Cruises
11/1998 R/V Suncoaster Sanibel Island, FL
09/1999 R/V Pelican Panama City, FL
10/2000 R/V Pelican Panama City, FL
10/2001 R/V Suncoaster Sarasota, FL
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Biochemistry
The 09/1999 cruise off Panama City, FL provided the best biochemical data on field populations of K. brevis because consistently high K. brevis populations (<240 cells/mL) and chlorophyll a concentrations (around 10 ug/L) occurred at both 1 and 5 m depths throughout the two time series. However, the K. brevis population numbers were not correlated with the chlorophyll a concentrations (emphasizing the need for gated filtration/centrifugation between 1 and 40 um). and tended to decrease toward the end of the second time series. In general, sunlight followed a 12 hr light/12 hr dark cycle and the nitrate concentration exceeded 1 uM at both depths. Though the cell content of the different biochemical constituents varied with time, the pattern with depth was not consistent with the observations (biochemically depleted surface populations and biochemically enriched subsurface populations during the daylight hours - below) reported in the nutrient - replete laboratory mesocosm (Kamykowski et al. 1998a).
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Behavior
Swimming speed was determined from the analysis of video recordings with an Expertvision Motion Analysis System (Kamykowski et al. 1988) and geotaxis/phototaxis was determined using specially designed chambers as described in (Kamykowski et al., 1998b). On the 10/2001 cruise, development of chemotaxis techniques were initiated and profiling for nutrients in the water column and in sediment samples were undertaken.

The 10/2000 cruise off Panama City, FL provided the best vertical migration data on field populations of K. brevis because a near surface drogue was followed. The 25 m water column exhibited a complex migration pattern with an upper population migrating between the surface (aggregating through the day) and about 10 m depth (evenly distributed in the upper 10 m during the night) and a lower population migrating between the 15 m depth (evenly distributed in the lower 10 m of the water column during the day) and the bottom (aggregating through the night)(below). Swimming speed was about 1 m/h. Geotaxis was strongly negative while phototaxis was weakly positive in the afternoon. This is in general agreement with the results reported in Kamykowski et al. (1998b).
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Mesocosm
The supporting laboratory mesocosm experiment followed the protocols described in Kamykowski et al. (1998a) except the nitrate concentrations were first allowed to deplete and were then replenished during the course of the experiment. Samples, collected over several diel cycles to follow the biochemical changes in the populations at different depths of the water column as nitrate concentration changed, more closely resembled the patterns in field populations of K. brevis.
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Biophysical Model
Population distributions resulted from the application of the swimming rules to a variety of imposed nitrate distributions. In general, the distributions were strongly influenced by the locations of the nutrient sources. Note that vertical migrations occurred at all depths in response to the light cycle and that when nutrients were available both at the surface and at the bottom of the water column, the distribution of the cells resembled the patterns observed off Panama City, FL in 10/2000 (above). The carbon and nitrogen plots that complemented Figure 5 in Liu et al. (2001b) showed that the biochemical signatures of the populations tended to undergo complex changes when the nutrient sources were in transition from one water column interface to the other. Current effort: emphasizes a 3-D application with wind applied to sloping topography.
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Current work: Mesocosm
Current work includes the comparison of 10 K. brevis clones utilizing a radial photosynthetron. Studies include investigating the relationship of photosynthetic state, cell diameter (below) and swimming speed with various light and temperature combinations.
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Current Work: Mimic Study
A Lagrangian drifter (bottle-shaped object about 30 cm long and 12 cm in diameter with a 30 cm diameter drag skirt around the middle - below) will be used to mimic K. brevis in the flow field as an in situ tracer. This "Plankton Mimic" uses buoyancy changes to substitute for directionally - applied flagellar propulsion. If successful, the mimic will provide a way to follow K. brevis populations while recording information about the history of environmental exposure supporting cell growth/division and about changes in time-space coordinates in response to ambient currents. The drifter was developed by T. G. Wolcott and D. L. Wolcott at North Carolina State University.
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Last Modified: January 7, 2004