Doctor of Philosophy, The Ohio State University, 2024, Earth Sciences

Atmospheric CO2 from global carbon emissions has increased at an unprecedented rate since the 1880s. Approximately 26% of atmospheric CO2 is absorbed into the surface ocean, resulting in a decrease in seawater pH referred to as ocean acidification. Additionally, increased atmospheric CO2causes the planet to warm, leading to ocean warming. Decreases in ocean pH and increases in ocean temperature negatively affect coral health, leading to decreased coral growth, cover, and biodiversity. Under future ocean acidification scenarios, the surface ocean is expected to decrease pH approximately 0.1 – 0.3 pH units, which leads to declining coral health. Calcification is energetically demanding, and when exposed to low pH corals need more fuel to maintain growth rates. Previous studies have shown a variety of responses to ocean acidification including decreased growth, decreased energy stores, or increased respiration. However, many of these effects are minimized when coral have access to food, which provides extra energy to the coral host. Most of these experiments are short or moderate-duration and do not study the long-term effects of ocean acidification to coral physiology and biogeochemistry. Therefore, volcanic CO2-vent ecosystems with naturally low pH can act as natural laboratories to study the effect of chronic ocean acidification on ecological time scales. The symbiotic coral Cladocora caespitosa and the asymbiotic coral Astroides calycularis grow at CO2-vents around the island of Ischia, Italy. To explore how these corals cope with low pH we 1) conducted a field survey of corals collected from ambient pH non-vent sites and low pH CO2-vent sites and 2) conducted a 6-month long experiment exposing corals collected from ambient and low pH sites to experimentally low pH. The field survey revealed that corals from CO2-vent sites have higher heterotrophic capacity than corals collected from ambient pH sites, allowing these corals to survive in a persistently low pH env (open full item for complete abstract)

Committee: Andréa Grottoli (Advisor); Jean-Pierre Gattuso (Committee Member); Elizabeth Griffith (Committee Member); William Lyons (Committee Member); Agustí Muñoz-Garcia (Committee Member) Subjects: Biogeochemistry; Biological Oceanography; Climate Change; Ecology; Environmental Science

Doctor of Philosophy, The Ohio State University, 2021, Earth Sciences

The distribution and abundance of coral reef ecosystems is declining globally due to the detrimental impacts of climate change. As the surface ocean becomes warmer and more acidic, corals must adapt or acclimatize in order to survive and persist. The overarching goal of my dissertation was to evaluate the biological processes that lead corals to adapt and acclimatize to the levels of ocean warming and acidification expected later this century. Following a review of 255 coral heat-stress experiments conducted over the last thirty years (Chapter 2), I identified several gaps in our knowledge of coral bleaching. For instance, the majority of experimental coral bleaching research has been conducted on only three Scleractinian coral species, many reef regions worldwide are critically understudied, and the literature is heavily biased towards adult life stages (as opposed to gametes, larvae, recruits). Similarly, the majority of studies are short-term in duration (i.e., < 7 days) and focus on only one or two aspects of coral biology (e.g., calcification or photosynthetic efficiency). Thus, our understanding of the long-term impacts of global climate change on coral holobiont physiology is lacking. To better understand the link between holobiont physiology and the environment, I conducted a comprehensive survey of Oʻahu coral reefs (Chapter 3), including eight species collected from six reef locations. I found that environmental gradients of temperature, significant wave height, and seawater chlorophyll concentration were strongly correlated with the physiological profiles of Hawaiian corals, though the strength of this relationship was species specific. My results indicate that Montipora capitata and Pocillopora acuta have the most physiological variance along environmental gradients, suggesting a higher capacity for adaptation or acclimatization. Conversely, Porites evermanni and Pocillopora meandrina have the least physiological variance which does not correlate strongl (open full item for complete abstract)

Committee: Andréa Grottoli (Advisor); Agustí Muñoz-Garcia (Committee Member); Lawrence Krissek (Committee Member); Robert Toonen (Committee Member); Noah Weisleder (Committee Member) Subjects: Biogeochemistry; Biology; Climate Change; Earth; Ecology; Environmental Science; Oceanography

Doctor of Philosophy, The Ohio State University, 2021, Earth Sciences

Increases in atmospheric CO2 are causing the planet to warm. As such, corals are living closer to their upper thermal tolerance limits, leading to decreased coral health and increased mortality. Increasing sea surface temperatures alter the symbiotic relationship between the coral host and endosymbiotic algae, causing coral bleaching. Such mass bleaching events are predicted to increase in frequency and severity over the next few decades. To protect at least 50% of coral reefs, warming would have to be limited to no more than 1.2°C. Thus, global warming presents an immediate threat to coral reefs. The continuing release of anthropogenic CO2 is also leading to ocean acidification (OA): the net dissolution of atmospheric CO2 into the surface ocean leading to decreases in seawater pH, net increases in total dissolved inorganic carbon and bicarbonate species, and a net decrease in carbonate species. OA is known to cause decreases in calcification in some, but not all corals, and can also be dose-dependent. Thus, the increasing temperature and OA in the ocean co-occur. While OA can exacerbate the negative effects of temperature stress on the physiological responses of some coral species, but not others, it is unknown if OA will impede or slow coral recovery from bleaching. Previous studies have shown that coral feeding on zooplankton may serve to mitigate bleaching or OA stress and enhance recovery from such events in some species. Corals acquire fixed carbon (i.e. food) and nutrients in three ways: 1) via photosynthetically fixed carbon translocated to the coral host from the endosymbiotic algae, 2) uptake of dissolved organic carbon by the coral animal's polyps, and 3) active eating of zooplankton and particulate organic matter by the coral polyps. While photosynthetically derived fixed carbon is critical to maintaining daily metabolism and calcification, heterotrophically derived food is critical for building lipid reserves and tissue growth. It is unknown if (open full item for complete abstract)

Committee: Andréa Grottoli (Advisor); Lawrence Krissek (Committee Member); Agustí Muñoz-Garcia (Committee Member); Robert Toonen (Committee Member); Michael Wilkins (Committee Member) Subjects: Climate Change; Environmental Science; Wildlife Conservation