Term of Award

Spring 2003

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

Stephen P. Vives

Committee Member 2

Sophie George

Abstract

Coral reefs occur at low latitudes in clear, nutrient poor waters where high intensities of ultraviolet radiation (UVR, 280-400 nm) exist. Several negative effects of UVR have been demonstrated on adult corals, such as reduced calcification and skeletal growth rates, damage to tissue, and disruption ofphotosynthesis in symbiotic algae. In addition, high UVR in conjunction with increased water temperatures has been linked to coral bleaching. Adult corals have evolved to deal with UVR stress by producing compounds called mycosporine-like amino acids (MAAs) that absorb biologically harmful wavelengths ofUVR between 309 and 360 nm. Organisms that incorporate a suite of MAAs with a range ofabsorbance maxima create a broadband filter that protects them from UVR damage without blocking the necessary photosynthetically active radiation (400-700 nm) need by the symbiotic zooxanthellae in the coral animal.

Detrimental effects ofUVR have also been found in coral larvae such as reduced settlement, survival, and lower chlorophyll concentrations. Previous studies indicate that UVR may play a role in survival during dispersal of coral larvae, but its effects on newly settled coral recruits have not previously been investigated. The purpose ofthis study was to determine if exposure to biologically relevant UVR has a negative impact on newly settled coral recruits. This objective was obtained by addressing several specific questions. First, does UVR exposure affect the health of newly settled coral recruits as measured by survival, growth, chlorophyll concentrations, and protein levels? Second, if UVR exposure is sub-lethal, do recruits alter concentrations ofMAAs to counter the negative effects of this radiation?

Experiments investigating UVR effects on coral recruits were conducted at Mote Marine Laboratory, Summerland Key, Florida. Twenty adult colonies of the green color morph of Porites astreoides were collected from West end of Bahia Honda and the West end of 7-mile bridge and subsequently held in flow-through tanks for one year under 80% shade cloth. One year later larvae were collected from these colonies between 4 April to 20 June, 2002, and settled onto small pieces of coral rubble. Pieces of coral rubble with attached recruits were randomly divided between two experimental tanks, and placed under one of three light treatments: PAR+UVA+UVB (280-700 nm), PAR+UVA (320- 700 nm), and PAR (400-700 nm).

Health of P. astreoides recruits; measured as survival, change in size, total chlorophyll concentrations and protein levels, was not affected by biologically relevant intensities of UVR. HPLC analysis revealed the following types of MAAs in recruits: mycosporine-glycine ( λmax = 310 nm), palythine ( λmax = 320 nm), asterina ( λmax= 330 nm), shinorine ( λmax = 334 nm) and porphyra ( λmax = 334 nm). After twenty days, recruits under the PAR+UVA+UVB light treatment had significantly higher concentrations of shinorine ( λmax =334 nm), porphyra ( λmax = 334 nm), and asterina ( λmax = 330 nm) than the PAR+UVA and PAR light treatments. The peak absorbance ofthese three amino acids coincides with the peak spectrophotometric scan absorbance at 331 nm. Interestingly, mycosporine-glycine was found in the highest concentration of all the MAAs, but the concentration did not differ significantly between light treatments. This could possibly be explained by the fact that larvae were originally released with high concentrations of mycosporine-glycine. It could also be due to the high total dose of UVB received. Thus, UVR exposure induces changes in the concentration of MAAs in settled recruits of P. astreoides in a short period of time, but does not affect their health.

Copyright

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