man: the crown of thorn is very poisonous. 1997, bali barat lose nearly 50% of coral life. and we make, like, big expedition to remove them away from coral. alling: nono is known as one of the greatest naturalists in the northwest bali region. he's trained as a lawyer, but his life's work, his care, is for the environment. suparno: and we kill more than 700,000s of crown of thorns. dustan: i went to bali in 2011 and was awestruck by the reefs i saw. this is in the very base of the coral triangle. it's sort of the mother, if you will, of coral-reef biodiversity and of all marine biodiversity. and i've been going there annually since. and what this video depicts are the changes we saw before and after a very severe heating episode, caused in part by el nino and global warming. this is the story of what happened to the reef in one year. so this is a healthy coral. we call it the monument coral. we have a temperature probe underneath that records the temperature of the sea water every 30 minutes. so we have very good temperature records from this part of the ocean. so this coral