By Dan Bostrom under the advisement of Jack Hardy
Western Washington University, Shannon Point Marine Center, SEARUN Program

INTRODUCTION
The stratospheric ozone layer (11- 15km altitude) protects living organisms from harmful solar ultraviolet radiation (UVR).  Many marine organisms, including corals and anemones, are symbiotic, i.e. they have algal cells that provide the animal with photosynthetic carbon.  Bleaching, the loss of pigments or algal cells, occurs as a response to environmental stress, including increased temperature and/or UVBR.

This project is part of an overall research effort to determine the nature of the bleaching process by exposing the anemone Aiptasia pallida to two known stressors (temperature and ultraviolet radiation) in different experimental treatments. A full understanding of any organismal response requires that the treatment conditions be made as similar as possible to natural radiation.  UVR is broken into three regions based on wavelength: UVA (320 –400nm), UVB (290 – 320nm), and UVC (< 290nm).  UVA is not very harmful, and the atmosphere attenuates UVC.  UVB however, includes wavelengths that are short enough to cause damage and long enough to be only moderately attenuated by the atmosphere.  Furthermore, the intensity reaching the Earth’s surface is affected by fluctuations in the thickness of the ozone layer.

Measurements of artificial and solar lighting are necessary in order to simulate the wavelength-specific energy distribution found in solar radiation. As the damage per unit energy varies with wavelength, it is necessary to convert UVB to what is termed biologically effective UVB by applying a damage weighting function.  The objective of my portion of the project was to quantify all optical spectra used in the experimental exposures.

METHODS
Aiptasia pallida was exposed to UV and elevated temperature in July and August 1997 in a light and temperature controlled incubator.  A bank of three ultraviolet (UV-B 313, Q-Panel Co.) and three full spectrum fluorescent (GE Plein Flow, 48”, 40W, 225 lumens) lamps were used to supply lighting.  A built-in timer regulated the light cycle to a 12hr light:dark photoperiod while a thermostat regulated the temperature at a constant 27.0 degrees Celsius.

Cellulose acetate filters were used to remove UVC radiation created by the UV lamps and mylar filters were used to remove the remaining UVB radiation to a non-harmful level for the control samples.  These filters were incorporated into lids placed directly over the anemone sample dishes (Figure 1). Both filter materials were replaced after each experiment (mylar after every other) to assure that UV degradation of the filters did not affect light attenuation.

A Licor LI-1800 Spectroradiometer was used to measure irradiance at each wavelength from
300 to 800nm for each experimental treatment.  Irradiance data were downloaded to a computer and outliers were removed. Wavelengths below the instrumental range (i.e. 300nm – 290nm) were estimated by best curve fit extrapolation.  UV-B irradiance was converted to biologically-effective dose using two different damage weighting functions (EXP-300 and DNA-300).  EXP-300 yields values relevant to photoinhibition in algal cells and DNA-300 permits comparison of recorded values to other published data.  Integration of irradiance in the UVB range with respect to time gave the energy dose per treatment.

RESULTS
A series of spectra measurements were taken inside the incubator before any experiments were conducted.  Each measure evaluated a different filter combination or position.  These results were used to designate a set of three UVB treatments and an optimum incubator position for four experiments.  The designations reflect the relative UVB intensity.

• –UV          Effectively no UVB (2 layers mylar, 1 cellulose acetate)
• +UV          Some UVB (1 layer cellulose acetate, 1 screen mesh)
• ++UV        Full UVB (1 layer cellulose acetate)

1. Wavelength dependent irradiance: relative intensity per wavelength.
2. Time dependent irradiance: relative intensity per hour
3. Energy dosage: the total energy irradiated over time at the rate described

CONCLUSION
All results compared favorably with the natural solar conditions which the treatments sought to duplicate in the UVB range.  However photosynthetically active radiation was only 2.5% of solar.

ACKNOWLEDGMENTS
The author would like to thank the National Science Foundation (grant DBI-9711075) for funding,  PIs Gisele Muller-Parker, Suzanne Strom, and Jack Hardy, the staff at Shannon Point Marine Center, Gabrielle Mowlds, Kelley Bright, Clay Cook for supplying us with anemones and Charles Mazel for providing us with the Benthic Spectrofluorometer.

REFERENCES
Behrenfeld, M., (1993). Effects of Ultraviolet-B Radiation on Primary Production along Latitudinal Transects in the South Pacific Ocean. Marine Environmental Research, 35, 349-363.

Frederick, J. E., Lubin, D., (1994). Solar Ultraviolet Irradiance at Palmer Station, Antarctica. Antarctic Research Series, 62, 43-52.