Algal Symbionts Increase DNA Damage in Coral Planulae Exposed to Sunlight

To test the hypothesis that algal symbionts make coral larvae more susceptible to high photosynthetically active radiation (PAR) and ultraviolet radiation (UVR), symbiotic and non-symbiotic planulae of Acropora tenuis were exposed to natural sunlight (high PAR and UVR) at an ambient temperature of approximately 27°C for 4 d. DNA damage to host cells was detected using a comet assay (single-cell gel electrophoresis). Coral cells from symbiotic planulae had longer comet tails than those from non-symbiotic planulae, indicating that cells in symbiotic larvae had more DNA damage than those in non-symbiotic larvae. This result suggests that symbiotic algae are a source of oxidative stress in larvae under conditions at the ocean surface.