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Intertidal biofilm is a thin layer of microbes and meiofauna enmeshed in an extracellular polymeric matrix within and on top of mudflat sediment. This medium provides a dynamic resource for a variety of consumers in estuarine habitats, and is rich in essential fatty acids that birds require for long-distance migration. We measured seasonal changes in biofilm fatty acid content from spring to summer on the Fraser River Estuary, one of the richest and most important ecosystems for migrant and wintering waterbirds in Canada. Fatty acid content in biofilm showed a strong seasonal pattern with a peak in the spring that is associated with the northward migration of Western Sandpipers (Calidris mauri) to their breeding grounds. This peak is linked to the abundance and physiological state, and hence nutritional condition, of epipelic diatoms, which, in turn, depend on a combination of mudflat topography, salinity, temperature, and nutrients that can fluctuate widely with the freshwater inputs from the Fraser River. Specifically, areas with higher elevation (i.e., ∼1 m) had longer periods of exposure to ambient conditions (i.e., light, warm temperatures, gas exchange into/out of biofilms) that facilitated more biofilm growth and higher fatty acid content. Moreover, springtime changes in water chemistry (i.e., salinity/osmotic stresses and nutrients) and temperature facilitated the production of higher overall total lipid/fatty acid contents in the mudflat biofilms compared to summer. Effective conservation of migrating shorebirds depends on the protection of underlying processes at important stopover sites that promote biofilm communities to escalate their production of lipids, including essential fatty acids, during key times of the year.

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Algae biofilms were grown in a semicontinuous flat plate biofilm photobioreactor to study the effects of light direction and suspended algal cell populations on algal biofilm growth. It was determined that, under the growth conditions and biofilm thicknesses studied, light direction had no effect on long-term algal biofilm growth (26 days); however, light direction did affect the concentration of suspended algal cells by influencing the photon flux density in the growth medium in the photobioreactors. This suspended algal cell population affected short-term (7 days) algae cell recruitment and algal biofilm growth, but additional studies showed that enhanced suspended algal cell populations did not affect biofilm growth rates over the long term (26 days). Studying profiles of light transmittance through biofilms as they grew showed that most of the light became attenuated by the biomass after just a few days of growth (88 % after 3 days). The estimated biofilm thicknesses after these few days of growth were approximately 150 μm. The light attenuation data suggests that, although the biofilms grew to 700-900 μm, under these light intensities, only the first few hundred micrometers of the biofilm is receiving enough light to be photosynthetically active. We postulate that this photosynthetically active layer of the biofilm grows adjacent to the light source, while the rest of the biofilm is in a stationary growth phase. The results of this study have implications for algal biofilm photobioreactor design and operation.