Zooplankton distribution, transport and population dynamics in the California Current off Oregon during the 2002 upwelling season

The coastal upwelling region off the Oregon coast has been long recognized as a high production area, though it is not clear how currents transport and redistribute the production. High temporal and spatial resolution surveys with coupled hydrographic and zooplankton measurements provided the basis of a quantitative estimate of zooplankton biomass advection and retention in the upwelling region. This research revealed that zooplankton cross-shelf transport is highly associated with mesoscale features which are induced from the flow-topographic interaction. The offshore meandering also transports tremendous zooplankton biomass from the north of Newport, OR and the south of Crescent city, CA, and retains the production in the coastal region. A long residence time area of biomass on Heceta Bank, a submarine bank off central Oregon, was identified with a residence timescale of over 15 days estimated by the total zooplankton biomass and the transport of the biomass gradient. The biomass spectra constructed within this long residence time area from sequential surveys 7 days apart demonstrated a biomass propagation from small sizes to large sizes. The zooplankton in situ size-dependent growth and mortality rates were calculated using inverse methods. The potential production and the biomass recycling of zooplankton community were also examined.;This study is the first approach towards a quantitative estimate of zooplankton biomass advection and retention processes associated with mesoscale features, and the comparison of biomass changes due to biomass advection the growth processes. This work will lead us to a broader understanding of the interaction of physical and biological processes, ecosystem structure, and its carry capacity in an upwelling system.