Master's Theses

Date of Award

2015

Document Type

Thesis

Department

Biology

First Advisor

Kyle McDonald

Second Advisor

Ana Carnaval

Keywords

Coral reef, remote sensing, reflectance

Abstract

Around the world, climate change, land-based pollution and fishing impacts are recognized as principal threats to coral reef ecosystems. Sea surface temperatures, in particular, are expected to change dramatically over the next decades and result in high coral mortality in some regions. Through controlled experiments, I examined changes in coral fluorescence and reflectance in response to water temperature alterations to assess the potential of employing these signatures as a diagnostic tool to measure coral health. At the NOAA Coral Culture and Collaborative Research Facility, I conducted controlled laboratory-based heat stress experiments on three Caribbean species of coral: Acropora cervicornis, Orbicella annularis, and Porites furcata. All species exhibited signs of stress and bleaching after the experiment, based on their chlorophyll fluorescence and reflectance responses. Upon exposure to water temperatures raised incrementally from 31C to 34C, no significant change was observed in host fluorescence for A. cervicornis and O. annularis; however, a change was detected for P. furcata. I nonetheless detected change in the algae’s (zooxanthellae) fluorescence in both A. cervicornis and O. annularis. Fluorometer analyses further demonstrated that the photosystems of the algae (PSII) were damaged by exposure to higher water temperatures, implying that the immediate effect of the heat stress was on them, as opposed to the hosts. These results support the use as algae fluorescence as an early indicator of change in coral health. While measurements of host fluorescence were not clear indicators of coral health and bleaching changes in my experiments, the detected changes in reflectance were consistent with declining coral health: due to the larger proportion of exposed skeletal material, stressed corals had higher reflectance values relative to controls. This study will be extended to examine possible linkages with satellite-based remote sensing measures utilized in NOAA’s Coral Reef Watch in an attempt to help managers and 2 conservation agencies to more efficiently monitor and preserve coral health at regional and global scales.

 
 

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