A major threat to the corals of the reef is the acidification of the oceans (p.H level)
Oceans are assumed to of absorbed up to half of the excess amount of CO2 produced by humans in the past two centuries. Roughly around half of the CO2 is located in the higher 10% of the oceans, less than 1000m in depth, due to the slow process of ocean currents, this is where the coral reefs are located. The carbon-dioxide is absorbed into the oceans creating carbonic acid as it bonds with the sea water, this causes the pH level to lower, causing the ocean to be less alkaline. The current pH of our ocean is 8.2, it is predicted that by 2100 the pH of our oceans will be 7.8. The acidity slowly dissolves the calcium-carbonate based skeletons, and shells of marine life, destroying their environment, and habitat.
Global warming, the affects of global warming on the reefs can be catastrophic for the corals. Global warming contributes to ocean acidifcation, and the rising of ocean temperatures. Rising of the ocean's waters stresses out the corals, causing them to expel the zooxanthellae, doing so leaves the coral without their main source of food as the algae contributes 95% of the corals energy. If not recovered, the coral will die. If recovery is able to occur, the coral will remain bleached until doing so.
Human impacts on coral stems from the pollution of ocean waters, oil spills, acid spills, etc, they all change the acidification, temperature, and make up of the ocean, thus, in turn causing the coral to stress, which causes the coral to bleach, with a possibility of death.
A building of the resort on Heron Island could result in a number of issues. These issues include, pollution, noise disruption, and general disturbance. These pollutants stress the corals, their foods, and other prey/predators of the ecosystem. In turn causing death, fleeing, and injury to the ecosystem. All in which lead up to the coral stressing, which causes them to bleach or die.
These impacts on the reef are catastrophic. If the coral bleaches, they won't have a food source in which they can acquire their energy from. Without a food source, the corals won't have enough energy to reproduce with one another. Without the corals reproducing, there won't be any new colonies, and without any new colonies, if the coral dies, the reef will vanish. After vanishing commences, the lime stone skeletons will erode into the ocean, causing the acidity to raise, and to be no places or coral life.