Linked Biophysical Modeling

## Linked Biophysical Modeling in the California Current System: The Influence of Circulation and Behavior on Prominent Mesozooplankton Species

T. Powell [Univ. of California, Berkeley] and D. Haidvogel [Rutgers Univ.]

Eastern Boundary Current Systems, such as the California Current System (CCS), owe their high phytoplankton productivities to circulation patterns that bring nutrient-rich deep waters to the surface. Further, the spatial patterns of high primary and secondary productivity appear to be closely linked to mesoscale physical structures (e.g. filaments, jets, and eddies) in the CCS. We hypothesize that both spatial distribution and demographic processes (e.g. growth, fecundity, mortality) of calanoid copepods (e.g. Calanus pacificus and Metridia pacifica) and euphausiids (e.g. Euphausia pacifica), are influenced by circulation patterns within the CCS. We also hypothesize that the vertical migration behavior of these zooplankton influences their spatial distribution and demographic processes through the interaction between vertical migration and the circulation field. Moreover, the bioenergetic and behavioral differences between species are hypothesized to influence differential population successes and spatial distributions.

To address these hypotheses, we will construct a series of linked physical-biological models of the CCS. We propose to use an individual-based bioenergetics model to simulate CCS zooplankton behavior and phenology, to simulate the CCS circulation field with SPEM5. 1, and to link the two via simulated Lagrangian drifters.

Using the linked models we intend to address the following questions:

- How does the circulation field (e.g., upwelling, rapid offshore transport in filaments) impact the distribution and population success of major CCS zooplankton species such as Calanus pacificus, Metridia pacifica and Euphausia pacifica?

- How does the behavior (e.g., vertical migration) of these species interact with the circulation field ? How does this interaction influence the distribution and population success of these species?

- How do bioenergetic differences (e.g., in growth effficiency) and behavioral differences (e.g. in vertical migration excursion) affect the relative distribution and population success of C. pacificus, M. pacifica and E. pacifica?

In general, the models developed in this project represent a major advance in incorporating detailed zooplankton biology and ecology into realistic, three-dimensional circulation models. The method we have chosen, coupling a bioenergetics individual-based model, that includes behavior, with a detailed physical circulation model is generally applicable to populations in other ocean ecosystems.

The results of this proposal will:

- improve our understanding of how diel vertical migration and circulation interact to affect the spatial distribution and population success of important CCS zooplankton species.

- explore how three dominant CCS mesozooplankters, C. pacificus, M. pacifica, and E. pacifica respond differentially to the physically and biologically complex environment of the CCS. This is of particular interest because, although the two copepods are similar in size, they have distinct behavioral differences that should impact both their spatial distribution and population success in the CCS. Conversely, the contrast of the euphausiid with the two copepods will provide insights on how relative differences in both bioenergetics and behavior impact spatial distribution and population success.