determine for a population vertically dispersed in a stratified water column.
(^) Despite the difficulties, there are well-worked examples. Li et al. (2006) combined
a model of the circling water flow (anticyclonic, driven by tidal rectification) over
Georges Bank with a model of the progress of the advected C. finmarchicus
population through its generation cycles. They attempted to estimate not only birth
and stage-by-stage mortality, but also the entrainment of stock over, and dispersive
losses from, the bank. Stage durations, strongly affected by seasonal temperature
variation, were accounted for based on a laboratory rearing study by Campbell et al.
(2001). Li et al. included some slowing of development from food limitation by using
an averaged time-series of chlorophyll data. A model copepod stock was dispersed
into a model of the average hydrodynamics, and its mortality rates were estimated by
so-called data assimilation (the “adjoint method”) of a climatology (an average spatial
and temporal pattern) of stage abundances developed from the GLOBEC Georges
Bank sampling program. The mathematics of such modeling are complex and are
rarely fully presented in papers applying them, so we leap here to the conclusions.
Additions to stock were primarily from on-bank reproduction (Fig. 8.14). Biological
sources of mortality (predation, parasitoids, ...) were strongly dominant compared to
dispersion off the bank. Mortality rates were 20–40% less than those found by the
Mullin–Brooks method, leaving room for development of an adequate number of C5
to supply the large diapause population that develops off the bank by July.
Fig. 8.14 Mortality rate (d−1) estimates for C. finmarchicus from a model combining
advection and horizontal diffusivity over Georges Bank with the developmental
population dynamics of the resident stock of that copepod. Reproduction and
mortality were tuned to fit spatially variable plankton abundance and stage
composition data. Black bars represent best estimates of mortality if some stock can
recruit from outside (based on data from outside), while gray bars represent mortality
with no recruiting. Very small increments to mortality are required to account for in-
bound advection of stock. Clearly on-bank, reproductive stock recruitment is
dominant over recruitment by advection.
(After Li et al. 2006.)