The Effects of ultraviolet radiation on skeletal growth and bleaching in four species of Hawaiian corals

Abstract

Coral bleaching has been attributed to many factors, including increased exposure to ultraviolet radiation (UV). The effects of partial and full spectrum UV on coral skeletal growth and bleaching were investigated. Responses were species-specific and depthdependent. Montipora verrucosa, Pocillopora damicornis, and P. danai collected from 1 m maintained or increased their calcification rates when exposed to partial UV or shielded from UV. M. verrucosa collected from 1.5 mexhibited bleaching via zooxanthella loss regardless of the UV treatment, probably because of reduced salinity and water temperature. M. verrucosa collected from 8.5 m bleached only when exposed to increased intensities of PAR, while Porites compressa collected from 8.5 m bleached only when exposed to increases in both PAR and UV. All bleaching resulted from loss of zooxanthellae rather than loss of pigment from zooxanthellae. Lower surface augmentation of color via zooxanthella increases often occurred with a corresponding decrease in upper surface zooxanthella density.