Microphytobenthos (MPB) biomass variability and sediment- water column exchanges on an intertidal flat: Influence of weather-related abiotic factors across neap-spring-neap tidal cycles

The spatio-temporal distribution of microphytobenthos (MPB) on the sediment surfaces during emersions and suspended in water column during immersions was investigated on transects across Fingringhoe Tidal Flat in Colne estuary, on three zones: the mud flat, the transition zone and the salt marsh. The results of this thesis suggest that MPB distribution on intertidal flat was controlled by a set of complex interaction between the MPB with both biotic and abiotic factors. How much MPB are there on the sediment surfaces determines the availability of MPB biomass after immersion period and in the water column during immersion. ‘Sum of sun hours’ and ‘sum of rainfall’ directly affected the MPB biomass on sediment surfaces, and consequently, indirectly affected the MPB that associated with suspended sediment in the water column during immersions. Tidal range did not have significant effect on MPB biomass on sediment surfaces, however was significantly negatively effected the suspended MPB on the mud flat and the transition zone. The Chl a on the salt marsh however was significantly positively correlated with the tidal range. Data of net settlement rate of suspended sediment per hour during immersions displayed positive relationship with MPB biomass availability after immersion. The sediment settlement on the intertidal flat was negatively correlated with mean wind speed and tidal range. Neap-spring-neap tidal cycles were found to nfluence MPB species composition across the tidal flat. Spring tide that was characterized by high water current and high tidal range (4.3 – 5.6 m) showed to increase the occurrence of centric diatom such as species from genus Coscinodiscus, genus Actinoptychus and Odontella on both mud flat and transition zone. Also, the spring tide was responsible to source the salt marsh with species that commonly recorded on the mud flat and transition zone such as Pleurosigma angulatum and species from genus Gyrosigma.