Corbicula Transplant Studies
Corbicula Transplant Studies Thomas Benzing (JMU) Doug Graber Neufeld (EMU)
Can Corbicula be used as biomonitors to identify locations of interest with respect to mercury in the South River? • Pilot Study & Seasonal Data: Doug • Plant Reach Study: Tom
Why use transplanted Corbicula? • Transplanted Corbicula could be used to monitor mercury levels at any river site, rather than only where Corbicula is currently found. • Using transplants provides increased control of exposure conditions.
Corbicula Natural History • High biomass • Filtration rate is high • Able to filter bacteria (unlike many other bivalves) • Relatively mobile • Short life span (2-3 yr) with periodic mass die-offs • Probably lower tolerance for stress than native clams • High production of “pedi-veligers” during reproduction
Transplant group of Corbicula from North River to cages at Augusta Forestry Center
Control group of Corbicula from Augusta Forestry Center moved into cages.
Monthly Sampling of cages from 11-27-03 to 8-24-04 (subsequent sampling of uncaged clams to present) • Ten clams (making 1 composite sample) from each of six cages (three control and three transplant) • Clear GI tract 48 h prior to shucking • Mass and length data collected for growth parameters
Observations on caging technique • Usually off sediments, but sometimes buried long periods without mortality in winter/spring. Higher mortality in summer. • Cages shift during high flow • Algae and/or bacteria proliferate on mesh
0.500 Control
0.400
Transplant 0.300
mean ± std error
0.200 0.100
Days since caging
1. Initial rapid uptake by transplanted clams
Jul
Aug
280
Je
252
May
224
Apr
196
Mar
168
Feb
140
Jan
112
28
0
Dec
84
0.000 56
Total Hg (ppm wet weight)
Results of monthly sampling
Control Transplant
Days since caging
Aug
280
Jul
252
Je
224
May
196
Apr
168
Mar
140
Feb
112
Jan
56
28
Dec
84
mean ± std error
0
Total Hg (ppm wet weight)
1.000 0.900 0.800 0.700 0.600 0.500 0.400 0.300 0.200 0.100 0.000
Die-Off Reproduction
2. Later fluctuations over short time periods 3. Transplanted clams never accumulated as much as controls 4. Mercury in control clams was unaffected by caging
Control
2.00
Transplant mean ± std error
1.50 1.00 0.50 0.00 Aug
280
Jul
252
Je
224
May
196
Apr
168
Mar
140
Feb
112
Jan
56
28
Dec
84
-0.50 0
Shell length change relative to start (mm)
How does growth affect mercury uptake?
Days since caging Die-Off Reproduction
1. Length increase occurs primarily in late April/early May, corresponding to the start of reproduction
control transplant
1.2
mean ± std error
0.8 0.6 0.4 0.2 Water temperature, Jackson River 280
Aug
252
Jul
224
196
168
140
Mar Days Apr Je after May transplant
112
Feb
84
Jan
56
28
Dec
0
mass in grams
1
Days since caging Die-Off Reproduction
1. Most of tissue growth occurred before reproduction 2. Tissue growth continued in coldest time of year
Do these growth events correspond to mercury changes?
Control 0.800
Transplant mean ± std error
0.600 0.400
Days since caging
Aug
Die-Off Reproduction Shell Growth
Tissue Growth
280
Jul
252
Je
224
May
196
Apr
168
Mar
140
Feb
112
Jan
56
Dec
28
0.000
84
0.200
0
Total Hg (ug) per clam
1.000
Do high water events correlate with mercury changes?
Total Hg (ug) per clam
1.000
Control 0.800
Transplant mean ± std error
0.600 0.400 0.200 0.000
Dec
Jan
Feb
Mar
Apr
May
Je
Jul
Aug
MeHg = 32.3% ± 2.7
MeHg = 57.6%, 54.6%
MeHg = 24.5% ± 6.6 Control 0.800
Transplant mean ± std error
0.600 0.400
Days since caging
Jul
Aug
280
Je
252
May
224
Apr
196
Mar
168
Feb
140
Jan
112
Dec
56
0
0.000
84
0.200
28
Total Hg (ug) per clam
1.000
Die-Off Reproduction Shell Growth
Tissue Growth
• Percent MeHg was greater in August than in March
THg (ppm wet mass)
0.600 0.500 0.400 0.300 0.200 0.100 0.000 70.0%
%MeHg
60.0% 50.0% 40.0% 30.0% 20.0% 10.0% 0.0% 0
0.5
1
1.5
2
mass (g)
• Size had little effect on mercury contents (in August)
Can transplanted Corbicula be used as a biomonitor? • Abundant • Good survival • Cages are reasonably stable • Mercury is rapidly accumulated
Suggestions: • Timing makes a difference: Optimal period is May to July? • Two months could be sufficient for uptake
Control 0.800
Transplant mean ± std error
0.600 0.400
Days since caging
Aug
280
Jul
252
Je
224
May
196
Apr
168
Mar
140
Feb
112
Jan
56
Dec
28
0.000
84
0.200
0
Total Hg (ug) per clam
1.000
Die-Off Reproduction Shell Growth
Tissue Growth
Suggestions for future work: • Monthly sampling for long-term trends • What does % MeHg tell us? • Refine rates of uptake & washout
Thanks to: DuPont Engineering Grant EMU students: • Andrew Dutcher • Andrew Foderaro • Daniel Brubaker • Cheryl Heatwole
control transplant S. River uncaged N. River uncaged
0.00011
mean ± std error
0.0001 0.00009 0.00008 0.00007 Sep
280
Aug
252
Jul
224
196
168
Mar Days Apr Je after May transplant
140
Feb
112
Jan
84
28
Dec
56
0.00006 0
condition index (g / mm3)
0.00012
Days since caging Die-Off Reproduction
“Condition index” increases into spring, decreases thereafter
Oct
Total mercury ppm wet mass
0.50 0.40 0.30 0.20 0.10 0.00 0
7
14 Days
21
28
Can Corbicula be used as biomonitors to identify locations of interest with respect to mercury in the South River? • Pilot Study & Seasonal Data: Doug • Plant Reach Study: Tom
Why use transplanted Corbicula? • Transplanted Corbicula could be used to monitor mercury levels at any river site, rather than only where Corbicula is currently found. • Using transplants provides increased control of exposure conditions.
Corbicula Natural History • High biomass • Filtration rate is high • Able to filter bacteria (unlike many other bivalves) • Relatively mobile • Short life span (2-3 yr) with periodic mass die-offs • Probably lower tolerance for stress than native clams • High production of “pedi-veligers” during reproduction
Transplant group of Corbicula from North River to cages at Augusta Forestry Center
Control group of Corbicula from Augusta Forestry Center moved into cages.
Monthly Sampling of cages from 11-27-03 to 8-24-04 (subsequent sampling of uncaged clams to present) • Ten clams (making 1 composite sample) from each of six cages (three control and three transplant) • Clear GI tract 48 h prior to shucking • Mass and length data collected for growth parameters
Observations on caging technique • Usually off sediments, but sometimes buried long periods without mortality in winter/spring. Higher mortality in summer. • Cages shift during high flow • Algae and/or bacteria proliferate on mesh
0.500 Control
0.400
Transplant 0.300
mean ± std error
0.200 0.100
Days since caging
1. Initial rapid uptake by transplanted clams
Jul
Aug
280
Je
252
May
224
Apr
196
Mar
168
Feb
140
Jan
112
28
0
Dec
84
0.000 56
Total Hg (ppm wet weight)
Results of monthly sampling
Control Transplant
Days since caging
Aug
280
Jul
252
Je
224
May
196
Apr
168
Mar
140
Feb
112
Jan
56
28
Dec
84
mean ± std error
0
Total Hg (ppm wet weight)
1.000 0.900 0.800 0.700 0.600 0.500 0.400 0.300 0.200 0.100 0.000
Die-Off Reproduction
2. Later fluctuations over short time periods 3. Transplanted clams never accumulated as much as controls 4. Mercury in control clams was unaffected by caging
Control
2.00
Transplant mean ± std error
1.50 1.00 0.50 0.00 Aug
280
Jul
252
Je
224
May
196
Apr
168
Mar
140
Feb
112
Jan
56
28
Dec
84
-0.50 0
Shell length change relative to start (mm)
How does growth affect mercury uptake?
Days since caging Die-Off Reproduction
1. Length increase occurs primarily in late April/early May, corresponding to the start of reproduction
control transplant
1.2
mean ± std error
0.8 0.6 0.4 0.2 Water temperature, Jackson River 280
Aug
252
Jul
224
196
168
140
Mar Days Apr Je after May transplant
112
Feb
84
Jan
56
28
Dec
0
mass in grams
1
Days since caging Die-Off Reproduction
1. Most of tissue growth occurred before reproduction 2. Tissue growth continued in coldest time of year
Do these growth events correspond to mercury changes?
Control 0.800
Transplant mean ± std error
0.600 0.400
Days since caging
Aug
Die-Off Reproduction Shell Growth
Tissue Growth
280
Jul
252
Je
224
May
196
Apr
168
Mar
140
Feb
112
Jan
56
Dec
28
0.000
84
0.200
0
Total Hg (ug) per clam
1.000
Do high water events correlate with mercury changes?
Total Hg (ug) per clam
1.000
Control 0.800
Transplant mean ± std error
0.600 0.400 0.200 0.000
Dec
Jan
Feb
Mar
Apr
May
Je
Jul
Aug
MeHg = 32.3% ± 2.7
MeHg = 57.6%, 54.6%
MeHg = 24.5% ± 6.6 Control 0.800
Transplant mean ± std error
0.600 0.400
Days since caging
Jul
Aug
280
Je
252
May
224
Apr
196
Mar
168
Feb
140
Jan
112
Dec
56
0
0.000
84
0.200
28
Total Hg (ug) per clam
1.000
Die-Off Reproduction Shell Growth
Tissue Growth
• Percent MeHg was greater in August than in March
THg (ppm wet mass)
0.600 0.500 0.400 0.300 0.200 0.100 0.000 70.0%
%MeHg
60.0% 50.0% 40.0% 30.0% 20.0% 10.0% 0.0% 0
0.5
1
1.5
2
mass (g)
• Size had little effect on mercury contents (in August)
Can transplanted Corbicula be used as a biomonitor? • Abundant • Good survival • Cages are reasonably stable • Mercury is rapidly accumulated
Suggestions: • Timing makes a difference: Optimal period is May to July? • Two months could be sufficient for uptake
Control 0.800
Transplant mean ± std error
0.600 0.400
Days since caging
Aug
280
Jul
252
Je
224
May
196
Apr
168
Mar
140
Feb
112
Jan
56
Dec
28
0.000
84
0.200
0
Total Hg (ug) per clam
1.000
Die-Off Reproduction Shell Growth
Tissue Growth
Suggestions for future work: • Monthly sampling for long-term trends • What does % MeHg tell us? • Refine rates of uptake & washout
Thanks to: DuPont Engineering Grant EMU students: • Andrew Dutcher • Andrew Foderaro • Daniel Brubaker • Cheryl Heatwole
control transplant S. River uncaged N. River uncaged
0.00011
mean ± std error
0.0001 0.00009 0.00008 0.00007 Sep
280
Aug
252
Jul
224
196
168
Mar Days Apr Je after May transplant
140
Feb
112
Jan
84
28
Dec
56
0.00006 0
condition index (g / mm3)
0.00012
Days since caging Die-Off Reproduction
“Condition index” increases into spring, decreases thereafter
Oct
Total mercury ppm wet mass
0.50 0.40 0.30 0.20 0.10 0.00 0
7
14 Days
21
28
