Date

Spring 2026

Document Type

Master's Thesis (Open Access)

Degree Name

Master of Science (M.S.)

Department

Moss Landing Marine Laboratories

Abstract

Mercury is a potent neurotoxin that bioaccumulates and biomagnifies in marine environments. Most research on mercury cycling in the ocean focuses on pelagic food webs, leaving a gap in knowledge regarding macroalgal-based food webs. Seaweed from the genus Ulva is globally distributed in marine and brackish habitats, accumulating metals and toxins with minimal impact on the host. While the mechanisms behind Ulva's tolerance to marine pollution are unclear, studies suggest that the macroalgal microbiome may play a crucial role. This study investigates how collection location influences mercury uptake and bacterial community composition in Ulva. Estuarine and coastal Ulva were exposed to 1, 50, and 200 ng/L of mercury in 6-day laboratory experiments. Total mercury concentrations were measured using a Direct Mercury Analyzer-SO, while the Ulva microbiome's taxonomic composition was estimated from the V3-V 4 regions of the 16s rDNA gene. Results indicated that estuarine samples accumulated higher mercury concentrations than coastal samples (PERMANOVA, p < 0.001). The microbial community structure differed between coastal and estuarine Ulva samples at various taxonomic levels (PERMANOVA, p = 0. 1). Differential abundance analysis revealed that 81 operational taxonomic units (OTUs) from 8 classes were enriched in coastal Ulva, while 147 OTUs from 12 classes were enriched in estuarine Ulva. This study demonstrates that the Ulva microbiome and mercury uptake are influenced by habitat. Additionally, the microbiome differences due to habitat may affect mercury uptake. Although the microbiome of Ulva in estuarine environments may enhance the macroalgal holobiont's resilience to nutrient and toxin loads, host health must also be considered given the toxicity of mercury and the lower accumulation observed in coastal Ulva populations.

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