Impact of environmental factors on the life cycle and physiology of the green seaweed Ulva spp.

Sea lettuce Ulva spp., known for its worldwide distribution and remarkable growth rate, remains a largely under-exploited natural resource. Recently, this macroalga has established itself as a valuable biomass in aquaculture, thanks to its diverse applications in the food, feed, pharmaceutical, nutraceutical, biofuel and bioremediation sectors. Ulva's rapid growth and high capacity to assimilate carbon, nitrogen and phosphorus make it an attractive option for use as a biological filter. This project investigated the potential of Ulva for nutrient removal in brackish waters, focusing on the impact of reduced salinity on Ulva's metabolism. It also looked at the more fundamental biology of this genus, focusing on its primary carbon metabolism and the strategies it employs to maintain its rapid growth rate. Using isotopic 13C labelling, it was demonstrated that Ulva has a unique diurnal growth pattern, with a disconnect between the building of structural compounds occurring largely in the daylight, and cell expansion growth occurring at night. Then, extensive screening was conducted to identify Ulva strains that maintain valuable metabolic content and high growth rates under low salinity conditions, alongside with the development of a fast-screening method known as the “common-garden experiment”. This approach enabled the selection of the most suitable strains for the desired conditions in a reduced period of time, in a cost-effective way. Species and even strains varied significantly in their tolerance to low salinity, highlighting the importance of genetic/natural variation. A brief exposure to low salinity enhances the biochemical composition of Ulva, notably increasing carbohydrates in certain foliose species. This variability highlights the need for careful selection of species and strains to optimize Ulva biomass valorization for specific applications. In conclusion, the results presented in this thesis have advanced fundamental scientific knowledge of Ulva biology and provided insights into the use of Ulva spp. for nutrient removal in brackish waters.

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University of Galway

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Attribution-NonCommercial-NoDerivatives 4.0 International

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University of Galway Theses (PhD Theses)