Temporal dynamics and spatial heterogeneity of microalgal biomass in recently reclaimed intertidal flats of the Saemangeum area, Korea

• Winter blooming of microalgae with high degree of spatial heterogeneity evidenced
• Spatial distribution of microalgal biomass was associated with macrofaunal zonation.
• Satellite-derived NDVI values well reflected in situ measured benthic chlorophylls.
• A proper sample size for reliable microalgal mapping suggested in regional scale.

Trophodynamics of intertidal mudflats are significantly driven by microphytobenthos (MPB) production but spatial and temporal dynamics of this production source is poorly known. To understand the temporal dynamics and spatial heterogeneity of intertidal MPB, benthic chlorophyll a, phaeopigments, and sediment properties were determined in Gyehwa (sandy) and Gwanghwal (muddy) tidal flats of Saemangeum area over a year at 97 stations. This study set out to: (i) characterize the spatial-temporal patterns in MPB biomass on a year-round basis, (ii) identify the abiotic and biotic factors associated with MPB distributions, (iii) investigate the use of satellite-derived chlorophyll a data and verify with in field measurements, and (iv) determine minimum required sample size for in situ biomass measurement. Concentrations of benthic chlorophyll a and phaeopigments were greater in winter and spring with a high magnitude of variance than in summer and fall at both areas. Benthic chlorophyll a and phaeopigments tended to decrease approaching lower tidal zone, being associated with the corresponding decrease in shore level and/or exposure duration. Compared to available data on macrozoobenthos distribution, the spatial variation of microalgal biomass seems to be attributed to distribution of deposit-feeders. A significant positive correlation (p < 0.001) between in situ MPB biomass and satellite-derived normalized difference vegetation index (NDVI) values was observed, but was much weaker in the lower tidal zone. Mirroring algal heterogeneity, the minimum required sample size for in situ biomass measurement were greater in blooming season and sandy bottom, suggesting that sampling design for spatio-temporal mapping of MPB should consider the sampling season and/or abiotic and biotic features of study area. Overall, spatio-temporal dynamics of intertidal MPB seem to be influenced by a combination of abiotic and biotic factors.