MEPS 362:99-107 (2008)  -  DOI: https://doi.org/10.3354/meps07439

ABSTRACT: Corals have been shown to bleach through the combined effects of elevated sea temperature and high solar radiation. In this study, cores from the west and east sides of a hemispherical shallow reef coral, Goniastrea aspera, were exposed to ambient and elevated water temperature treatments, combined with varying natural solar radiation regimes for periods of 3 d at different times of the year. At elevated temperature, the loss of zooxanthellae from east-side cores was directly related to the dose of solar radiation (measured as photosynthetically active radiation [PAR], 400 to 700 nm). Elevated temperature (+4°C) was responsible for 35% of the total loss, and PAR dose for up to a further 14%. Zooxanthellae from cores from both the east and west sides exhibited chronic photoinhibition (a reduction in maximal photochemical yield [F_v/F_m]) in both the ambient and elevated temperature treatments, which was directly related to the PAR dose. The chronic photoinhibition was consistently greater in the elevated temperature treatment, and also in the east cores relative to the west. These results quantify the direct contribution of solar radiation to both chronic photoinhibition and loss of zooxanthellae. The differences in both loss of zooxanthellae and photoinhibition between the different faces of the coral colony can be directly attributed to differences in prior experience, whereby the west sides of the coral had been exposed to higher natural solar radiation throughout the year, thus conferring greater tolerance to the effects of elevated temperature and solar radiation.

KEY WORDS: Solar radiation · Bleaching · Corals · PAR · Zooxanthellae · Photoinhibition · Photoprotection