Journal of Oceanography, Vol. 66 (No. 6), pp. 831-843, 2010
Tatsuya Shibata1*, Sarat C. Tripathy1 and Joji Ishizaka2
1Graduate School of Environmental Studies, Nagoya University, Chikusa-ku, Nagoya 464-8601, Japan
2Hydrospheric Atmospheric Research Center, Nagoya University, Chikusa-ku, Nagoya 464-8601, Japan
(Received 18 December 2009; in revised form 12 October 2010; accepted 12 October 2010)
Abstract: Underwater light environment and photosynthetic accessory pigments were investigated 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-harvesting pigments under higher light condition in the mixed layer caused by tidal cycle. Contribution rates of non-phytoplankton particles (anph(400-700)) for light attenuation coefficient (Kd) was highest (32-85%), and those of phytoplankton particles (aph(400-700)), dissolved organic matter (ag(400-700)) and water were 6-32, 6-21 and 5-23%, respectively. Mean Kd was higher during the spring tide (0.55 ± 0.23 m-1) than the neap tide (0.44 ± 0.16 m-1), and the Kd difference was caused by the substances 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 (). Moreover, there was significant negative correlation between ratios of light-harvesting pigments (fucoxanthin) per Chl a (Fuco/Chl a) and . 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.