Term of Award

Summer 2001

Degree Name

Master of Science

Document Type and Release Option

Thesis (restricted to Georgia Southern)

Department

Department of Biology

Committee Chair

Daniel F. Gleason

Committee Member 1

Alan W. Harvey

Committee Member 2

James B. Claiborne

Abstract

In this study I used Aiptasia pallida, a common Caribbean anemone as a proxy for anthozoan/algal symbiosis, to investigate 1) the origin of carotenoid pigmentation and the role of carotenoids as ultraviolet radiation (UVR) photoprotectants and 2) the repopulation and photoadaptive response of symbiotic algae (i.e., zooxanthellae) after bleaching. An experiment was conducted to partition the effects of UVA (320 - 400nm), photosynthetically active radiation (PAR; 400-700nm) and host feeding on the pigmentation of bleached and unbleached anemones. This experiment ran for 38 days and bleached and unbleached anemones were exposed to one of three light treatments: high PAR and high UVA; high PAR and low UVA; and low PAR and no UVA.

Carotenoids positively identified in A. pallida by high pressure liquid chromatography (HPLC) included peridinin, diadinoxanthin, diatoxanthin and (3-carotene. In CHAPTER III, I show that including a carotenoid-rich diet of Artemianauplii has no effect on the carotenoid composition of A. pallida. However, a 2-way analysis of variance (ANOVA) reveals that anemones exposed to high UVA had significantly higher diatoxanthin relative to the total xanthophyll pool [diato : (diato + diadino)] during the first 10 days of the experiment. A decrease in xanthophyll cycle activity at 20 days suggests photoadaptation of anemones to high UVA and may coincide with an increase of additional photoprotective measures such as mycosporine-like amino acids. Exogenous feeding also affects the photoprotective abilities of carotenoids as xanthophyll cycling increased in unfed treatments.

In CHAPTER IV, zooxanthella densities and concentrations of pigments per zooxanthella were compared between bleached and unbleached anemones to assess the photoadaptive response of symbiotic algae after bleaching. Cold temperature-induced bleaching of A. pallida increased mean pigments per zooxanthella and photoprotective xanthophyll activity. Increases in pigmentation among bleached anemones may be related to differential bleaching of light-adapted zooxanthellae from the tentacles and oral disk of the anemones, the nutrient status of the symbiosis and/or presence of multiple phylotypes of zooxanthellae. Bleached anemones in high PAR and low and high UVA treatments differed little in the recovery of zooxanthellae density and pigment per zooxanthellae. Low PAR and no UVA treatments, on the other hand, had depressed growth at 10 days and maintained higher pigments per zooxanthella for the remainder of the experiment. The results of this study suggest the UVA has little effect on zooxanthellae repopulation and pigment concentrations per cell after a bleaching event.

Copyright

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