UV-B Induced Changes Of Growth And MAAs In HAB Causative Algae From South China Sea

In the present study, UV-B induced changes of growth and MAAs in 6 speciesof HAB from South China Sea was investigated. Techniques of High-performanceliquid chromatographic (HPLC) was used to dectect UV absorbing compounds in thealgae under enhanced UV-B radiation. The results provided new evidences forexplaining possible mechanism of enhanced solar UV-B radiation on red tide.UV-B radiation inhibited the growth of the 6 HAB species widely distributed inSouth China Sea. Growth inhibition increased with UV-B radiation dosage. Celldensity of Heterosigma akashiwo, Alexandrium tamarense and Skeletonema costatumshowed different sensitivities to UV-B radiation enhancement, and the order fromhigh to low was Heterosigma akashiwo, Alexandrium tamarense and Skeletonemacostatum. Absorption spectra of acid methanolic extracts from 6 species of HABshowed 3 mains peak at 334 nm, 447 nm and 664 nm. MAAs's absorbption peak is334 nm and the others are chlorophyll a's absorbption peak.By comparing DNA polymorphism with RAPD technology, genetic similarityindex (S) for the two strains of Phaeocystis globosa collected from different waters ofShanTou ant Hong Kong was abtained. Our result indicated that they had the samekind of MAAs, and the genetic similarity index S=0.7. It was concluded that thatboth algae are different strains of Phaeocystis globosa.HPLC analysis showed that Alexandrium tamarense and Prorocentrumdonghaiense have more kinds and higher content of MAAs than other algae underPAR. With increase of UV-B exposure time, the contents of MAAs have a remarkableincrease, especially in Alexandriurn tamarense. Because of the high content of UVabsorbing compounds, they can more easily adapt the changing environment, such asenhanced UV-B radiation in the sunlight. Heterosigma akashiwo and Phaeocystisglobosa mainly have one kind of MAAs and only a slight increase of MAAs withUV-B enhancement. Although Skeletonema costatum and Chaetoeeros millelleri only have little MAAs, they are insensitive to UV-B radiation. Silicon contained in the cellwalls of Skeletonema costatum and Chaetoceros millelleri may play an important rolein preventing UV-B radiation.