Title

The Effects of Artificial Shading on Coral Bleaching Due to Thermal Stress on the Endangered Coral Species Orbicella faveolata

Graduation Date

5-2017

Document Type

Honors Thesis

Degree Name

Bachelor of Science

Department

Natural Sciences and Mathematics

Director of the Honors Program

Gigi Gokcek, Ph.D.

First Reader

Vania Coelho, Ph.D.

Second Reader

Doreen Gurrola, M.S.

Abstract

Many corals rely on a symbiotic relationship with zooxanthellae to survive. However, under conditions of thermal stress and high light intensity, this symbiosis breaks down and algae are expelled from coral tissues. This process is referred to as coral bleaching. Global climate change is increasing thermal stress on coral reefs around the world, accelerating the rate of such events. This study aimed to investigate the possibility of mitigating effects of cumulative thermal stress on corals by reducing light intensity, through the use of artificial shades. In this laboratory experiment, we studied an endangered Caribbean reef building species, Orbicella faveolata. A total of 259 fragments from 4 coral colonies were divided among 6 aquaria. Each tank contained approximately 43 fragments, with at least 10 from each coral colony. The treatments included 2-80% shaded and 2 non-shaded high temperature tanks maintained at 31.50C , and two non-shaded control tanks at 26.50C. NOAA’s Coral Reef Watch methodology was used to determine cumulative thermal stress, which was defined as Degree Heating Week (DHW). Coral color shade was observed, using the Coral Watch – Coral Health Chart, through pictures taken at the beginning of the experiment and each of the eight DHWs. The controls showed a significant difference in mean coral color shade as compared to the high temperature non-shaded tanks in DHWs 7 and 8. The high temperature 80%shaded treatment had a significantly higher mean coral color shade as compared to the controls and the high temperature non-shaded tanks, starting early in the experiment (DHW 2). The results indicate that a reduction in light intensity was the major factor increasing the mean coral shade of the colonies. Thermal stress was mitigated by shading only at the end of the experiment.

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