Coral reefs are fragile ecosystems, and even a slight change in their marine habitat could have a drastic impact on corals, as well as other marine species. One of the biggest threats to reefs is climate change. As global warming occurs around the world, ocean waters will also begin to warm, known as ocean warming. Even a 2 degree Celsius change in the water can have a significant impact on corals. Indeed, the corals can sense this slight change and will start to feel stressed, and their first natural reaction is to expel their symbiotic zooxanthellae since this algae is not one of them. At this point, the corals are now hopeless without their symbiotic partner and will not be able to survive without oxygen and food. The corals, now starving, will turn ghostly white and perish. Since humans need healthy coral reefs to be able to fish, it makes sense that they would want to protect the reefs. But on the contrary, overfishing and destructive fishing have become another threat to the marine ecosystem. Not only do corals protect fish, but fish also protect reefs by keeping them clean and providing them with nutrients and food to thrive. If there weren't enough fish in the reefs, the corals wouldn't be able to survive. Destructive fishing also causes enormous damage to reefs because on some reefs people have large nets to catch fish. This technique is not only useless, but also harmful because the nets only catch on the corals, breaking them and the fish. . Some fishermen pour a chemical into the water to stun the fish so they can catch them, but the chemical is very harmful to the corals and will eventually kill them. Natural disasters only happen once in a while, and so... middle of paper...... conditions eventually led to the bleaching of a huge amount of corals, and caused a total of 70 to 80% of all shallow water corals die. However, weather isn't the only threat nature poses to coral reefs. Invasive species and coral predators also pose threats to corals. The crown-of-thorns starfish (Acanthaster planci) is one of the predators of corals. They slowly crawl over the corals and literally “eat their life” by consuming all the living tissue of the corals, then move on to the next coral. Other predators of corals include fish, barnacles, marine worms, snails and crabs. In 1978, a massive number of crown-of-thorns starfish invaded the reefs of Fagatele Bay National Marine Sanctuary in American Samoa. This was an extreme case of predation which had devastating results as 90% of all corals in the sanctuary were destroyed..