A recent study suggests that corals with greater diversity of symbiodinium (aka zooxanthellae) are more sensitive to environmental changes than corals with fewer variety of symbiodinium. Published by the Royal Society Biological Sciences, the research breaks down the corals as generalists and specifists, Generalists, like Acropora, are more susceptible to environmental stressors. Conversely, Porites is a specifist and much more resiliant. While the study is more suggestive, it does lend some good discussion.
One could assume that a generalist would be more able to experience fast growth under a range of conditions but also more inclined to bleach, while a specifist may hold onto their one or two endosymbiotic algae through thick and thin. A generalist, like Acropora, might have evolved to ditch the stressed symbiodinium for the assumption of being able to take in a more adaptable algae. But we’re just thinking out loud here. Ecology has always suggested that biodiversity is a key to stability. In this case, a lack of diversity within the corals themselves is a more stable recipe for long term survival.