Aggregation Dynamics of Antarctic Krill, Euphausia Superba Dana

NSF Org                 OPP
Latest Amendment Date   September 1, 1995
Award Number            9523748
Award Instr.            Continuing Grant
Prgm Manager            Polly A. Penhale
                        OPP OFFICE OF POLAR PROGRAMS
                        O/D OFFICE OF THE DIRECTOR
Start Date              November 1, 1995
Expires                 October 31, 1997 (Estimated)
Expected Total Amt.     $148,061 (Estimated)
Investigator            Mark E Huntley
                        Meng Zhou
Sponsor                 U of Cal SD Scripps Inst
                        La Jolla, CA 92093 
NSF Program             5111 ANTARCTIC BIOLOGY & MEDICINE
Fld Science             43 Biological Oceanography
Fld Applictn            0204000 Oceanography
                        0311000 Polar Programs-Related


9523748 Huntley Patchiness of zooplankton and micronekton is a feature of central importance in marine ecosystems. In the Southern Ocean, aggregations of krill (Euphausia superba) are of particular interest. The distribution and dynamics of such aggregations are critical to determining the transformation of organic matter (e.g. carbon flux) and the fate of populations in the sea. These phenomena are especially important in the mesoscale and sub- mesoscale domains, where patchiness is most strongly expressed. If the means to predict patch dynamics is lacking, then so is the means to adequately predict carbon flux and population dynamics at these scales. Traditional models of zooplankton patch dynamics generally treat animals as Lagrangian particles whose aggregations are determined solely by processes of advection and diffusion. This approach ignores behavior induced by biotic and abiotic forces and manifested as purposeful motion - motion that clearly is not governed by advection and diffusion. Attempts to acknowledge behavior in models of plankton motility have been successful at the level of the individual animal, but even the most powerful computers cannot run individual-based models to predict aggregation dynamics of n individuals. This proposal takes a new approach to modeling aggregation dynamics, based on "bio-continuum" theory, and provides for model verification against benchmark field data. Rather than relying on traditional advection-diffusion equations, which ignore behavior, the bio-continuum theory recognizes behavioral forces in the context of statistical mechanics. Model output provides information on animal behaviors, manifest as swimming velocities, that are absent from other models of patch dynamics. All key model variables are measurable using common sampling techniques, such as acoustic Doppler and multiple net systems. The proposed research consists of studying both the internal and external forces that act on aggregations of Euphausia superba. First, the internal forces of autocoherence (that act between animals to maintain patch integrity) will be measured in krill aggregations observed in the Gerlache Strait region in 1992. Our database consists of more than 20 such aggregations observed by ADCP and MOCNESS. Second, the effect of external physical forcing on krill aggregations will be studied by embedding krill swarms of typical scales in numerically modeled flow regimes that are typical of the Gerlache Strait region (Zhou and Niiler 1995), by combining the Princeton circulation model (e.g. Blumberg and Mellor 1987) with our aggregation model. This research provides a novel, dynamic theory of animal aggregations in the sea. A study of the fundamental theory, coupled with model realizations that can be compared to observed aggregations of Euphausia superba, may lead to more realistic predictions of krill patch dynamics in the Southern Ocean. Such predictions are critical to more accurate measurements of carbon flux and the population dynamics of krill.