Scientific discovery, technological revolutions, and complex global challenges are commonplace in the modern era. People are bombarded with news about climate change, pandemics, and genetically modified organisms, and scientific literacy has never been more important than in the present day. Yet only 29% of American adults have sufficient understanding to be able to read science stories reported in the popular press [Miller, 2010], and American students consistently rank below other nations in math and science [National Center for Education Statistics, 2012].

Chromatic acclimation by marine Synechococcus cyanobacteria is a colorful example of light-harvesting generalists, that change their phycoerythrin pigment to absorb blue (495 nm) or green (545 nm) light (type IV chromatic acclimation, or CA4). Though much is known about the molecular regulation of the trait, the ocean environment that selects for this acclimation strategy is not well understood. Similarly, the ecological costs of CA4 compared to Synechococcus strains with fixed pigment strategies (specialists) had not previously been investigated. This research used a combination of laboratory experiments, a competition model between Synechococcus generalists and specialists in simulated spectral environments, and comparisons with metagenomic and physical oceanographic in situ data from global ocean cruises, Argo floats, and satellites to address these gaps. Under experimental conditions, we show that blue-green generalists suffer an energetic cost across variable environments compared to specialists, and that all Synechococcus strains are twice as efficient in green light as in blue light. In model simulations, Synechococcus generalists had >70% correlation with deep mixed layers, but only 14% correlation with mixed layers in situ. Higher correlations were observed with low average mixed layer temperatures (< 14oC), low sea surface height, and large sea surface gradients, indicating upwelling zones and ocean fronts are important niches for generalists in the ocean. We propose that the main advantage of CA4 is not in direct competition with other Synechococcus strains, but in expanding the niche space of the genus into highly dynamic ocean environments.

In application of light color and pigment research to ecosystem management, the final chapter of this dissertation is a case study using the spectral shape produced by absorption and fluorescence of the marker pigment phycocyanin to detect cyanobacteria by field-based remote sensing. We test four algorithms to detect cyanobacteria blooms across a salinity gradient from freshwater to the Atlantic Ocean. We find that empirical algorithms centered around longer wavelengths in the red spectral region (~700 nm), such as Mean Peak Height for turbid waters, worked best for cyanobacteria detection and prediction. An expansion of this algorithm could be used to develop an early warning system for harmful cyanobacteria blooms in the region.

The combustion of fuels in the engines of ships releases inorganic compounds and metals that can promote phytoplankton growth (e.g. N, Fe, Mn, Zn) or decrease productivity (e.g. Cu). Many ship operators comply with air quality regulations by installing scrubber systems that clean emissions going into the air, but discharge washwater containing nutrients and contaminants directly into ocean water. This has the potential to change primary production rates and the structure of phytoplankton populations. Chapter 1 of the dissertation analyzed scrubber washwater samples from small engines combusting distilled fuels. Results revealed consistent enrichment of washwater with nitrogen and dissolved trace metals, with variations in the specific metals enriched. I compared our results to those found in the literature for a distilled fuel that was combusted in a small engine, and for residual fuels combusted in large ship engines. Using diverse model simulations, Chapter 1 demonstrated that cumulative scrubber water discharges could fertilize phytoplankton in specific regions by providing essential nutrients like iron. In Chapter 2, I presented results from mesocosm experiments simulating acute exposure of coastal phytoplankton to high concentrations (1%, 5%, and 10%) of scrubber washwater from engines using both distilled and residual fuels. Growth responses varied across phytoplankton taxa and fuel types, providing insights into potential ecological consequences in heavily trafficked coastal regions. Chapter 3 explored the impact of scrubber washwater discharges on natural phytoplankton communities in the Sargasso Sea. Both conventional heavy fuel oil (HFO) and alternative distilled fuel (HGO) exhibited mild fertilizing effects at a 2% concentration. This chapter emphasized co-limitation by multiple nutrients, with scrubber washwater at 2% adequately supplying nutrients compared to lower concentrations. This dissertation highlights the complex interactions between ship emissions, scrubber washwater, and marine ecosystems, emphasizing the need for comprehensive assessments to inform sustainable maritime practices.