The health of coral reefs depend on several factors. one is clean water. erosion on land causes rivers to dump mud on reefs, smothering and killing corals. seawater with too many nutrients speeds up the growth of seaweeds and increases the food for predators of corals when they are developing as larvae in the plankton. coral bleaching occurs when coral polyps lose their symbiotic algae. without the algae, the living coral tissues are nearly transparent, and you can see right through to the stony skeleton, which is white, hence the name coral bleaching. many stressors cause coral bleaching: water that is too cold or too hot, too much or too little light, or the dilution of seawater by the input of lots of fresh water. the #1 cause of bleaching today is the rising temperatures caused by global warming. temperatures more than 2 degrees f (or 1 degree c) above the normal seasonal maximimum can cause bleaching. question: fish play an important role in coral reef health as well. all but one effect listed below is the result of the fish populations within the coral reef.
a)
fish eat predators, such as starfish.

b)
fish eat seaweed and kelp that could potentially smother the coral.

c)
some fish live symbiotically with coral, luring in prey for the coral to kill and eat.

d)
when corals are babies floating in the plankton, fish swim with them and protect them from harm.