Date of Award

Winter 11-19-2018

Level of Access Assigned by Author

Open-Access Thesis

Degree Name

Doctor of Philosophy (PhD)


Marine Biology


Susan Brawley

Second Committee Member

Nicholas Brown

Third Committee Member

William Halteman

Additional Committee Members

Vicki Hertzberg

Benildo de los Reyes

John Singer


This dissertation examines effects of stress on brown algal biology from a macroscopic scale by examining the whole aquaculture crops, and at a microscopic level by examining the macroalgal microbiome, across the vertical stress gradient of the intertidal zone and across the latitudes of their biogeographic ranges. Thermal stress negatively affected seedstock gametophytes of the kelp Alaria esculenta isolated from northern and southern locations in Maine. However, previous thermal stress had a positive effect on growth of the next-generation sporophytes. Alaria esculenta has potential as a kelp crop in Maine’s sea vegetable aquaculture sector and implementing this protocol may allow the sea vegetable industry to increase crop yields. Studies found that stress gradients that influence distributions of brown macroalgae, specifically Fucus spp., can affect the microbial composition of the macroalgal microbiome. Various methods of describing macroalgal microbiomes were examined with a common garden approach using a lab-cultured strain of Porphyra umbilicalis. Methods examined included different preservation techniques, differences between algal tissue types, variability across algal thallus, and microbial analysis programs. Results were applied to in situ studies of the natural microbiome of Fucus spp.: each species in the high, mid-, and low intertidal zones had a different microbiome. Manipulative transplants of mid-zone F. vesiculosus into the high zone assessed algal-associated bacteria tolerance to stress. Trans-Atlantic surveys of microbial diversity of F. vesiculosus found a biogeographic break in microbial community structure that correlated with sea surface temperatures and environmental stress across latitudes. These studies expand current knowledge of the direct and indirect effects of stress on phaeophytes across multiple scales.

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