Allelopathic Effect of Macroalga Gracilaria Tenuistipitata (Rhodophyta) on the Photosynthetic Apparatus of Red-tide Causing Microalga Prorocentrum micans

Under controlled indoor conditions, the red-tide causing microalga, Prorocentrum micans was co-cultured with varied grams of sheared macroalga Gracilaria tenuistipitata (Rhodophyta) in the coexistance culture system for three days, to characterize the mitigant roles by the seaweed in photosynthesis of the microalga. The polyphasic rising phase of fluorescence transients displayed by the oxygenic photosynthetic organisms at the initial illumination stage are named as OJIP. In this study, the transient flourescence curves of chlorophyll a with relevant parameters in P. micans were tracked precisely and clarified based on tests of JIP parameters to analyze photosystem II activity. The photosynthetic mitigant roles on P. micans by dried G. tenuistipitata on were obvirously gram- and time-relevant. Chl a fluorescence specific parameters followed the same patterns as the O-J-I-P profiles. Based on the transient flourescence curves with their relevant parameters, the main inhibitory sites by G. tenuistipitata on the photosynthetic appartus of P. micans might be listed as the decline in active numbers of photosystem reactive centers, coupled with blockng-up of the electron-transporting chain. From results of present study, it is clear that dried segments of G. tenuistipitata thalli have effectively inhibitory effect on photosynthesis of P. micans, indicating the potential algicide sources of the dried G. tenuistipitata for use against P. micans causing red tide.