The ecology of corals is widely studied as to their role in reef building and because they are good indicators of climate and latitude.  This holds true for paleo-environments as well as environmental forecasting.  All corals require the movement of water for nutrient delivery and waste removal. They do not tolerate large amounts of sedimentation since this tends to clog up their simplified digestion cavity.  Because of their endosymbionts, corals are restricted to clear, shallow waters that are included in the photic zone.  They are most productive at temperatures that range from 25 to 290C.  the rate of metabolism is accelerated by the presence of zooxanthellae because they absorb the waste from the corals and are nutrient sources in nutrient poor zones.  The zooxanthellae also help the corals excrete their calcitic exoskeleton because they produce by-products of photosynthesis that increases the nucleation rate of calcite crystals.  the zooxanthellae can also smother the corals of their grow is very profuse.  One of the corals many predators are Parrot fish that have hard beaks that can crunch the hard corals.  a sudden explosion of the Crown-of-Thorn star fish (picture above) can also be detrimental to corals. Such was the case of large tracks of the Great Barrier Reef  that were destroyed by the organism.  Others include :