Seasonal variations in phytoplankton productivity in a shallow cove in the eastern Seto Inland Sea, Japan
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ORIGINAL ARTICLE Environment
Seasonal variations in phytoplankton productivity in a shallow cove in the eastern Seto Inland Sea, Japan Hitomi Yamaguchi1 · Nozomi Koga1 · Kazuhiko Ichimi2 · Kuninao Tada1 Received: 17 March 2020 / Accepted: 10 September 2020 © Japanese Society of Fisheries Science 2020
Abstract We examined phytoplankton productivity in Shido Bay, an active oyster farming area in the eastern Seto Inland Sea, Japan, by an in situ 13C method from March 2016 to January 2017. The depth-integrated daily phytoplankton production ranged from 0.13 to 1.61 g C m−2 day−1, and the estimated annual production was 218 g C m−2 year−1. The daily production peaked in the rainy season and autumn, when phytoplankton blooms were observed, and production during the bloom events largely contributed to the annual production. There was a strong correlation between daily production and phytoplankton biomass (chlorophyll a) throughout the study period. In the study area, due to the shallow depth (6 m) and moderate light attenuation coefficient of the water column (0.38 ± 0.07 m−1), the mean light intensity in the water column was maintained at high levels (36 ± 5% of incident photosynthetically active radiation) throughout the study period. In contrast, the dissolved inorganic nitrogen concentration of the water was persistently low ( 0.05). The annual phytoplankton production was estimated to be 218 g C m−2 year−1.
Mean Chl a specific product. = 0.18 × Temp. + 0.24 ( ) (2) × Im − 1.95 R2 = 0.70, n = 14, p < 0.01 Both of the two explanatory variables were significant (p
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