Submitted to: Journal of Plankton Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/17/2001
Publication Date: N/A
Interpretive Summary: The Florida red-tide algae forms large explosive growths (blooms) in the coastal waters of the Southeastern United States and throughout the Gulf of Mexico; it is responsible for significant, negative impacts on public health, fisheries and tourism due to the release of a class of poisons that affect the nervous system (neurotoxins) known as "brevetoxins". The red-tide algae swims towards light and away from gravity. Thus, blooms of this organism often congregate near the water's surface, and are exposed to high levels of visible and ultraviolet (UV) radiation. This research investigated the photosynthetic and physiological responses of cultures of red-tide algae to low, medium and high levels of natural sunlight, with and without UV radiation. Results suggest that the algae has a relatively robust photosynthetic capability across a variety of visible light intensities, and has an apparent high level of resistance to UV radiation. This research should benefit 1) scientists interested in algal-related water quality issues, harmful-algal-blooms (HAB), and 2) crop-scientists interested in photosynthesis and high-light effects.
Technical Abstract: Little is known concerning the mechanisms by which microalgae, particularly bloom-forming taxa, tolerate large and variable amounts of photosynthetically available radiation (400-700 nm) and ultraviolet radiation (295-400 nm). Because Gymnodinium breve Davis often accumulates at or near the water's surface, the physiological responses of this red-tide dinoflagellate were investigated. Laboratory cultures of G. breve were incubated outdoors, and allowed to acclimate to attenuated natural irradiance. Aliquots of these cultures were incubated within Sarasota Bay, Florida, exposed to PAR+UV or PAR-only irradiances, and assessed for a variety of in vivo and in vitro responses. The three experimental days varied from overcast to sunny conditions. The maximum quantum yields exhibited midday depressions (roughly) symmetric about solar noon on the overcast and partly cloudy days, but exhibited an hysteresis on the sunny day. The induction and relaxation of the xanthophyll cycle resulted in stoichiometrically inverse accumulation of the pigments, diadinoxanthin and diatoxanthin. Only minor adjustments in chlorophyll a and fucoxanthin concentrations occurred during any photoperiod. No differences in the epoxidation state of the xanthophyll cycle pigments or in the maximum quantum yields occurred between cultures exposed to PAR-only or PAR+UV treatments. Observed differences in the oxygen production rates and other biochemical parameters between cultures exposed to PAR-only or PAR+UV treatments were not directly attributable to UV-induced effects. These findings indicate that G. breve possesses an inherent UV resistance and a robust photosynthetic capability, thereby allowing cells to acclimate to variable irradiance regimes.