Graduation Year

2022

Document Type

Thesis

Degree

M.S.

Degree Name

Master of Science (M.S.)

Degree Granting Department

Marine Science

Major Professor

Christopher D. Stallings, Ph.D.

Committee Member

Isabel C. Romero, Ph.D.

Committee Member

Nicole D. Fogarty, Ph.D.

Keywords

Marine debris, Ocean warming, Plastic pollution, Time trend, Zooxanthellae density

Abstract

Microplastics have accumulated in the environment since plastic production began. They have spread to all areas of the globe from marine trenches to mountains and they can be harmful to organisms. However, research on microplastics has only recently begun so it is unclear how they have changed over time in many regions of the ocean and how current oceanic concentrations might affect marine life. Additionally, organisms such as corals are under stress and have been declining due to climate change, so it is not yet known if microplastics exacerbate these threats. My thesis addressed these gaps in the literature by assessing the temporal and spatial dynamics of microplastics in an understudied basin as well as how current oceanic concentrations, in combination with thermal stress, affect the bleaching response of an important coral species. To assess how microplastics have changed over time and space in the Gulf of Mexico, I used agglutinated foraminifera from sediment cores that incorporated the pollutant into their tests. I found that microplastics were higher after plastic production began, which was an expected temporal trend. I also found a spatial pattern where microplastic concentrations were higher at deeper sites as well as those close to the Mississippi River. Then, I assessed how microplastics interacted with thermal stress in corals using a controlled laboratory experiment. I exposed fragments of the threatened Caribbean coral, Acropora cervicornis, to orthogonally crossed treatment levels of microplastic beads (0 and 11.8 particles L-1) and water temperatures (ambient at 28°C and elevated at 32°C), then quantified zooxanthellae densities to measure the bleaching response. Regardless of microplastic treatment level, corals in the elevated temperature treatment were visibly bleached and necrotic (i.e., significant negative effect on zooxanthellae density) while those exposed to ambient temperatures remained healthy. However, there was not a significant microplastic effect at either individual (ambient temperature) or combined levels (elevated temperature). My thesis adds to the emerging literature on microplastics in the Gulf of Mexico and their effects on corals. Importantly, my study was the first to assess their temporal and spatial dynamics in deeper-water sediments in the GOM. Also, I used environmentally relevant microplastic concentrations to understand how current conditions affect corals. Additional work is needed to more fully identify the distribution of microplastics across the Gulf of Mexico to better understand how sensitive ecosystems are affected by this pollutant.

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