BIOOPTICAL CHARACTERISTICS AND PHOTOADAPTIVE RESPONSES IN THE TOXIC AND BLOOM-FORMING DINOFLAGELLATES GYRODINIUM-AUREOLUM, GYMNODINIUM-GALATHEANUM, AND 2 STRAINS ON PROROCENTRUM-MINIMUM

Photoadaptive responses in the toxic and bloom-forming dinoflagellates Gyrodinium aureolum Hulbert, Gymnodinium galatheanum Braarud, and two strains of Prorocentrum minimum (Pavillard) Schiller were evaluated w ith respect to pigment composition, light-harvesting characteristics, carbon and nitrogen contents, and growth rates in shade- and light-ada pted cells. The two former species were grown at scalar irradiances of 30 and 170 mu mol.m(-2).s(-1) at a 12-h daylength at 20 degrees C. Th e two strains of P. minimum were grown at 35 and 500 mu mol. m(-2).s(- 1) at a 24-h daylength at 15 degrees C. For the first time, chlorophyl l (chl) Cn characteristic of several bloom-forming prymnesiophytes, wa s detected in G. aureolum and G. galatheanum. Photoadaptional status a ffected the pigment composition strongly, and the interpretation of th e variation depended on whether the pigment composition was normalized per cell, carbon, or chl a. species-specific and photoadaptional diff erences in chl a-specific absorption ((o)a(c) 400-700 nm) and chl a-no rmalized fluorscence excitation spectra of photosystem II fluorescence with or without addition of DCMU (F-o and F-o(DCMU), 400-700 nm) were evident. Gyrodinium aureolum and G. galatheanum exhibited in vivo spe ctral characteristics similar to chl c(3)-containing prymnesiophytes i n accordance with their similar pigmentation. Prorocentrum minimum had in vivo absorption and fluorescence characteristics typical for perid inin-containing dinoflagellates. species-specific differences in in vi vo absorption were also observed as a function of package effect vs. g rowth irradiance. This effect could be explained by differences in int racellular pigment content cell size/shape, and chloroplast morphology /numbers. Light- and shade-adapted cells of P. minimum contained 43 an d 17% of photoprotective carotenoids (diadino + diatoxanthin) relative to chl a, respectively. The photoprotective function of these caroten oids was clearly observed as a reduction in F-o and F-o(DCMU) at 400-5 40 nm compared to (o)a(c) in light-adapted cells of P. minimum. Spectr ally weighted light absorption (normalized to chl a and carbon, 400-70 0 nm) varied with species and growth conditions. The use of quantum-co rrected and normalized fluoreseence excitation spectra with or without DCMU-treated cells to estimate photosynthetically usable bight is dis cussed. The usefulness of in vitro absorption and fluorescence excitat ion spectra for estimation of the degradation status of chl a and the ratio of chl a to total pigments is also discussed.