Short-term variability of microphytobenthic primary production associated with in situ diel and tidal conditions Bong-Oh Kwon a , Jong Seong Khim b, * , Jinsoon Park b , Jongseong Ryu c , Seong-Gil Kang d , Chul-Hwan Koh a a School of Earth and Environmental Sciences (Oceanography), Seoul National University, Seoul 151-742, Republic of Korea b Division of Environmental Science and Ecological Engineering, Korea University, Anam-dong, Seongbuk-gu, Seoul 136-713, Republic of Korea c Department of Marine Biotechnology, Anyang University, Ganghwa-gun, Incheon 417-833, Republic of Korea d Maritime & Ocean Engineering Research Institute (MOERI)/Korea Institute of Ocean Science and Technology (KIOST), Daejeon 305-343, Republic of Korea article info Article history: Received 20 November 2011 Accepted 29 July 2012 Available online 4 August 2012 Keywords: microphytobenthos tidal flat oxygen microsensor benthic productivity endogenous rhythm abstract The short-term variability in microphytobenthos (MPB) production, measured by the oxygen micro- profiling method, found under different experimental conditions indicated an endogenous production response reflecting in situ diel and tidal conditions. MPB production was measured for submerged core samples (collected from Daebu mudflat, Korea) at a fixed irradiance and temperature in the laboratory under the conditions of (1) constant light (data-I), (2) lightedark incubation (data-II), and (3) in situ reflected (data-III). The experimental design aimed to characterize within-day, across-day, and long term changes in MPB production. Our results showed that, under constant light conditions for 72 h, temporal fluctuations in MPB production (day:night ¼ 2.4:1) were clearly present for three consecutive days (data- I), indicating a diel rhythm in production. Production increased at the beginning of light exposure, and dramatically decreased at the time of submersion, indicating tide-dependent rhythm in production. Furthermore, over a 10 d period under the same light and temperature conditions, a weakening (declining) trend in production was observed, which was logarithmic with diel fluctuation (r 2 ¼ 0.995, p < 0.01). This diel rhythm in production was also observed under an alternating lightedark (L 14 h /D 10 h ) incubation period across an additional 18 d of measurement (data-II). The decline in production was slower, and more linear (r 2 ¼ 0.930, p < 0.01) under this condition, as the period of dark incubation (D 10 h ) seemed to allow the community to recover to a certain level of production. Finally, the effects of tidal condition (spring tide vs. neap tide) and biomass (dense vs. lesser dense) on the short-term (<hourly) variability of MPB production (data-III) appeared to be negligible when time integrated the production. Ó 2012 Elsevier Ltd. All rights reserved. 1. Introduction Microphytobenthos (MPB) plays a key ecological role in coastal ecosystems, as they contribute a significant amount (up to 50%) of the total estuarine carbon budget (De Jonge and van Beusekom, 1992; Underwood and Kromkamp, 1999). In particular, benthicepelagic interactions generate a significant contribution to the productivity in water column in areas where MPB is distributed, serving as important food sources for both benthic and pelagic herbivores (De Jonge and van Beusekom, 1992; Koh et al., 2007). The intertidal environment is subject to dynamic environmental changes, due to alternations in light/dark cycles, submersion/ emersion, and resuspension/sedimentation (Koh et al., 2006; Denis and Desreumaux, 2009). Such environmental conditions are expected to result in both temporal and spatial changes in MPB assemblages. For example, in the macrotidal environment, certain parameters, such as irradiance and temperature, vary temporally within a tidal cycle, resulting in dynamic changes in MPB biomass and production (Barranguet et al., 1998; Serôdio and Catarino, 1999). Previous studies have successfully demonstrated that within-day variations of in situ MPB production are strongly influenced by tidal effects (Miles and Sundbäck, 2000; Blanchard et al., 2001; Blanchard et al., 2002; Tolhurst et al., 2003; Blanchard et al., 2006; Spilmont et al., 2007). While many studies have demonstrated such short-term variations in MPB biomass, they have mostly focused on vertical migration (Consalvey et al., 2004). Within-day production and associated factors at shorter time scales, such as several minutes to hours, have * Corresponding author. E-mail address: jongseongkhim@korea.ac.kr (J.S. Khim). Contents lists available at SciVerse ScienceDirect Estuarine, Coastal and Shelf Science journal homepage: www.elsevier.com/locate/ecss 0272-7714/$ e see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.ecss.2012.07.029 Estuarine, Coastal and Shelf Science 112 (2012) 236e242