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Abstract

Kelp are marine foundation species with high cultural and economic value, but they are threatened by climate change. One major influence on the general physiology and stress resistance of organisms is their bacterial community. Although a lot of research has been conducted on wild kelp populations, comparatively very little is known about how kelp associated bacteria respond to abiotic stress and even less is known about how commercial cultivation affects the kelp bacterial community. In this thesis, I address these gaps by testing how different environments and abiotic stressors affect the bacterial community of kelp. Chapter 2 tracks how the bacterial community of Saccharina latissima (sugar kelp) changes throughout the kelp cultivation cycle and incorporates other datasets of cultivated and wild kelp. In this chapter, I find that compared to the adult sporophytes, the microscopic stages of the kelp life cycle (gametophytes and juvenile sporophytes) have a very variable bacterial community that is strongly influenced by the environmental pool of bacteria. This points to different factors shaping the bacterial community at different stages of the kelp life cycle. Chapter 3 focuses on a novel disease in kelp nurseries, pink-spot disease. I identified a putative causative agent and through surveys of kelp growers, showed that pink-spot disease is common throughout the world. Chapter 4 combines field and lab data assessing the impact of abiotic stress (salinity and temperature) on the bacterial community of kelp. I found that the bacterial community of kelp is destabilized under stressful abiotic conditions. Overall, this thesis provides foundational biological knowledge about the stability of the kelp-associated bacteria community at all stages of the life cycle and advances knowledge of the bacteria associated with cultivated kelp that will advance kelp restoration and farming.