Studies show that most of the excess dissolved inorganic nitrogen and phosphorus comes from fertiliser use on land. Excess nutrients can also increase coral bleaching susceptibility and coral disease. Impacts can include increased coral-eating crown-of-thorns starfish outbreaks, increased macroalgae abundance and algal blooms which can take over and reduce coral diversity, and reduced light available for corals and seagrasses. However, if excessive amounts of nutrients, notably nitrogen and phosphorus, are brought in through land run-off, this can upset the natural balance of the Reef systems. They are the natural chemical elements and compounds that plants and animals need to grow. Nutrients as they occur naturally in Reef ecosystems are vital. Poor water quality, including nutrients, sediments and pesticides flowing from the land to the Great Barrier Reef from activities like agriculture, is a major threat. The higher the levels of atmospheric CO 2, the greater the impact on water quality.
![the barrier the barrier](https://4.bp.blogspot.com/-QSdB0s0evy4/WzaeLY2nlmI/AAAAAAAADxs/MO0k4TXjs0wDjT3T64W41mMdnVlpFnFBACLcBGAs/s1600/Thames%2BFlood%2BBarrier.jpg)
Linked with climate change is ocean ‘acidification’, which is caused by the oceans absorbing about a quarter of all carbon dioxide (CO 2) released into the atmosphere. Climate change is predicted to increase the intensity of extreme weather events such as cyclones and floods. Scientists know that sea surface temperatures of the Great Barrier Reef have increased by 0.8☌ (on average) since the late 19 th century and will continue to rise. If these events are severe and frequent enough to hinder recovery, coral can die.
![the barrier the barrier](http://nbcfellowship.org/wp-content/uploads/2018/06/breaking-through-the-barriers-2-1280x720.jpg)
Increasing water temperature is one of the main causes of coral bleaching, which is becoming more common. The most dramatic impact of climate change is on coral and other species. The cumulative impact of climate change, land run-off and other threats is testing the ability of the Reef to recover from major disturbances. The biggest threats to the Great Barrier ReefĬlimate change is the single biggest threat to the Great Barrier Reef, as it is to many ecosystems around the world.