Examining the physiology of harmful microalgae during algicidal control and diel vertical migration
Date
2014
Authors
Tilney, Charles L.
Journal Title
Journal ISSN
Volume Title
Publisher
University of Delaware
Abstract
The frequency of harmful algal blooms (HABs) has increased, and so too has the societal and environmental costs associated with them. Anthropogenic eutrophication has played some part in this, but is not always implicated, as HABs and their drivers are diverse. Continued investigation into HAB biology and ecology may help to identify the underlying factors controlling algal blooms in general, and factors implicated in their recent increase in particular. Investigation of the various methods for the prevention, control, and mitigation of HABs is also warranted, to identify 'solutions' to reduce or eliminate some or all of the costs imposed by HABs. In this dissertation, both basic and applied work was conducted, initially on the control of dinoflagellates with a sterile bacterially-derived algicidal filtrate that is strongly specific toward dinoflagellates, and then on the diel vertical migration (DVM) of two potentially harmful species of microalgae. Initial investigations of the algicidal filtrate (termed IRI-160AA) assessed the effects in cultured dinoflagellates, and identified that electron transport through the photosynthetic apparatus at photosystem II (PSII) was broadly inhibited in algicide treated dinoflagellates. Moreover, IRI-160AA induced dose-dependent effects on both cell viability and PSII efficiency, and although dinoflagellate responses were highly species specific, one apparent generalization was that thecae reduced overall susceptibility. Next, the algicidal filtrate was tested on field collected water samples containing dinoflagellates. These dinoflagellates were less susceptible than uni-algal cultures because they were not in the most susceptible phase of growth, which corroborated the idea of Pokrzywinski et al. (2012) that identifying the growth stage of dinoflagellate blooms in the field would be crucial to achieving high levels of bioactivity with the algicide. Using a combination of polymerase chain reaction denaturing gradient gel electrophoresis (PCR-DGGE) and quantitative real-time PCR, I determined what changes occurred in the eukaryotic and prokaryotic microbial communities after applications of IRI-160AA. A common theme among these applications was the rise of bactivorous protists, most notably Paraphysomonas spp., which likely arose as a response to bacterial growth from dissolved organic matter (DOM) within the filtrate and released from dying dinoflagellates. This result highlighted how the microbial loop might transfer dinoflagellate carbon back to higher trophic levels in large-scale applications, and perhaps in HAB control more generally. The results suggest that IRI-160AA could be a potent and species-specific method to control harmful dinoflagellates in nature, but future work is required to identify methods to appropriately and cost-effectively scale- up algicide production, as well as to isolate the active compounds and determine the molecular targets and mode of action. Finally, a detailed comparison of the diel vertical migrations (DVM) of two sympatric harmful algal species (Karlodinium veneficum and Chattonella subsalsa ) was conducted in laboratory columns under various sampling regimes and lighting conditions. Both species exhibited markedly different DVM patterns, which were consistent with different photoprotective mechanisms, and carbon assimilation rates. DVM was found to be under the control of a circadian clock in C. subsalsa but not K. veneficum. This work provides a useful comparison between two potentially harmful species from the Delaware Inland Bays, and improves our understanding of the niches that these algae are adapted to. Collectively, this dissertation has raised many interesting questions for future research addressing the control of harmful algae with biologically derived compounds, and laid important foundations for deeper investigations into the role of diel vertical migration in two cosmopolitan harmful algae.