Collaborative Research: Advection and Population Dynamics of Calanus Finmarchicus in Mesoscale Eddies in the Barents Sea: A Quantitative Approach Using the Biomass-Spectra Model

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9908079/9906757Ashijan/ZhouThe Barents Sea contains a fishery rich in commercially important species such as capelin, polar cod, and herring. The southern Barents Sea functions as a critical nursery area for the herring, which depend on zooplankton stocks during early life stages, and also supports populations of the planktivorous polar cod and capelin. It has been suggested that Calanus finmarchicus, as an expatriate in Arctic waters, may not reproduce successfully or be capable of sustaining its populations. The transport of zooplankton into the southern Barents Sea by the Norwegian Atlantic Current (NAC) and the Norwegian Coastal Current is an important mechanism to the Barents Sea ecosystem. To understand the spatiotemporal distribution and fate of zooplankton in the ocean, it is necessary to understand the interaction between advection, migration behavior, and population dynamics, especially at the mesoscale. This interaction is most profound in polar regions because the internal Rossby Radius is on the order of 101 km. Obtaining quantitative measurements of 3-dimensional advection and in situ population dynamics rates of plankton in a mesoscale eddy are daunting tasks. Traditional sampling and experimental methods cannot resolve processes at mesoscales. Acoustic instruments can resolve these scales, but cannot provide information necessary for traditional models to estimate population dynamics rates. Optical instruments, such as the Optical Plankton Counter (OPC) or Video Plankton Recorder (VPR), can provide information on the size-distribution of zooplankton at high vertical and temporal resolution but have not been used for the study of zooplankton rate processes. Theories and models describing rate processes in zooplankton based on size structure exist but have not been applied extensively.The PI's of this project have synthesized survey strategies using new high-resolution sampling methods with new mathematical theories of population dynamics and objective analysis, yielding a quantitative approach to the study of advection, vertical migration, and population dynamics of zooplankton on unprecedented scales. This project will undertake a critical test of this synthesis of theories and survey strategies in Tromsoflaket, northern Norway. Tromsoflaket is an important ecosystem located where the Norwegian Atlantic Current (NAC) bifurcates. A permanent eddy is formed in Tromsoflaket between these two branches. The northeast-flowing branch of the NAC appears to be an important mechanism for transporting zooplankton productive shelf water farther northwards into the Barents Sea during the productive season. In the vicinity of Tromsoflaket, a single species (Calanus finmarchicus) accounts for 95% of the copepod biomass in May and June. A composition of mixed species is found in August and September. This provides opportunities to test our new approach first in a simple case of a single dominant species, and then in a more complicated general case of mixed species.The successful outcome of this research could lead to an understanding of how zooplankton population dynamics in mesoscale eddy systems support high trophic levels in Arctic regions, and represent an important advance in biological oceanography, opening up the possibility of high-resolution measurements of zooplankton dynamics in mesoscale eddies, not just distributions.