1999 Progress Report: CISNet: Coral Bleaching, UV Effects, and Multiple Stressors in the Florida Keys

EPA Grant Number: R826939
Title: CISNet: Coral Bleaching, UV Effects, and Multiple Stressors in the Florida Keys
Investigators: Anderson, Susan L. , Santavy, Debbie , Hansen, Lara , Zepp, Richard
Current Investigators: Anderson, Susan L. , Cherr, Gary N. , Brown, Heather , Machula, Jana , Hansen, Lara , Oliver, Leah , Zepp, Richard , Jackson, Susan
Institution: University of California - Davis
Current Institution: University of California - Davis , U. S. Environmental Protection Agency
EPA Project Officer: Packard, Benjamin H
Project Period: October 1, 1998 through September 30, 2001
Project Period Covered by this Report: October 1, 1998 through September 30, 1999
Project Amount: $407,567
RFA: Ecological Effects of Environmental Stressors Using Coastal Intensive Sites (1998) RFA Text |  Recipients Lists
Research Category: Environmental Statistics , Aquatic Ecosystems , Ecological Indicators/Assessment/Restoration


The overarching goal of this project is to evaluate the role that climate change may play in altering penetrance of ultraviolet (UV) radiation over coral reefs and potentially contributing to coral bleaching. This entails examining UV-specific stresses upon corals, together with factors that influence UV penetrance over the reefs. Our first objective is to develop immunofluorescence techniques to examine UV-specific lesions in DNA (thymine dimers) of coral and zooxanthellae. Our second objective is to determine whether UV-induced DNA damage and indices of coral bleaching are correlated. Our third objective is to develop a monitoring study of temperature and UV effects at selected sites in the Florida Keys, and the fourth objective is to further examine the relationships among temperature, UV, and coral bleaching in controlled experiments. A separate, but highly integrated, component of the project seeks to measure underwater solar UV irradiance and attenuation coefficients, as well as to develop continuous observations of chromophoric dissolved organic matter (CDOM) concentrations and algorithms that relate CDOM concentrations to UV exposure of coral assemblages.

Progress Summary:

Dr. Anderson and coworkers at the Bodega Marine Laboratory have developed an immunoblottting assay using DNA from the coral Porites porites. Method development for the thymine dimer immunoblotting assay included optimization of various procedures such as DNA extractions, blotting methods, and quantitation. They observed dose-dependent increases in thymine dimers following irradiation of coral DNA in the laboratory. They also have developed a laboratory standard using purified salmon DNA irradiated in a UV crosslinker. In addition, the assay was used to determine whether thymine dimers are detected under realistic field exposure conditions. Five pieces of P. porites were collected at Maryland Shoals (the collection site in the mid-Florida Keys near the Summerland Key Mote Marine Laboratory, July 30, 1999) at 0830 hr and five were collected at 1300 hr to represent "low" and "high" light exposures. As expected, "low light" samples exhibit lower levels of thymine dimers than do coral samples collected under "high light" conditions, indicating that differences in levels of thymine dimers can be detected under realistic exposure conditions.

As an additional step in method development for the immunoblotting procedure, a dose-response experiment was conducted using a solar simulator. P. porites were irradiated in a Suntest solar simulator. An increase with dose was observed, although effects were not strictly proportional at the lowest exposure times. This could be a result of a variety of methodologic issues, which are now under investigation, and/or DNA repair in the coral at low doses. These findings are encouraging and indicate both that methods are appropriate and that increases in UV irradiance can be discerned.

Next, they questioned how thymine dimers vary diurnally and whether effects are cumulative from day to day. P. porites were transplanted onto plastic plates fixed to a PVC rack at the experimental site at Eastern Sambo Reef. Coral were exposed using three light treatments (UV-opaque, UV-A + PAR, and UV-transparent). Four replicate samples were removed at 0830 hr, 1300 hr, and 1800 hr for 2 days and at 0830 hr and 1300 hr on the third day. The coral were split, and half of each coral sample was preserved for thymine dimer assays at the Bodega Marine Laboratory. The other half was preserved for analysis of chlorophyll content, tissue protein, and zooxanthellae counts at the U.S. Environmental Protection Agency (USEPA) Gulf Ecology Division. These analyses are currently underway. Finally, BML investigators are developing cellular localization procedures using immunofluorescence techniques that will allow them to determine where dimers are localized within coral tissue as well as zooxanthellae.

UV measurements were made as part of the experiments conducted during July at Eastern Sambo and nearby sites. The base for these experiments was the Summerland Key Mote Marine Laboratory, where various spectroscopic instruments and a solar simulator transported from the Athens EPA laboratory were located. The measurements, including downwelling and upwelling vertical profiles of UV and visible radiation, were obtained using a Satlantic OCP-100 free-falling instrument. Profiling was conducted at high and low tide along transects, which included a series of sites ranging from deep water outside the reefs ranging across Hawk Channel into sites located close to land. Water samples were concurrently obtained at these sites, and absorption and fluorescence spectra of the filtered water samples were obtained at the Summerland Key laboratory. Profiling and water sampling also were conducted at Sand Key near a SeaKeys CMAN tower site where we plan to locate fluorometers for continuous measurements of UV-absorbing organic matter in the water.

Investigators also estimated spectral diffuse attenuation coefficients that describe the penetration of solar UV radiation into the seawater at the Eastern Sambo reef and nearby sites. These estimated values were in good agreement with measured values. They used the TUV model of Madronich et al. and TOMS satellite observations of total ozone over the Florida Keys and South Florida to estimate solar spectral irradiance at these sites and, for comparison, at the EPA UV monitoring site located in the Everglades. These simulated values for the Everglades were very close to measured values at this site. Diffuse attenuation coefficients and surface irradiance values were used to estimate underwater UV irradiance in the Eastern Sambo area. Using the Setlow action spectrum for DNA damage, weighted irradiance values and dose rates of damaging UV were computed for various depths. Results of these analyses indicate that the coral reefs at Eastern Sambo were receiving considerable exposure to UV-B radiation during July that was approximately 25-35 percent of surface UV irradiance at a depth of 3-4 m. However, the water just inside the reef in Hawk Channel and closer to land was considerably more opaque to UV due to the presence of higher concentrations of UV-absorbing colored dissolved organic matter (CDOM) derived from sea grasses, from on-shore mangroves, and possibly from long-range transport of DOM from the Gulf north of the Florida Keys. Experiments at the Summerland Key Mote Marine Laboratory indicated that water from Hawk Channel photobleached with loss of UV absorbance and fluorescence when it was exposed to simulated solar radiation. These results indicate that interactions between photobleaching of the DOM and transport of near-shore water out over the reefs may play a key role in controlling UV penetration to the reef surface.

Future Activities:

The main objective for next year will be to transplant coral from 5 m depth to 1, 3, and 5 m to determine how increased UV would affect the coral and zooxanthellae, and to evaluate whether thymine dimers and indicators of coral bleaching are correlated. This experiment will simulate the effects of transient increases in UV penetrance and will build on data from the diurnal experiments conducted last year. Preliminary experiments also will begin to examine relationships among temperature, UV, and coral bleaching. Investigators also will more carefully examine the effects of water stratification and photobleaching on UV exposure at the corals sites, conduct manipulations to elucidate factors that affect the photobleaching, assist with experiments to determine action spectra for DNA damage in selected coral samples, obtain continuous data on CDOM concentrations at the Sand Key site based on fluorescence measurements, and continue to develop methods to relate the Keys spectral data to the Everglades ground observations of UV spectral irradiance, and the SeaWiFS and TOMS data sets for the Keys region.

Journal Articles on this Report : 1 Displayed | Download in RIS Format

Other project views: All 25 publications 6 publications in selected types All 6 journal articles
Type Citation Project Document Sources
Journal Article Stabenau E, Zepp RG, Bartels E, Zika RG. Role of seagrass (Thalassia Testudinum) as a source of chromophoric dissolved organic matter in Coastal South Florida. Marine Ecology-Progress Series 2004;282:59-72. R826939 (1999)
R826939 (2000)
R826939 (2001)
R826939 (Final)
not available

Supplemental Keywords:

global climate, stratospheric ozone, marine, ecological effects, ecosystem indicators, aquatic, ecology, zoology, genetics, remote sensing, Atlantic Coast, Gulf Coast, southeast., RFA, Scientific Discipline, Air, Geographic Area, Ecosystem Protection/Environmental Exposure & Risk, Ecology, Ecosystem/Assessment/Indicators, Ecosystem Protection, Chemistry, climate change, State, Monitoring/Modeling, Ecological Effects - Environmental Exposure & Risk, Ecological Risk Assessment, Ecological Indicators, anthropogenic stresses, ecological effects, environmental monitoring, anthropogenic stress, ecological exposure, biomarkers, stressors, UV effects, thermal stratification, coral bleaching, Florida Keys, remote sensing data, coastal zone, climate, natural stressors, multiple stressors, CISNet Program, biomonitoring, ecosystem indicators, water quality, chromophoric dissolved organic matter, Florida, photobleaching, thymine dimers, Global Climate Change

Relevant Websites:

UC Davis Bodega Marine Laboratory Web Site

Progress and Final Reports:

Original Abstract
  • 2000 Progress Report
  • Final Report