TEMPERATURE AND UV EFFECTS ON PIGMENTS IN THE ZOOXANTHELLAE OF AIPTASIA PALLIDA

By Erin Macri and Steve McKagan under the advisement of Suzanne Strom
Western Washington University, Shannon Point Marine Center, SEARUN program

SEARUN
In the summer of 1997 a series of experiments was conducted on the tropical sea anemone Aiptasia pallida as part of the three year Science Education and Research for UNdergraduates (SEARUN) program.  The program is investigating the response of tropical marine symbioses to environmental stresses.  The 1997 research team tested the hypothesis that the disruption of the relationship between zooxanthellae and the host anemone results from increased ultraviolet radiation (UV) and elevated temperatures.  The research included testing of zooxanthellae within the anemone (AZ) and those expelled by the anemone (EZ).  The research focused on three aspects of the bleaching process:

  1. Changes in animal-algal biomass parameters and photosynthetic performance of zooxanthellae.
  2. Changes in the photosynthetic pigments of the zooxanthellae.
  3. Changes in the optical spectra of symbiotic associations during bleaching.
Three main experiments were performed to investigate these parameters in regard to environmental stresses.  The general layout for each is outlined below:
 
Experiment ID 
UVB Dose (J/m2/day)
 Temperature (° C) 
-UVB 0 31
+UVB 89,683 30
Recovery +UVB *89,683/0 *31/27 
Recovery - UVB  *0/0  *31/27 
                         *treatment /recovery
 

INTRODUCTION
Elevated temperatures and UVB have been shown to cause changes in the pigment content and composition of zooxanthellae (Kleppel, 1989 and Lesser, 1996). Loss of pigment , or bleaching, can occur in two main ways: by loss of pigment from cells in the host ,or by reduction of cell denisity within the anemone.  These changes reflect the health of the zooxanthellae, can influence photosynthetic performance and can be combined with spectral data to create diagnostic fingerprints for the health of entire reef systems.

Our 1997 experiments focused on the major zooxanthellar pigments: chlorophyll a, chlorophyll c, and carotenoids (including peridinin,diadinoxanthin,and ß-carotene) and how their absolute and relative cellular concentrations changed in response to elevated UVB and temperatures.

HYPOTHESIS:  UVB and temperature stresses will reduce pigment content of zooxanthellae both within and expelled from the sea anemone Aiptasia pallida.
 

Zooxanthellea isolated from Aiptasia pallida. Photo by Gisele Muller-Parker. Aiptasia pallida with zooxanthellae. Photo by Gisele Muller-Parker.
 METHODS
  • Anemones were exposed to different UVB and temperature regimes in a temperature and light controlled incubator set on a 12:12 L:D photoperiod.
  • Zooxanthellae within the anemone (AZ) and those expelled by the anemone (EZ) were isolated and their pigments were extracted in acetone.
  • Pigments were separated quantitatively by High Performance Liquid Chromatography (HPLC).
    • RESULTS
    Anemones exposed to  30°C (Figure 1)
    • AZ cells showed no large changes in pigment/cell over time
    • EZ cells showed an increase in pigment/cell between 48 and 96 hours
    • EZ cells had a higher carotenoid to chlorophyll ratio which increased over time
    Anemones exposed to 30°C and UVB (Figure 2)
    • AZ cells showed no large change in pigment/cell over timee
    • EZ cells showed no large change in pigment/cell over time
    • EZ cells had a higher carotenoid to chlorophyll ratio which increased over time
    Anemones exposed to 48hrs of 31°C and allowed to recover (Figure 3)
    • AZ cells decreased in pigment/cell during recovery
    • EZ cells increased in pigment/cell during recovery
    • EZ cells had a higher carotenoid to chlorophyll ratio which increased over time
    Anemones exposed to 48hrs of 31°C and 24 hrs of  UVB and allowed to recover (Figure 4)
    • AZ cells decreased in pigment/cell during recovery
    • EZ cells increased in pigment/cell during recovery
    • EZ cells had a higher carotenoid to chlorophyll ratio which increased over time


    SUMMARY
    Visual bleaching was not seen in anemones immediately after treatment, but when given time to recover bleaching was visually evident.  Pigment data confirm these observations:  EZ cells lost Carotenoidto chlorophyll ratios are higher in EZ  than in AZ cells.  This suggests  that AZ and EZ cells have different pigment  compositions.

    CONCLUSION:  UVB and temperature stresses did not alter pigment/cell of zooxanthellae within and expelled from Aiptasia pallida.  However, substantial changes in pigment content occurred during recovery from stress.

    ACKNOWLEDGMENTS
    The authors would like to thank the National Science Foundation (grant RUI-9751047) for funding,  PIs Gisele Muller-Parker, Suzanne Strom, and Jack Hardy, the staff at Shannon Point Marine Center, Gabrielle Mowlds, Kelley Bright, and Clay Cook for providing us with anemones.

    REFERENCES
    Kleppel, G.S., R.E. Dodge, and C.J. Reese. 1989. Changes in pigmentation associated with the bleaching
    of stony corals. Limnol. Oceanogr.  34:1331-1335.

    Lesser, M.P..  1996. Elevated temperatures and ultraviolet radiation cause oxidative stress and inhibit photosynthesis in symbiotic dinoflagellates.  Limnol. Oceanogr.  41:271-283.
     
     


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