Date Approved

12-2020

Graduate Degree Type

Thesis

Degree Name

Biology (M.S.)

Degree Program

Biology

First Advisor

Dr. Kevin B. Strychar

Second Advisor

Dr. Daniel Barshis

Third Advisor

Dr. Sarah Hamsher

Fourth Advisor

Dr. Briana Hauff-Salas

Academic Year

2020/2021

Abstract

Over the years, global warming has had a devastating effect on coral reef ecosystems. Anthropogenic influences have caused significant increases in greenhouse gases, with a subsequent increase in solar radiation held within Earth’s atmosphere leading to increasing global temperatures. The increasing temperatures from concurrent increases in greenhouse gases impact fragile marine ecosystems such as coral reefs, which require particular environmental parameters such as temperature in order to survive and maintain a diverse ecosystem in which many marine species rely on. These increases in temperature exacerbate phenomena such as bleaching events and coral disease, drastically impacting coral on a global scale and with the threat of extinction. However, most research has been focused on corals in tropical/subtropical systems. Corals within temperate systems have been studied less-so in terms of how global warming will impact their physiology and future survivorship. This thesis focuses on the temperate coral, Astrangia poculata, with colonies collected from Narragansett Bay in Rhode Island, USA, to understand how this species will respond to increased temperatures and disease exposure. This thesis will focus on two separate experiments, one primarily on heat stress, and the other on understanding disease impacts and its relation to elevated temperatures. The heat stress experiment subjected colonies of A. poculata to treatments of ambient and increased temperatures over a period of ten days to understand the accumulation of reactive oxygen species (ROS), a toxic chemical byproduct of bleaching mechanisms within Photosystem II (PSII) in symbiotic algae. Measurements of maximum quantum yield via pulse amplitude modulation fluorometer techniques (i.e. to assess photosynthetic health of A. poculata’s algal symbiont) and photo quantification via Winters et al. (2009) (i.e. to determine symbiont density) were taken to compare to ROS concentrations measured using imaging flow cytometry (IFCM). Results from 5 this experiment found that ROS concentrations from elevated temperature treatments were lower compared to ambient temperature treatments, albeit no statistical significance was found. No statistical differences between elevated and ambient temperature treatments were found within maximum quantum yield, indicating the possible influence of increased nitrogen exposure and endolithic algae. In addition, differences between treatments found in pixel intensity results (i.e., symbiont density via photo quantification) suggest influence by seasonality and endolithic algae. The results from this experiment suggest that A. poculata be considered a resilient coral species to future elevated temperatures.

The second experiment was to determine the influence of temperature on the baseline immunity of symbiotic and aposymbiotic A. poculata, as no previous studies have identified immune responses within A. poculata. The use of lipopolysaccharide (LPS) provide a general understanding of immunity within this species as a substitute for a pathogen. The exposure of LPS was set to measure the signaling protein prophenoloxidase (PPO) and melanin within the melanin-synthesis pathway to determine an immune response. Astrangia poculata fragments were exposed to LPS for a 12-hour period at two different temperatures, ambient (18 °C) and elevated (26 °C). Melanin was significantly higher within symbiotic corals compared to aposymbiotic corals and no statistical difference was found with regard to PPO concentration, suggesting that this species is susceptible to disease at elevated temperatures. The difference in response based on symbiotic state suggests the influence of other potential immune responses, such as the complement pathway and the coral microbiome. With the lack of differences found in PPO and response differences found between symbiotic state, this research recommends future projects into other immune responses to determine the holistic immune system within A. poculata.

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