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Full text release has been delayed at the author's request until August 04, 2027

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Heterotrophy promotes coral resilience to ocean acidification and ocean warming

Hulver, Ann Marie
http://orcid.org/0000-0003-0466-9070
http://rave.ohiolink.edu/etdc/view?acc_num=osu1721126280854349

Abstract Details

2024, Doctor of Philosophy, Ohio State University, 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 environment. The 6-month ocean acidification experiment revealed that corals sourced from ambient pH sites maintain energy reserves, but not heterotrophy, in response to low pH. These results suggest that corals collected from ambient pH sites have decreased heterotrophic input and may not survive for longer than 6 months in low pH. However, there is evidence of acclimatization or adaptation of CO2-vent collected corals to low pH. Ocean warming is the second global stressor impacting corals. Corals already live near their thermal maximum and increases of only +1°C for 10 days can lead to coral bleaching. With continued use of fossil fuels sea surface temperatures are expected to increase ~3°C by the year 2100, which could cause ocean-wide declines in coral cover and biodiversity. However, some corals are more resilient to increases in temperatures due to high baseline heterotrophy, heterotrophic plasticity, high energy reserves, or the presence of thermally tolerant endosymbionts. The coral Stylophora pistillata from the Red Sea has shown incredible resilience to heat stress in previous experiments, surviving up to 32 degree-heating weeks due to high baseline heterotrophy and high energy reserves. To explore how S. pistillata copes with shifts in baseline temperatures, we conducted a 6-month long experiment, exposing this coral to chronic warm, but sub-bleaching temperatures. S. pistillata survived throughout the 6-month experiment with minimal physiological differences and sustained heterotrophy throughout. Corals were initially affected by warmer temperatures, but largely acclimated by the end of the six months. However, decreases in the ratio of photosynthesis to respiration and growth, indicate a non-lethal cost to long-term exposure to even moderate increases in temperature. Overall, the findings of this dissertation research suggest that corals with high baseline heterotrophy are able to cope with ocean acidification or ocean warming. Both C. caespitosa and A. calycularis from the Mediterranean are able to survive in persistently low pH environments due to their high heterotrophic capacity and may form source populations for nearby ambient pH populations. S. pistillata can acclimate to chronic shifts in baseline temperature in part because it maintains feeding. However, even in this most resilient coral species, the coral metabolism and growth is compromised under baseline temperature increases suggesting that while this species will persist, it may not thrive under future ocean conditions. The results from this dissertation suggest that corals with high baseline heterotrophy will persist longer in a changing ocean, giving these resilient coral populations a chance to acclimatize to warmer and more acidic oceans.
Andréa Grottoli (Advisor)
Jean-Pierre Gattuso (Committee Member)
Elizabeth Griffith (Committee Member)
William Lyons (Committee Member)
Agustí Muñoz-Garcia (Committee Member)
236 p.
Biogeochemistry; Biological Oceanography; Climate Change; Ecology; Environmental Science
coral; ocean acidification; climate change; ocean warming; heterotrophy; radiocarbon; Mediterranean; resilience;

Recommended Citations

Citations

  • Hulver, A. M. (2024). Heterotrophy promotes coral resilience to ocean acidification and ocean warming [Doctoral dissertation, Ohio State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=osu1721126280854349

    APA Style (7th edition)

  • Hulver, Ann. Heterotrophy promotes coral resilience to ocean acidification and ocean warming. 2024. Ohio State University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=osu1721126280854349.

    MLA Style (8th edition)

  • Hulver, Ann. "Heterotrophy promotes coral resilience to ocean acidification and ocean warming." Doctoral dissertation, Ohio State University, 2024. http://rave.ohiolink.edu/etdc/view?acc_num=osu1721126280854349

    Chicago Manual of Style (17th edition)

osu1721126280854349
© 2024, some rights reserved.Creative Commons License Heterotrophy promotes coral resilience to ocean acidification and ocean warming by Ann Marie Hulver is licensed under a Creative Commons Attribution-NonCommercial-NoDerivs 3.0 Unported License. Based on a work at etd.ohiolink.edu.
This open access ETD is published by The Ohio State University and OhioLINK.