Biochemical Analysis of Diel Vertical Migration in the Red Tide Dinoflagellate Karenia brevis

Abstract

Many laboratories have solely used the Wilson isolate to characterize the red tide dinoflagellate species Karenia brevis. Recent work has provided new isolates from different geographical locations. Prior to detailed biochemical investigations, laboratory studies were conducted on ten different isolates representing geographical locations around the coast of Florida. The investigation of the physiological parameters for the ten different isolates provided a foundation for the proper selection of a single isolate that would closely represent the species in the field. Each isolate was capable of a range of responses with primary dependence on cell counts within the cultures. Evidence suggests that either carbon limitation or bacterial negative feedback caused changes in the physiological parameters as cell counts increased. The Apalachicola isolate was selected for further biochemical investigations because it was representative of the group response.

A nutrient-replete intermediate-light mesocosm experiment investigated the taxis patterns, and the biochemical composition of vertically migrating K. brevis populations. This experiment confirmed the internal biochemical status of the cell controlled migratory behavior, growth and reproduction. Young cells fixed carbon at the surface while older cells limited vertical migration toward the middle depth in anticipation of cellular division. The cells were capable of performing complex lipid control during vertical migration. Quick turnover of these lipids indicated K. brevis was more than capable of taking advantage of changing physical conditions.

Finally, nutrient replete and deplete mesocosms investigated how K. brevis responded to field-simulated high light conditions. Results from high light and nitrogen-limited exposure suggested K. brevis may utilize the benthos by minimizing exposure to oxidative stress and as a nitrogen source supplied from benthic pore-water flow in permeable sediments. High light also caused K. brevis to increase toxin concentrations while decreasing its sterol lipid class concentrations. This response caused K. brevis to be more toxic at particular times of the day. Data from this experiment led to the conclusion that cell division yielded unequal daughter cells.