Graduation Year

2006

Document Type

Thesis

Degree

M.S.

Degree Granting Department

Marine Science

Major Professor

Frank E. Muller-Karger, Ph.D.

Keywords

Sea Surface Temperature (SST), Remote sensing, Ocean color, Coral reef resilience, Coral cover, Coral Reef Evaluation and Monitoring Program (CREMP)

Abstract

I examined the hypothesis that high variability in Sea Surface Temperature (SST) and ocean color are associated with higher coral cover and slower rates of decline of coral cover within the Florida Keys National Marine Sanctuary (FKNMS). Synoptic SST time series maps, covering the period 1994-2005, were constructed for the FKNMS with data collected using the National Oceanic and Atmospheric Administration (NOAA) Advanced Very High Resolution Radiometer (AVHRR) satellite sensors. The SST data were compared with coral cover time series assessments at 36 sites conducted by the Coral Reef and Evaluation Monitoring Program (CREMP; 1996-2005), sponsored by the Environmental Protection Agency and the State of Florida. Out of the 36 stations, Smith Shoals routinely experienced very different and extreme environmental conditions relative to the rest of the stations, including extreme salinity, suspended sediments, and "black water" events that led to the death of coral reef organisms such as in 2002. Among the other 35 stations, sites that experienced moderately higher SST variability (mean variance > 6) relative to other sites showed a trend toward higher percentage coral cover (r=0.62, p=6.33x10-5, N=35) and relatively slower rates of decline (r=0.41, p=0.02, N=35) over the 12-year study period. The results suggest that coral reefs sites that are continuously exposed to high but not extreme variability in temperature may develop resilience against episodes of extreme cold or elevated SST.

Variability of suspended sediments and water clarity were estimated using satellite-derived, normalized water-leaving radiance products. Ocean color data were obtained from the Sea-viewing Wide-Field-of View Sensor (Sea WiFS) from 1998 to 2005. Normalized water-leaving radiance at 443 (Lwn443) was used as a proxy to examine variability in water clarity, and normalized water-leaving radiance at 670 (Lwn670) was used as a proxy to study variability in suspended sediments. A weak relationship was identified between variability of Lwn443 and Lwn670 and coral cover as estimated by CREMP assessments in 2005 (r=0.43, p = 0.01, N=35 and r = 0.47, p = 0.005, N=35, respectively). There was a weak relationship between coral cover change and Lwn670 from 1988 to 2005 (r = 0.46, p = 0.05, N=35), but there no relationship was observed between variability of Lwn443 and change in coral cover (r =0.27, p =0.11, N=35). Further research is required to understand the origin, concentration and composition of dissolved or suspended materials that change the turbidity of waters around reefs of the FKNMS, and whether these changes can be adequately interpreted by examining concurrent satellite imagery. Ultimately, such remote sensing and field research is required to understand how water quality affects the health of coral reefs, and how coral ecosystems adapt to environmental variability.

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