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.
| Identifer | oai:union.ndltd.org:nova.edu/oai:nsuworks.nova.edu:occ_stuetd-1120 |
| Date | 01 January 2005 |
| Creators | Foster, John Gregory |
| Publisher | NSUWorks |
| Source Sets | Nova Southeastern University |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | Theses and Dissertations |
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