entering g Each Pathwayy
Prob. off Entering Pa athway
1 0.8 0.6 0.4 0.2
0.001
0.001
0.012
0 Diploids entering 3nX2n
Triploids entering 3nX3n
Diploids from Diploids from Imp Fid enter Rev. entering 2n X 2n 2n X 2n
Type of Oyster
Prob. off Entering Pa athway
1 0.8 0.6 0.4 0.2
0.001
0.001
0.012
0 Diploids entering 3nX2n
Triploids entering 3nX3n
Diploids from Diploids from Imp Fid enter Rev. entering 2n X 2n 2n X 2n
Type of Oyster
Number o of Females (X1000)
Oysters y Entering g Each Pathwayy 400
300
200
100
0.357
0.357
4.286
0 Diploids entering 3nX2n
Triploids entering 3nX3n
Diploids from Diploids from Imp Fid enter Rev. entering 2n X 2n 2n X 2n
Type of Oyster
Chain of Events for All Pathways Starting Pop Pop. of 3n oysters =714,285
Probability P b bilit off Triploids, T i l id Diploids, Di l id Or Revertants entering Pathway Number of Oysters Fecundity of Oysters Encounter cou te Oppos Opposite-Sex te Se Ga Gamete ete Produce Viable Diploid Larvae Larvae Survive Larvae Find Substrate Larvae Complete Metamorphosis Larvae Survive Post-Settlement Period # of 2n oysters =?
Number of Eggs gg Produced (x10^9) ( ) Number of Eggs (X10^9)
1400 1200 1000 800 600 400 200
9.17
9.17
0
0 Diploids entering Triploids entering Diploids from Imp Diploids from Rev. 3nX2n 3nX3n Fid enter 2n X 2n entering 2n X 2n
Type of Oyster
Mann & Evans 1998 Gong et al. 1994 Guo & Allen 1994
Chain of Events for All Pathways Starting Pop Pop. of 3n oysters =714,285
Probability P b bilit off Triploids, T i l id Diploids, Di l id Or Revertants entering Pathway Number of Oysters Fecundity of Oysters Encounter cou te Oppos Opposite-Sex te Se Ga Gamete ete Produce Viable Diploid Larvae Larvae Survive Larvae Find Substrate Larvae Complete Metamorphosis Larvae Survive Post-Settlement Period # of 2n oysters =?
Encounter Opposite-Sex pp Gamete Pro ob. of Encou untering Ga amete
0.50
0.40
0.30
0.20
0.10
0.003
0.0178
2n X 2n (Imperfect Fidelity)
2n X 2n (Reversion)
0.00 3n X 2n
3n X 3n
Pathway
Mann & Evans 1994 Gong et al. 1994 Gong & Allen 1994
Chain of Events for All Pathways Starting Pop Pop. of 3n oysters =714,285
Probability P b bilit off Triploids, T i l id Diploids, Di l id Or Revertants entering Pathway Number of Oysters Fecundity of Oysters Encounter cou te Oppos Opposite-Sex te Se Ga Gamete ete Produce Viable Diploid Larvae Larvae Survive Larvae Find Substrate Larvae Complete Metamorphosis Larvae Survive Post-Settlement Period # of 2n oysters =?
Prob. o of Produc cing Viab ble Larvae e
Produce Viable Diploid p Larvae 1 0.8 0.6 0.4 0.2 0 3n X 2n
3n X 3n
Imperfect p X 2n 2n (Imp Fid) Fidelity
Pathway
Reversion 2n X 2n (Reversion) Mann & Evans 1994 Gong et al. 1994 Gong & Allen 1994
Chain of Events for All Pathways Starting Pop Pop. of 3n oysters =714,285
Probability P b bilit off Triploids, T i l id Diploids, Di l id Or Revertants entering Pathway Number of Oysters Fecundity of Oysters Encounter cou te Oppos Opposite-Sex te Se Ga Gamete ete Produce Viable Diploid Larvae Larvae Survive Larvae Find Substrate Larvae Complete Metamorphosis Larvae Survive Post-Settlement Period # of 2n oysters =?
Pro ob. that L Larvae S Survive
Larvae Survive 0.25 0.2 0.15 0.1 0.05 0.00314
0.00314
3n X 2n
3n X 3n
0 2n X 2n 2n X 2n Imperfect Reversion ((Imp p Fid)) ((Reversion)) Fidelity
Pathway
Allen pers. comm.
Chain of Events for All Pathways Starting Pop Pop. of 3n oysters =714,285
Probability P b bilit off Triploids, T i l id Diploids, Di l id Or Revertants entering Pathway
?
Number of Oysters
?
Fecundity of Oysters
?
Encounter cou te Oppos Opposite-Sex te Se Ga Gamete ete
?
Produce Viable Diploid Larvae
?
Larvae Survive
?
Larvae Find Substrate
1.0
Larvae Complete Metamorphosis
0.25
Larvae Survive Post-Settlement Period
0.07 # of 2n oysters =?
Chain of Events for All Pathways Starting Pop Pop. of 3n oysters =714,285
Probability P b bilit off Triploids, T i l id Diploids, Di l id Or Revertants entering Pathway
?
Number of Oysters
?
Fecundity of Oysters
?
Encounter cou te Oppos Opposite-Sex te Se Ga Gamete ete
?
Produce Viable Diploid Larvae
?
Larvae Survive
?
Larvae Find Substrate
1.0
Larvae Complete Metamorphosis
0.25
Larvae Survive Post-Settlement Period
0.07 # of 2n oysters =?
Chain of Events Summary y
Pathwayy
# of Diploids p
Triploid Fertility leading to 3n X 2n cross Triploid p Fertilityy leading g to a 3n X 3n cross Diploids arising from initial 4n X 2n cross Triploids reverting back to diploid state
2.2 X 10^5 1.2 X 10^6 1.0 X 10^5 0
Total Number of Diploids after 1 Generation At 1 Field Operation = 1.48 8 X 10^6 0^
Example p Location: Nanticoke River
44 Aquaculture Facilities
After 10 Years in a Tributary with 44 Field Operations… Operations = 44 field operations X 1.48 1 48 X 10^6 10 6 oysters per operation X 10 years
= 6.5 6 5 X 10 10^8 8 Diploid Oysters after 10 years in a Tributary such as the Nanticoke River with 44 Field Operations
Overview
Estimate the number of reproductive diploid oysters that could arise from largescale aquaculture of triploids Estimate the number of reproductive diploids within an area of co-location (1m apart) at an example aquaculture location.
Area of Co-location for Diploids p
1m
Area = πr2 sq meters = 3.14 sq meters
Conservative Assumptions p
All larvae stay y within the Nanticoke basin No mortality of diploids All larvae find and settle on appropriate habitat
Number of Diploids per Co-location Area
6.5 X 10^8 diploids / 8.9 X 10^6 sq m habitat = 73 diploids per sq m =229 diploids per πr2 sq meters After 10 years, 229 diploid Suminoe oysters per area off co-location l i would ld be b expected d to arise due to aquaculture of sterile forms.
6.5 X 10^8 diploids / 8.9 X 10^6 sq m habitat = 73 diploids per sq m =229 diploids per πr2 sq meters This represents a worst case scenario outcome because conservative estimates were used at each step in the chain of events.
Uncertainty y
Many uncertainties associated with each step in the chain of events Uncertainties are due to poor understanding d di off Suminoe S i oyster biology M conservative Most i estimates i used
Potential Spread p of Diploids p
Concerns have C h been b raised d by regional commissions (Delaware Estuary, Estuary Gulf States) and other regional groups about the potential spread beyond Chesapeake p Bay. y
Conclusions
There are multiple p pathways p y that could lead to the presence of diploid Suminoe oysters The pathway involving triploids X triploid crossing yields the greatest number of diploids Conservatively, after 10 years of aquaculture of sterile il SSuminoe i oysters, 229 di diploids l id per co-location l i area would be expected.
Acknowledgments g
State and Federal Agencies Academic Partners University
of Maryland Virginia Institute of Marine Science (VIMS)
Versar & Exponent staff
