Many corals have a mutualistic relationship with a photosynthetic bacteria called zooxanthellae. The bacteria helps the coral obtain an energy source and the coral provides a home for the bacteria. Rising temperatures is causing an issue with the relationship between the bacteria and coral. Rising temperatures also increase the the water levels. This means the barrier reef is not able to perform its main function, which is absorbing most of the energy from the ocean current and protecting the coast line of eastern Australia.
The sea star population is also starting to increase because of the increase in water temperatures. Sea stars are one the main predators to coral, so the population of coral organisms is suffering from predation.
Eco-tourism is a major source of income for the residents of eastern Australia, so when people visit the region one of the major attractions is visiting the Great Barrier Reef. The majority of tourists do not understand how fragile the corals are and just simply touching them can cause death. An increase in visitors to the reef will also cause an increase in trash, which leads to other animal deaths.
The Great Barrier Reef, the world's largest coral reef system, is situated off the coast of northeast Australia.
The problems facing the Great Barrier Reef are:
- Climate Change: includes rising ocean temperatures, rising sea levels, coral bleaching, extreme weather events (including increased frequency of intense rainfall and severe cyclones) and ocean acidification. Sea temperature controls the rate of reef growth, dissolved oxygen levels and distribution & diversity of marine life. Increased temperatures also cause coral bleaching. Rising CO2 levels increase the amount of CO2 absorbed by the sea, which is then converted to carbonic acid and causes acidification. This also leads to reduced quantity of calcium carbonate for shell formation.
- Declining water quality (from over-land runoff): from inland rivers (esp. during flooding), chemical runoff from farming, mining, etc.
- Coastal Development: mainly the urban centers and their associated activities are putting reefs at a risk.
- Illegal Fishing: overfishing of natural predators and associated pollution from boats
- Marine Debris
- Starfish outbreak: increased agricultural runoff and overfishing of its natural predator cause outbreak of Crown of Thorns starfishes who predate on coral reef.
It is estimated that the reef's ability to recover may be on decline as a result of combination of these factors.