Meeting Abstract

8.7  Sunday, Jan. 4  Predicting bloom-formation from cell-level swimming, stability & gyrotaxis in a marine alga. NISHIZAKI, MT*; GRUNBAUM, D; CATTOLICO, RA; University of Washington; University of Washington; University of Washington mikenish@u.washington.edu

Heterosigma akashiwo is an actively motile marine alga that forms localized, dense aggregations known as harmful algal blooms (HABs). Heterosigma HABs have significant ecological and economic consequences in the marine environment and their formation is variable in both time and space. These HABs are often characterized by rapid increases in cell density in the surface layer of the ocean that cannot be accounted for by changes in population growth alone. An alternative explanation is that previously-dispersed cells become rapidly concentrated through swimming behavior and/or passive physical transport. A current challenge is predicting spatial distributions of these algae in realistic, moving flow environments. Because cells interact biomechanically and behaviorally with ambient flows, algal distributions cannot be predicted by simple addition of still-water swimming and flow. To measure swimming-flow interactions, we used a computerized video-based particle tracking system that quantifies the location and swimming orientation of large numbers of individual cells with high levels of spatial and temporal resolution. Still-water observations were made of cells (diameter ~ 10 microns) swimming freely within a stably-stratified 1.5 L tank. Observations were also made of cells swimming in a cylindrical tank in pure vorticity (solid-body rotation around its horizontal axis). Reconstructed cell trajectories from these experiments provided parameters for a turbulence model predicting the spatial distribution of cells during HAB formation in an estuary environment.