Diurnal variation in the corrosiveness
of sediments and its effects on a hard
shell clam
Cale Miller
Dept. Fisheries and Wildlife Sciences, Oregon State
University
Dr. George Waldbusser
College of Earth, Ocean, and Atmospheric Sciences,
Oregon State University
Mercenaria mercenaria, the hard shell clam
• Marine bivalve that builds a calcium carbonate (CaCO3) shell
• The pediveliger stage (late larval) is an active feeding swimmer
• Metamorphose to juvenile stage finds habitat in the upper sediment layer
• Upon settlement a new layer of shell growth and intensive organ development
occur
• Effective shell building dependent on non-corrosive sediment conditions
~0.2mm Pediveliger
(larval)
~0.2mm+ Dissoconch I
(juvenile)
~1.0mm+ Dissoconch II
(juvenile)
Saturation state and diurnal variability
• Upper sediment layer is rich in organic matter (OM)
• Decomposition of OM leads to increased CO2 production at sediment-water
interface
• Increase CO2 decreases CO32- concentration
• Saturation state of CaCO3 is a measure of corrosive conditions (<1)
Diurnal variation in saturation state
Saturation state
2.5
2
1.5
1.2
1
0.5
0
1
3
5
7
9
11
13
Hours
15
17
19
21
23
Population model and associated
parameters
• A population model predicts a future population based on parameters
set into the model
• Model Parameters: growth (Gx), survival (Px) and saturation state (Ω)
• A low saturation state can inhibit shell formation and decrease survival
and growth
P1
Ped
G1
Ped =pediveliger
0.2mm
G2
0.4mm
G3
0.6mm
G4
0.8mm
G5
1.0mm
G6
2.0mm
Size(mm)
P2
P3
P4
P5
P6
P7
Varying degrees of saturation state:
Model simulations
• Model runs for 60 days at an
hourly time step
Ω = 0.87 – 1.53
n = ~34
• Daily variation in saturation
state, changing hourly
Ω = 0.54 – 1.86
n = ~28
• 3 model simulations low,
medium and high variability
in Ω at same mean value
• Starting population 100
• Final population size (n)
Ω = 0.20 – 2.20
n = ~19
Conclusions and future work
• Smaller class sizes are more susceptible to decreased saturation
states
• Larger daily variation in saturation state results in a decreased
population growth rate
• Higher mortality occurs with larger variations in saturation state
• Predation and settlement component will be added to the model
• A separate carbonate chemistry model will run in parallel with
population model
Acknowledgments
George Waldbusser constructed original model and served as
mentor/undergraduate advisor for project
Shan & Lynette De Silva and Robert Duncan, IDES PI’s
and program directors
Eduardo Guerrero, IDES program coordinator
Funding provided by NSF