Complex sentence: Ocean water quality and the health of coral species are both symbiotic and reflexive; polluted water negatively impacts the health of coral reefs, and unhealthy reefs add to the degradation of ocean water quality.
Split into simpler sentences: Ocean water quality and the health of coral species are both symbiotic and reflexive. Polluted water conditions negatively impact the health of coral reefs, and unhealthy reefs, in turn, add to the degradation of ocean water quality.