Grantee Research Project Results
2001 Progress Report: CISNet: Coral Bleaching, UV Effects, and Multiple Stressors in the Florida Keys
EPA Grant Number: R826939Title: CISNet: Coral Bleaching, UV Effects, and Multiple Stressors in the Florida Keys
Investigators: Anderson, Susan L. , Cherr, Gary N. , Hansen, Lara , Zepp, Richard
Current Investigators: Anderson, Susan L. , Zepp, Richard , Hansen, Lara , Cherr, Gary N. , Oliver, Leah , Jackson, Susan , Brown, Heather , Machula, Jana
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, 2000 through September 30, 2001
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
Objective:
The goal of this project is to evaluate the role that climate change may play in altering the penetration of ultraviolet (UV) radiation over coral reefs and potentially contributing to coral bleaching. This entails examination of both UV-specific stresses upon corals and 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, including laboratory and field assessments of photoprotective pigment concentrations. Our third objective is to further examine the relationships between temperature, UV, and coral bleaching in controlled experiments. Our fourth objective is to measure underwater solar UV irradiance and attenuation coefficients, and 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:
This year, we developed a second, more powerful, technique for evaluating thymine dimers in coral and zooxanthellae. The technique is a 96-well enzyme linked immunosorbent assay (ELISA)-type assay which utilizes a plate reader capable of detecting UV, fluorescence, and luminescence. Using this instrument, with UV-transparent plates, we can determine the DNA concentration in 96 samples in minutes. We attach known amounts of DNA to microplates and perform an immunoassay with chemiluminescent substrate that is quantified directly by the plate reader. Not only does this relieve us from the dot blot procedure, but it eliminates the image analysis step (i.e., having to scan and quantify the developed membrane or X-ray film that results from a dot blot). The plate reader completes this, quantifying each sample in relative luminescence units. We also have a scanner capable of visualizing chemiluminescence in a 96-well plate to generate a visual confirmation of the plate reader results.
We finalized methods for immunolocalization of thymine dimers in coral tissue. This aspect of our work is essential for estimating the proportion of the thymine dimers that are in the coral as opposed to the zooxanthellae tissue; hence, this analysis will help us to interpret our data because the number of zooxanthellae per coral polyp changes during bleaching events. To correct for high levels of autofluorescence observed in Porites porites tissue and zooxanthellae at all wavelengths, we have worked out a method of image subtraction leaving only fluorescence given from thymine dimer labeling. The results of these analyses show that control zooxanthellae have dimers in less than 20 percent of the cells while the 2-hour exposure samples show dimers in 65 percent of the cells with decreased levels seen in the 4- and 6-hour exposures at 30 and 40 percent, respectively. This nonlinear response was also observed in dot-blot analyses for unknown reasons. This could relate to either DNA repair or pigment protection. Analyses will reveal the proportion of dimers in zooxanthellae as opposed to coral tissues.
Last year, we reported that several field and laboratory experiments had been conducted to address the relationship between thymine dimers and coral bleaching. We have delayed the analysis of all samples until the more advanced methods described above were complete. This month, we are completing thymine dimer analyses in approximately 100 coral samples from the field.
One of the major research activities for the 2001 field season was to complete a study of UV and temperature interactions. In July 2001, P. porites samples from Maryland shoals were collected and exposed at Mote Marine Laboratory to +/- UV radiation at two temperatures: ambient and +2°C (visible irradiance was held constant). Levels of UV radiation and visible irradiance were measured hourly, as were temperature and salinity. Corals exposed to UV radiation in the high temperature treatment showed altered behavior during the first few days of the experiment, with some pieces showing bleaching and polyp retraction. Weather may have compromised the experiment in that clouds from a major tropical storm obscured the UV radiation during the last portion of the experiment. Following 8 days of exposure, the experiment was terminated and coral pieces were frozen for pigment and thymine dimer analyses.
During 2001, research continued on factors that affect UV exposure of coral assemblages in the Florida Keys. The location of the sites used for these studies was shown on a map that was provided in our 2000 report. These activities included: (1) measurements of underwater solar UV radiation and optical properties of water samples at various sites located in the Lower Keys; (2) development of algorithms that describe the penetration of UV radiation into the Florida Keys; (3) use of fluorometers for the measurement of UV-protective CDOM at the SEAKEYS CMAN towers located at Sombrero Tower (near Marathon, FL) sites; (4) comparisons of fluoresence and UV attenuation along transects from land out to the coral reefs; (5) research on thermal stratification effects on UV penetration; (6) initial studies in the field and under controlled conditions on UV attenuation by CDOM derived from Florida Bay sea grasses and mangroves; and (7) experiments on the rates of UV absorbance loss of water samples collected near the coral reefs when they were exposed to simulated solar radiation.
Ultraviolet measurement profiles of downwelling and upwelling irradiance at 305, 325, 340, 380, 412, 443, and 555 nm for the water column were obtained using a Satlantic OCP-100 free-falling instrument. Our 2001 studies provided additional data confirming our 2000 findings that the depth dependence of the UV irradiance could be described by an exponential equation, except in stratified waters:
E(,z) = E(
,0) e-Kd(
)z
where Kd() is the diffuse attenuation coefficient of the water at wavelength
. Kd(
) was determined by exponential fits to the irradiance versus depth profiles.
The diffuse attenuation coefficients for the UV region (290-400 nm) correlated
closely with absorption coefficients measured for the colored dissolved organic
matter in filtered (0.2 µm) water samples that were collected at the same time
that the profiles were measured.
The sites for the UV measurements were located close to the coral reefs at Looe Key, Sombrero Tower, and along east-west and north-south transects in Hawk Channel, the region between land and the coral reefs in the Lower Keys. Water samples were collected at the sites, and absorption spectra were obtained after filtration. The UV measurements were accompanied in some trips by concurrent measurements of CDOM fluorescence along the transects. The diffuse attenuation coefficients correlated closely (r2 > 0.9 ) with the fluorescence measurements, providing additional support to our previous finding that CDOM is the major determinant of UV penetration in the Lower Keys region. Other results showed that the highest UV attenuation and fluorescence is located in Hawk Channnel near the Seven Mile Bridge. Major amounts of UV-absorbing CDOM are transported from Florida Bay into Hawk Channel and the Lower Keys region under the bridge.
During 2001, we obtained additional evidence that stratification is having important effects on the penetration of UV radiation into the ocean waters near the coral reefs. Our research in 1999 and 2000 provided initial evidence of this effect near Sand Key, Eastern Sambo, and Maryland shoals. We conducted more detailed studies of this effect at a deep bluewater site (UM215) just south of Looe Key. The UM215 site was selected because depth profiles of its chemical and biological properties are being obtained by a team of scientists from the University of Miami's Rosenstiel School of Marine and Atmospheric Sciences. We also obtained data indicating that the UV penetration at a site adjacent to Looe Key was almost the same during these summer conditions as the surface waters at the site UM215, indicating that the prevailing southeasterly winds push the surface waters up over the reefs. Stratification at the UM215 site was indicated by the sharp drop in water temperature between 30 m and 40 m, a region called the thermocline. Above 30 m, the irradiance decreases exponentially. However, for all wavelengths that are affected by CDOM absorption (290-450 nm), we observed a significant increase in the slope of log plots of irradiance versus depth at the location of the thermocline. This increase indicated that the UV penetration into the water was considerably reduced at the thermocline. To confirm this observation, we collected water samples near the surface and at a depth of 50 m (below the thermocline) and found that the latter samples absorbed UV radiation considerably more strongly than those collected near the surface.
We conducted model simulation using the optical properties of the waters above and below the thermocline. This indicated that, at a depth of 4 m (the average depth of the coral reefs at Looe Key) UV-B exposure is approximately eight times greater with water having the UV attenuating properties of the surface waters at UM215 than it would be if the water having the properities of the deeper water were over the reefs. We attribute the higher clarity of the surface waters to UV-induced photobleaching of the surface waters which increases UV penetration into the surface waters during periods of stratification during the summer. This photobleaching effect was demonstrated by observing decreases in UV absorbance of water samples that were exposed to simulated and natural sunlight under controlled conditions at the Mote Marine Laboratory.
We also conducted initial research on the production of CDOM through decomposition of seagrass litter from close to Looe Key. The grass litter was enclosed by plexiglass chambers at this site and we periodically removed water samples from the chambers. The water samples were analyzed on return to the laboratory. We also conducted studies at the laboratory in which we measured both the buildup in UV absorbance and fluorescence in water containing freshly collected grass litter. These studies were conducted in raceways that contained water collected from Hawk Channel. Results under these controlled conditions indicated that the increase in UV absorbance and fluorescence occurred at approximately the same rate.
Future Activities:
Next month, we will begin extracting additional samples and plan to have all data analyses completed in time for the final project review on September 4-5, 2002. The USEPA Gulf Ecology Division is responsible for the pigment, mycosporine amino acids (MAAs), and tissue protein analyses as well as enumeration of zooxanthellae and polyps. Investigators are completing work on the field samples and will examine newly extracted materials as they become available.
Journal Articles on this Report : 2 Displayed | Download in RIS Format
Other project views: | All 25 publications | 6 publications in selected types | All 6 journal articles |
---|
Type | Citation | ||
---|---|---|---|
|
Anderson S, Zepp R, Machula J, Santavy D, Hansen L, Mueller E. Indicators of UV exposure in corals and their relevance to global climate change and coral bleaching. Human and Ecological Risk Assessment 2001;7(5):1271-1282. |
R826939 (2000) R826939 (2001) R826939 (Final) |
not available |
|
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, ecological exposure, anthropogenic stress, environmental monitoring, UV effects, biomarkers, stressors, thermal stratification, coral bleaching, natural stressors, climate, coastal zone, remote sensing data, Florida Keys, multiple stressors, CISNet Program, ecosystem indicators, biomonitoring, water quality, chromophoric dissolved organic matter, photobleaching, thymine dimers, Florida, FLAProgress and Final Reports:
Original AbstractThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.