Combined effects of light and naphthalene on marine microalgae

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In this study, I investigated the combined effects of light and naphthalene on marine microalgae. The growth of many groups of phytoplankton is strongly inhibited by combined high light irradiation(2000 μmol m^<-2> s^<-1>) and naphthalene(0.05-5 ppm) because of the combined effects of photoinhibition and toxicity. The xanthophyll cycle of microalgae is thought to protect against photoinhibition : light in excess of photosynthetic capacity is known to rapidly change xanthophyll pigments of green algae from violaxanthin via antheraxanthin to zeaxanthin, and those of diatoms from diadinoxanthin to diatoxanthin. Irradiation of microalgae at 2000 μmol m^<-2> s^<-1> during exposure to naphthalene at >15ppm caused the fastest change in xanthophyll pigments among four conditions(200 or 2000 μmol m^<-2> s^<-1> and 0 or >15 ppm naphthalene). Naphthalene decreased the production of dissolved oxygen, an indicator of photosynthesis. Therefore naphthalene inhibited photosynthesis, and rapidly activated the xanthophyll cycle. Microalgae produce mycosporine-like amino acids(MAAs), whose absorbance maxima lie in the ultraviolet(UV) region, to protect against inhibition by UV radiation. The production of dissolved oxygen was decreased by the synergistic effects of UV-A(~360 nm), high light irradiation, and naphthalene. It was not clear whether the ratio of MAAs to chlorophyll a was changed by UV-A and naphthalene. It appears that the production of MAAs in microalgae used in this experiment was not influenced by UV-A and naphthalene.