There are many different abiotic factors that can affect an ecosystem, including rainfall and temperature. But for coral reefs, one of the biggest factors is water temperature. If the water is too warm of too cold, coral will die. Corals cannot tolerate water temperatures below 18°C. Corals grow optimally in water with temperatures between 23-29°C. Some corals can tolerate water temperatures of 40°C , but only for a short while.