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Thesis/Dissertation
Date
2025-05
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Biology
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DOI
https://doi.org/10.34944/awf0-cb55
Abstract
Anthropogenic-driven change is widely considered the largest threat to global ecosystem health and function, with consequences that are of particular significance to aquatic ecosystems. Specifically, the global increase in microplastic production, accumulation, and deposition are now recognized as a serious pollution hazard, much of which makes its way into aquatic systems. Microplastics, traditionally defined as plastic within the range of 5 mm to 0.1 µm, have been shown to interact with local organisms, both large and small, with differing results. Some of the latest findings revealed protists colonize, ingest, and egest microplastics in both in situ and laboratory conditions. In this dissertation, the consequences of both direct and indirect microplastic exposure with mixotrophic protists, those that are both photosynthetic and phagotrophic are assessed. Current literature indicates microplastic distribution in the oceans to be ubiquitous, reaching from coastal communities to the deepest depths of the Mariana Trench. However, their distribution is not homogenous, with current studies showing elevated levels of microplastics near coastal regions compared to offshore stations. Relatively few studies have investigated microplastics in the Southern Ocean, but surveys indicate the presence of plastic pollution in several oceanic areas surrounding the continent. This dissertation expands on those investigations by enumerating the total microplastic pollution during two seasons at a single oceanic station off the Western Antarctic Peninsula, plus for the first time, identifying the types of plastic polymers within three size fractions (0.22 – 20 µm, 20 – 100 µm, and > 100 µm) across several depths. Another anthropogenically driven change is the global rise of temperature. Within the Southern Ocean, the effects of elevated temperatures are associated with reduced ice formation, longer growing seasons, and potentially a novel thermocline not characteristic of the Antarctic maritime, indicative of altered light regimes and nutrient availability. Current projections suggest a regional response shifting in the microbial community from larger protists (i.e., diatoms) to smaller pico- and nanoplankton (i.e., cryptophytes and/or mixed flagellates), a trend that’s starting to occur in the Western Antarctic Peninsula (WAP) region. Many of these smaller flagellates are mixotrophic, which is the ability to utilize both photosynthesis and phagocytosis. Lastly, I reveal the impact of mixotrophic nanoplankton throughout the WAP region by assessing their distribution, activity (utilizing a novel approach to estimate their role as a bacterivore and their ever-elusive role as a primary producer), and the percent of the mixotrophic carbon demand input from either bacterivory or primary production in situ. The results of this study will aid in the understanding of the balance between phagotrophy and phototrophy in Antarctic mixotrophs, how microplastics may impact the mixotrophic community, and help to parameterize predictive models of microbial communities response to increasing microplastic pollution.
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