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The trace element selenium (Se) is required for the biosynthesis of selenocysteine (Sec), the 21st amino acid in the genetic code, but its role in the ecology of harmful algal blooms (HABs) is unknown. Here, we examined the role of Se in the biology and ecology of the harmful pelagophyte, Aureococcus anophagefferens, through cell culture, genomic analyses, and ecosystem studies. This organism has the largest and the most diverse selenoproteome identified to date that consists of at least 59 selenoproteins, including known eukaryotic selenoproteins, selenoproteins previously only detected in bacteria, and novel selenoproteins. The A. anophagefferens selenoproteome was dominated by the thioredoxin fold proteins and oxidoreductase functions were assigned to the majority of detected selenoproteins. Insertion of Sec in these proteins was supported by a unique Sec insertion sequence. Se was required for the growth of A. anophagefferens as cultures grew maximally at nanomolar Se concentrations. In a coastal ecosystem, dissolved Se concentrations were elevated before and after A. anophagefferens blooms, but were reduced by >95percent during the peak of blooms to 0.05 nM. Consistent with this pattern, enrichment of seawater with selenite before and after a bloom did not affect the growth of A. anophagefferens, but enrichment during the peak of the bloom significantly increased population growth rates. These findings demonstrate that Se inventories, which can be anthropogenically enriched, can support proliferation of HABs, such as A. anophagefferens through its synthesis of a large arsenal of Se-dependent oxidoreductases that fine-tune cellular redox homeostasis.

Harmful algal blooms (HABs) are an escalating problem in coastal ecosystems, inflicting massive economic losses on commercial fisheries and causing death and illness to both humans and marine fauna. Paralleling the rise of marine HAB problems, cyanobacteria (previously identified as "blue-green algae") have a worldwide distribution and can form extensive blooms in freshwater and estuarine habitat. Microcystins are fast becoming a global health concern, with severe and recurrent blooms with toxin elaboration reported globally, including central California. Until recently, microcystin intoxication was considered a public health issue mainly of freshwater habitat, reflected by the vast body of published literature on potential human health risks due to microcystin exposure in rivers, lakes, reservoirs and freshwater aquaculture. In contrast, monitoring of marine water and seafood for similar risks has been limited, despite confirmation of outflows of microcystin-contaminated freshwater to the ocean. A passive sampling method for determination of dissolved toxins in seawater, Solid Phase Adsorption Toxin Tracking (SPATT), allows for field-deployment of adsorbent resin sealed within a polyester mesh bag and have been used for a suite of lipophilic toxins, but until recently have never been evaluated for use with hydrophilic (water-soluble) toxins such as domoic acid (amnesic shellfish poisoning) and saxitoxin (the primary toxin associated with paralytic shellfish poisoning).

This dissertation provided novel insights on the dynamics and consequences of harmful algal blooms (HABs) in the California Current System (CCS). Parasitism is described as a biological control agent of harmful dinoflagellate blooms and referred to as a novel factor influencing HAB dynamics in coastal upwelling environments. Chapter 1 documented, for the first time, the presence of Amoebophrya, an endoparasitic dinoflagellate that infects and kills 7 bloom-forming dinoflagellate host species that occur throughout the CCS. Chapter 1 also discussed parasitism effects on (1) host population dynamics, (2) dinoflagellate species diversity, (3) net phytoplankton community composition and (4) trophic web structure within the planktonic community of an upwelling environment. Chapter 2 specifically verified the role of such a parasite in controlling harmful dinoflagellate blooms caused by one of its hosts in Monterey Bay. Findings of Chapter 2 suggested that blooms might develop when the host ‘escapes’ parasitism by Amoebophrya. In contrast, epidemic parasitic outbreaks may contribute to stoping or preventing the occurrence of dinoflagellate harmful blooms. Chapter 3 and 4 focused on the consequences of HABs caused by diatoms of the genus Pseudo-nitzschia, which cannot be parastitized by Amoebophrya and produces the neurotoxin domoic acid (DA). Chapter 3 verified that human consumers of recreationally-caught fishes can be exposed to asymptomatic doses of domoic acid. Lastly, Chapter 4 dealt with the hypothesis that the pelagic predator Humboldt squid (Dosidicus gigas), which recently invaded the domains of CCS, is exposed to domoic acid. However, beach strandings of this species in Southern California could not be linked to domoic acid exposure and was likely related to other unknown causes.