Coral reefs are the one of earths most complex ecosystems, containing over 800 species of corals and one million animal and plant species. Here we see a shallow coral reef that contains Mountain coral (Porites lutea), suffering from bleaching. Coral bleaching occurs when corals are distressed and dying due to the ocean temperature rising. This stress causes them to expel endosymbiotic algae leaving only the dead skeleton. Footage obtained whilst scuba diving at Phi Phi islands, Krabi province, Thailand.