Complex sentence: A coral that has expelled its zooxanthellae may be recolonised by another species perhaps more suited to the stressors present in the environment, however there is a risk that the coral will die before this can occur.
Split into simpler sentences: A coral that has expelled its zooxanthellae may be recolonised by another species that is better adapted to the stressors present in the environment. However there is a risk that the coral will die before that can occur.