In situ' analysis of the biomass and distribution of microphytobenthos

Abstract

This thesis investigates the use of fluorescence techniques for the remote sensing of microphytobenthic biomass and distribution. Firstly, hardware was developed to facilitate the use of fluorometry for measuring microphytobenthos in situ. Comparisons between minimum fluorescence (Fo¹⁵) and chlorophyll a, as proxies for microalgal biomass, were made over varied seasonal and spatial scales. The relationship between Fo¹⁵ and Chl a was strongest for diatom dominated samples where micro-sections (0.2 mm) of sediment were sampled. No spatial patterns were found in diatom patch size or dispersion. The coefficient of variation between patches (using the proxy Fo¹⁵) made at scales from 2.5 - 500 cm, ranged from 5 to 150 %. The first non-destructive quantitative temporal study of microphytobenthos at the sediment surface (Fo¹⁵) was conducted. A proportion of the microphytobenthic community was found at the surface of the sediment during daylight tidal ebb and cells did not migrate from the surface at the end of tidal exposure. This has implications for re-suspension of cells during daylight immersion. Algal stress measurements (Fv/Fm) were unreliable at low biomass. The calculation of photosynthetic parameters from relative electron transport rate on undisturbed cores was found to be unrepresentative of those made in situ. The use of different units of expression for Chl a (both content and concentration) were investigated over temporal and vertical scales. Chl a content (μg Chl a g⁻¹ dry sediment) decreased over an emersion period. In contrast Chi a concentration (mg Chl a m⁻²) increased over this period. In this situation, contrasting Chi a determination could be wholly explained by the decrease in sediment water content over the period. These findings have implications for the estimation of biomass specific primary productivity.