The undergradtuate research project was the completion, manipulation and assessment of a population model. The stage based population model assessed the late larval and juveniles stages of the hard shell clam Mercenaria mercenaria. There were seven class sizes input into the model starting with pediveligers and ending with juveniles at specific developmental sizes: ~0.2mm(Pediveliger), ~0.2mm+ (Dissoconch I) and ~1.0mm+ (Dissoconch II). Parameters or vital rates input into the model included growth, survival and saturation state. The aim of the model was to investigate by what degree the saturation state of CaCO3 (Ωaragonite) influences the population dynamics of Mercenaria mercenaria. My project involved adding the seventh class size to the model, and changing the constant value of saturation state to a variable parameter on a diurnal cycle. Additionally, the assessment of the model output would be the focus of the research.
The model was constructed in matlab, so the learning this software was necessary for the manipulation and completion of this model. The vital rates of survival and growth were probabilities defined from lab and field experiments published in the literature. Saturation state was incorporated into these probabilities as a way to change the values according to environmental conditions. The task of parameterizing saturation state as a cyclical function meant the reworking of how model probabilities were populated. Writing the function and integrating the varying saturation states to each time step was the dominate focus of the project before analysis.
Background literature was necessary in order to establish a range of saturation state (Ω) values to input into the model. With accurate values of saturation state obtained, three different simulation trials were run to represent the diurnal variation. The simulations ranged from high (0.20 – 2.20), medium (0.54 – 1.86) and low (0.87 -1.53). The values represent amplitudes of 0.33, 0.66 and 1.0 within a diurnal cycle. By assessing the different simulation runs all with the same mean value of 1.2, the characterization of dramatic shifts could be compared amongst the three simulation runs. Assessing the degree of change this variation had on the population was the main objective for the model output.
Once the model was completed the objectives included: assessing what stage class had the highest sensitivity to changes in vital rates, evaluation of hourly mortality rates given varying diurnal cycles in saturation state, identifying specific time in days that the population reaches stable age distribution and survivors converge to ultimate size class, and compare population growth rate of large diurnal shifts or small shifts at constant undersaturation. The output of the model provided the necessary data to assess the population dynamics and answer the above objectives. Analysis of the data was completed in matlab and Microsoft excel.
Future work for this model will be to create a separate carbonate chemistry which will run in parallel with the population model. The objective of this carbonate chemistry model will be to parameterize saturation state more completely by the components that constitute what saturation state is.
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