Seasonal Variation of Primary Productivity in Shitaba Bay of Uwa Sea, Japan

Abstract

Primary productivity in the Shitaba Bay of Uwa Sea was measured by the in situ ¹³C tracer method one to three times a month for three years from February 2002 to January 2005, together with the hydrographic observation and chlorophyll a and nutrients analysis. The depth-integrated primary productivity ranged from 0.11 gCm^-2 day^-1 to 1.83 gCm^-2 day^-1 during the observation, and the annual primary productivity was estimated to be about 193 gCm^-2 year^-1. The productivity was highest in summer (0.82 gCm^-2 day^-1) throughout the year, followed by that of autumn (0.68 gCm^-2 day^-1), spring (0.44 gCm^-2 day^-1), and was lowest in winter (0.18 gCm^-2 day^-1). There was a correlation (r=0.77, p<0.01) between the primary productivity and depth-integrated chlorophyll a (mgm^-2) throughout the year, and high correlation (r=0.96, p<0.01) was found in autumn but no correlation was found in summer. The chlorophyll a specific productivity generally tend to increase with the surface irradiance, but in summer the chlorophyll a specific productivity was considerably variable, probably due to the different nutrient availability. High chlorophyll a specific productivity may be linked to the intrusion of bottom water, which may play an important role in supporting the biological productivity of Shitaba Bay.