Phytoplankton Pigment Change as a Photoadaptive Response to Light Variation Caused by Tidal Cycle in Ariake Bay Japan

摘要

Underwater light environment and photosynthetic accessory pigments were investi-gated in Ariake Bay in order to understand how change of the pigments occurs in response to the tidal-induced changes in underwater light conditions. We hypothesize that phytoplankton increases photo-protective pigments and decreases light-harvest-ing pigments under higher light condition in the mixed layer caused by tidal cycle. Contribution rates of non-phytoplankton particles (a_(nph)(400-700)) for light attenua-tion coefficient (K_d) was highest (32-85%), and those of phytoplankton particles (a_(ph)(400-700)), dissolved organic matter (a_g(400-700)) and water were 6-32,6-21 and 5-23%, respectively. Mean K_d was higher during the spring tide (0.55 ± 0.23 m~(-1)) than the neap tide (0.44 ± 0.16 m~(-1)), and the K_d difference was caused by the sub-stances resuspension due to the tidal current. In contrast, ratios of photo-protective pigments (diadinoxanthin and diatoxanthin) per chlorophyll a ((DD+DT)/Chl a) were higher during the neap tide (0.10 ± 0.03 mg mg-Chl a~(-1)) than the spring tide (0.08 ± 0.03 mg mg-Chl a~(-1)). And there was significant positive correlation between (DD+DT)/ Chl a and mean relative PAR in the mixed layer (I_(mix) ). Moreover, there was signifi-cant negative correlation between ratios of light-harvesting pigments (fucoxanthin) per Chl a (Fuco/Chl a) and I_(mix) . These results suggested that phytoplankton in Ariake Bay increase photo-protective pigments and decrease light-harvesting pigments in the higher light condition of less turbid, shallower mixed layer during neap tide than spring tide.