As reported by the American Atmospheric Administration NOAA, currently a global coral bleaching takes place in the world's oceans. High water temperatures are attacking the reefs, which makes them lose their color and, ultimately leads to a huge die off of the corals over time. It is the third global coral bleaching on record.
The problem is that corals need algae to survive. The algae make food by photosynthesis and pass some of this food on to the corals. They also help the corals to make their limestone skeletons. In return, corals provide a safe place to live and a supply of nutrients in their waste products. Since algae provide energy through photosynthesis, they also give the corals their color. However, if the sea water gets too warm, the algae increasingly produces toxins. In order to protect itself, the coral repel the algae and thus lose not only their color but also their main source of food. After only a slight bleach the cnidarians have the strength to recover but if the algae stays for longer than approximately two months, the corals die off.
A dying of animals in masse form, could lead to collapses of whole reefs which means that an extremely important line of defense, which protects the coast of any storms, is in danger. In addition, the dying of corals also shrinks the habitat of many fish.