Trans-Atlantic Study of Calanus: Modelling Growth, reproduction and life cycle

The objective of this subtask of the Trans-Atlantic Study of Calanus (TASC)
programme is to model region specific growth and egg production patterns and
life cycles, and investigate population synchrony with circle-map modelling,
based on the laboratory, mesocosm and field results.

To understand life cycle strategy and estimate production of copepods, we must
know the common characteristics of growth and development for the individuals
of the same population and the sources of their variability. Models coupling
the physiological approach with stage structure and mortality as developed by
Carlotti & Sciandra (1989) enable the dynamics of all the developmental stages,
in variable conditions of food and temperature, to be simulated. Despite
numerous experiments on the physiological processes of copepods (ingestion,
metabolism, growth) and on cohort development, the links between growth
(biomass increase) and development (stage progression) are not fully understood
(TASC Report). The experimental work proposed in the previous two subtasks will
provide an opportunity, using the data generated, to address the outstanding
question of model calibration. Modelling will also be a synthetic tool testing
hypotheses on Calanus population dynamics resulting from the laboratory,
mesocosm and field studies. To develop a life cycle model compatible with the
computational demands of operation in tandem with a particle tracking dispersal
model, an alternative approach is also necessary. Deterministic and stochastic
models to predict the optimal seasonal time for entry and exit of diapause in
species which can only overwinter in diapause have been available for some
time. These tend to be parameter rich. Gurney et al. (1992) explored the use of
circle-map models, a method used in mechanics modelling, to investigate
population synchrony for species with seasonal diapause. The models are
parameter sparse, and function by tracking generation lines, predicting
successive spawning times in relation to the periodicity of the forcing
environmental signal - precisely the approach required to simulate reproduction
in a particle tracking system. This method has shown that for insect taxa the
size and timing of entry to diapause is critical for population persistence
under seasonally adverse conditions, whilst wide flexibility in the size and
time of diapause entry and exit is a feature allowing colonisation of a wide
latitudinal range. For example, tropical insect species which succeed in
colonising temperate environments. In C. finmarchicus the diapause stage is
relatively extended in the open ocean (3-5 months). In insects this commonly
results in high degree of population synchrony. The use of circle-map models
seems appropriate for investigate this life-cycle aspect.

Existing models will be further developed, and applied to the life history
strategy of C.finmarchicus.