All ETDs from UAB

Advisory Committee Chair

Dustin W Kemp

Advisory Committee Members

Charles D Amsler

Andrea G Grottoli

Stacy A Krueger-Hadfield

James B Mcclintock

Document Type

Dissertation

Date of Award

2023

Degree Name by School

Doctor of Philosophy (PhD) College of Arts and Sciences

Abstract

Despite coral reefs declining globally, thermally resilient coral-dinoflagellate communities have been identified, providing insight into how corals can inhabit warmer environments. These corals are able to better resist and recover from thermal stress events compared to adjacent, offshore conspecifics that are found in habitats that have cooler temperatures. To better understand the physiological traits that make corals resilient, I measured the initial tissue biomass and energy reserves of eight coral species. These corals were collected from both warm-water nearshore habitats and offshore reefs with milder temperatures in Palau, Micronesia. Despite contrasting environments, coral tissue similarities between these populations were striking, revealing that symbioses with resilient dinoflagellates and relying upon more heterotrophically derived carbon helps mitigate the warmer and more acidic conditions and reduces the colonies physiological stress. We examined tissue biomass and energy reserve catabolism of Pocillopora verrucosa and Psammacora digitata during a 13-day thermal stress experiment, to determine if nearshore and offshore populations utilize energy-dense compounds differently under physiological stress. Our results show limited evidence of differential catabolism and support the important role thermotolerant symbionts and corals’ diet has on resilience. Coral reef ecosystems in the Florida Keys are at an advanced stage of decline compared to reefs in Palau, but similarly nearshore coral are more resilient to marine heatwaves and are declining at slower rates than offshore reefs. Over four years, I investigated symbiotic dinoflagellate community composition, coral holobiont tissue biomass, and energy reserves of Orbicella annularis, O. faveolata, and Porites astreoides, to determine potential causes of this differential decline. Ultimately, nearshore corals have positive legacy effects, which bolster these colonies, by aiding in biomass, total lipid, and wax ester anabolism within a year following physiological stress events, enabling these populations to be better equipped for another stress event. Contrastingly, offshore coral populations were coping with negative legacy effects of still recovering biomass after the 2015 bleaching event, with low lipid and wax ester content. As global temperatures continue to rise at alarming rates, coral reefs will continue to decline, however, all populations are not equally threatened by moderate rises in seawater temperatures. This dissertation provides insight into the specific roles coral hosts and symbionts have in facilitating resistance and recovery to marine heatwaves and ultimately coral reef ecosystem resilience.

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