Certain species of corals do not require as much sunlight as others to survive. The zooxanthellae that augment nutrient supply to the polyps do rely on photosynthesis, but some species are adapted to less direct sun sources. For example, there are corals within the mesophotic zone of the oceans where solar radiation is low compared to that of a tidepool (even if it rarely receives direct sunlight). For your specific question, the corals likely receive enough sunlight to meet their energetic demand of symbiotic zooxanthellae to complement their predation feeding strategy.