2022 Volume 78 Issue 2 Pages I_655-I_660
Microphytobenthos are frequently the dominant primary producers in shallow tidal estuaries, and their photosynthesis is limited by the amount of photosynthetically active radiation (PAR). Most previous studies evaluating the primary production of microphytobenthos were conducted using “in-situ methods, ” which involve placing incubation bottles on tidal flats for certain durations (approximately 1 day). However, as in-situ methods do not reflect the variation in weather and tidal cycle; therefor, they may lead to errors in obtaining a representative value for a certain period (e.g., from month to year). In this study, we conducted field observation and laboratory experiments to estimate the primary production of microphytobenthos based on both P-I curve and mooring systems at two stations on Midori River tidal flats facing Ariake Bay, Japan, in October 2021. The monthly average primary production was compared with that recorded on days when the in-situ method was implemented, which corresponds to spring tide. Finally, we discuss the validity of the primary production estimated using the in-situ method as a representative value. The maximum photosynthetic activity and light saturation recorded in this study were much higher than those previous reported; hence, the microphytobenthos of the Midori River tidal estuary were considered to be adapted to relatively high light conditions. The average photosynthetic activity under high PAR (2493 µmol m−2s−1) was 4.80 mgC mgChl-a−1h–1 lower than that under moderate PAR (1246 µmolm−2s−1), indicating photoinhibition at one station. At the two sites where observations were conducted, the error from the average value exceeded by 10% in all except for two of the 16 cases, suggesting that the in-situ method estimates contain errors as representative values for the month.
