Modelling copepod development: current limitations and a new realistic approach

To predict the influence of environmental variability on copepod dynamics and production, models must account for the effects of temperature and food on stage-dependent time-scales. Here, data for development-time means and variance of Colon us finmarchicus are used to quantify the limitations of existing models. Weight-based individual models are sensitive to uncertain parameters, such as moulting weights, assimilation efficiency, and environmental dependencies, making them highly difficult to calibrate. The accuracy of stage-based population models using ordinary differential equations depends on model structure, with some predicted generation times being incorrect by months. Even when large numbers of age classes are used to reduce modelled variability, it is not possible to make variability consistent with the data. Accuracy of mean times for stage-based population models using difference equations requires a small time-step, which results in large numbers of age classes and modelled variability that is underestimated by orders of magnitude, unless a probabilistic moult fraction is used. We present a new stage-based individual model that avoids the limitations of other models and successfully represents C. finmarchicus mean development timing and associated variability. This approach can be adapted easily for other species, as well as dynamic environmental conditions.