EFFECTS OF AMBIENT LEVELS OF SOLAR ULTRAVIOLET-RADIATION ON ZOOXANTHELLAE AND PHOTOSYNTHESIS OF THE REEF CORAL MONTIPORA-VERRUCOSA

Paired flat plates of the hermatypic coral Montipora verrucosa from Ka neohe Bay, Oahu, Hawaii, were acclimated to photosynthetically active radiation (PAR) only and to full sunlight (PAR + UV) for several weeks in the summer of 1990. After the acclimation period, photosynthesis, both in PAR-only and PAR + UV as well as dark respiration were measure d. Levels of the UV-absorbing compounds, ''S320'', density of zooxanth ellae, and chlorophyll a concentration were determined. Corals acclima ted in PAR + UV had higher levels of the UV-protective compounds and l ower areal zooxanthellae densities than corals acclimated in PAR-only. Chlorophyll a per unit volume of coral host and per algal cell did no t differ between corals from the two acclimation treatments. Corals ac climated to PAR + UV displayed higher photosynthesis in full sunlight than corals acclimated to PAR-only, but when photosynthesis was measur ed in the light regime to which the corals had been acclimated, there were no differences in photosynthesis. Dark respiration was the same f or corals from the two acclimation treatments regardless of the light quality immediately preceding the dark period.