Calanoid copepods are key organisms in the California Current (CC) region, consuming primary and secondary production at high rates and serving as prey for larval, juvenile, and small pelagic fish, other invertebrates and certain seabirds. A critical period in the life of several calanoid species is their overwintering period, during which they leave the unproductive surface waters in mid-summer to fall and then ascend to the surface in the springtime, usually coincident with the spring bloom. However, the physical and biological cues that both initiate and terminate the dormant phase of several key copepod species within the CC are poorly known. The goal of this research is to test the hypothesis that the dormant phase of two major calanoid species, Calanus pacificus and Calanus marshallae, are in part controlled by changes in temperature and prey abundance. This hypothesis will be tested by two means. First, the existing data on relative stage abundance and vertical distribution of the two target species for four distinct locations along the west coast of North America will be compiled and compared to observational bio-physical datasets, many of which were collected as part of the GLOBEC NEP program. Second, an Individual-Based Model (IBM) for each of the two species will be developed, based on several different conceptual models of how temperature and prey availability control the dormancy response. This model will then be forced with climatological data and compared with the analysis of the field data. Further, this model will be used to test the sensitivity of each species' population dynamics to initial conditions, interaction with the timing of the spring bloom, and expected levels of climate variability. Finally, variability in the local population abundance of these two species due to responses to local climate versus population advection due to large-scale changes in physical transport will be addressed. The results of the research will be important for understanding some of the basic processes that influence the seasonal production of a major group of plankton. This knowledge is critical for understanding the overall trophic impact of climate change on marine food webs within the CC. This research involves a postdoctoral student and the information gained from this work should prove valuable to fisheries management for small pelagics and other managed invertebrate species. The results of this research will also be served to the public through a web-based Live Access Server system, thus making it readily and broadly available.
