RELATING PHOTOSYNTHETIC PIGMENTS AND IN-VIVO OPTICAL-DENSITY SPECTRA TO IRRADIANCE FOR THE FLORIDA RED-TIDE DINOFLAGELLATE GYMNODINIUM BREVE

The lipophilic pigment content and composition and in vivo optical density (OD) spectra for batch cultures of the Florida (USA) red-tide dinoflagellate Gymnodinium breve Davis were analyzed after exposure to irradiance treatments representative of an irradiance gradient that cells might experience in a coastal water column. Decreases in total chlorophyll (chl) content (attributable to decreases in chls a, c(1)/c(2) and c(3)) and total carotenoid content (attributable to decreases in total fucoxanthin and 19'-acylofucoxanthins, and gyroxanthin-diester) coincided with exposure to increased irradiance. The relative abundances of chi pigments remained constant whereas decreases in the relative abundances of total fucoxanthin and 19'-acylofucoxanthins, and beta-psi-carotene and an increase in the relative abundance of diadinoxanthin coincided with exposure to increased irradiance. Because gyroxanthin-diester has been observed only in a limited number of toxic dinoflagellates (of which G. breve is the only warm-water taxon), was consistently quantifiable throughout various irradiance-induced physiological states, and had a distinctive elution position and absorption maxima in the chromatographic eluent, this carotenoid may serve as a 'biomarker' for G. breve within Florida coastal waters. An analysis of variance, performed on fourth-derivative plots derived from normalized OD spectra, identified portions of the OD spectra which differed among irradiance treatments. Designated wavelengths coincided with wave crests in the fourth-derivative plots representative of absorption maxima for total chi c (460 to 468, 585 to 590 nm) and total fucoxanthin and 19'-acylofucoxanthins, and diadinoxanthin (490 to 496 nm). Stepwise discriminant analysis identified a set of 6 wavelengths (403, 541, 546, 509, 673 and 663 nm) which optimally classified OD spectra for populations among irradiance treatments. This lack of correspondence between wavelengths identified by the 2 statistical techniques was not unexpected; fourth-derivative analysis identified portions of the OD spectra where differences in the sharpness of curvature (as produced by absorption maxima of component pigments) occurred among treatments whereas discriminant analysis identified portions of the spectra which could be used to classify populations among treatments and did not necessarily have to correspond to absorption maxima. Such detectable differences in the bio-optical 'signatures' of G. breve indicate that previous light history, as manifested in the pigment component, could be incorporated into future pigment-based monitoring applications to allow for the detection and/or physiological characterization of problematic taxa prior to bloom status.