The Great Barrier Reef must contend with ocean warming, acidification and extreme weather to stay alive amid record heat waves. A third of the natural World Heritage sites are currently being threatened by climate change, the IUCN reported. The Great Barrier Reef has endured three mass ... geology, ecological processes, and species and habitats. While both humans and natural life are having a negative impact on the reefs prosperity, the reef is so diverse that until now, it has been able to overcome a lot of these destructive forces. Climate change poses the greatest threat to the world’s natural heritage, with the Great Barrier Reef now in a “critical” situation, a report has warned. In addition to the Great Barrier Reef, the islands and protected areas of Mexico’s Gulf of California have also entered the critical category, the report found. The reef is the world’s most extensive stretch of coral reef with over 1,500 species of fish and about 400 types of coral. In addition to the Great Barrier Reef, the islands and protected areas of Mexico's Gulf of California have also entered the critical category, the report found. The reef, the most extensive in the world, houses more than 1,500 species of fish. Previously, invasive species were listed as the top threat. In one year, two crews working full … ... along with Ningaloo and Shark Bay, also face threats of invasive species… The Great Barrier Reef is the largest expanse of coral reef on the entire planet. The Great Barrier Reef's 600 or so species of echinoderms—the order that includes starfish, sea stars, and sea cucumbers—are mostly good citizens, constituting an essential link in the food chain and helping maintain the reef's overall ecology. Harmful invasive species could be introduced into the Great Barrier Reef ecosystem due to a rise in shipping activity to service Queensland's mining boom, a Federal Government adviser has warned. Crown-of-Thorns Starfish – This particular species of starfish is an invasive species in the Great Barrier Reef and can cause a lot of damage because it feasts on coral polyps. After climate change, the next two significant threats to these natural sites are invasive alien species and tourism impacts. After the climate emergency, the next two largest threats to heritage sites are invasive alien species and tourism impacts. For example, in 2015 the Great Barrier Reef was home to anywhere between 4 and 12 million crown-of-thorns starfish.