Theses and Dissertations

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Defense Date

2005

Document Type

Thesis - NSU Access Only

Degree Name

M.S. Marine Biology

Second Degree Name

M.S. Coastal Zone Management

Department

Oceanographic Center

First Advisor

Bernhard Riegl

Second Advisor

Richard E. Dodge

Third Advisor

Curtis Burney

Abstract

The effects of a seven-day exposure to a 2°C increase above the maximum summer temperature and an 86% reduction in subsurface irradiance on the net photosynthetic output and mortality of the scleractinian coral species Montastrea cavernosa were examined in vitro as both single- and simultaneous multiple-stressor events. The effect on photosynthetic output was expressed as the percent change in the Pg:R24 ratio following the seven-day treatment period. Mortality was defined as the absence of viable coral tissue at the end of the seven-day recovery period. The level of elevated temperature (31.5°C) was based on partial datasets of in situ measurements of subsurface temperature, spanning the years 2000-2002, recorded on the crest of the outer reef tract of Ft. Lauderdale, FL at a depth of 15m. The degree of irradiance attenuation was equivalent to an increase in turbidity from the ambient value of 0.3 NTU at the average specimen collection depth of 21.3 m to a value 10 NTU, induced by an increase in total suspended solids from 7.6 to 57.0 mg L-1. The individual stressors of elevated temperature and reduced irradiance both produced significant, sub-lethal depressions of the Pg:R24 ratio of M. cavernosa colonies, but a significant interaction between the two stressors was not detected. However, simultaneous exposure to the two stressors did result in significantly greater post-recovery mortality, evidence of an exacerbative interaction between elevated temperature and reduced irradiance for the relatively deep dwelling colonies of M. cavernosa in this study. The finding of a significant exacerbative interaction between elevated temperature and reduced irradiance on coral mortality illustrates the importance of considering multiple-stressors when assessing the effects of anthropogenic and natural disturbances on the current and future health of coral reefs. Pertinent to local issues of coastal zone management, the finding of a significant effect of attenuated radiance on the Pg:R24 ratio and a potentially lethal interaction between attenuated irradiance and elevated temperature indicates the current Florida regulatory limit of 29 NTU above background may not adequately protect scleractinians occupying the deeper reef zones.

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