I was curious, and found this: https://en.wikipedia.org/wiki/Crown-of-thorns_starfish#Ecolo...

They are 25-30 cm starfish with up to 21 arms, and they damage the reefs. It does say that "warmer sea temperatures enhance larvae development", with this reference: http://www.nature.com/articles/srep08402

This was interesting too:

"An autonomous starfish-killing robot called COTSBot has been developed and as of September 2015 was close to being ready for trials on the Great Barrier Reef.[84] The COTSbot, which has a neural net-aided vision system, is designed to seek out crown-of-thorns starfish and give them a lethal injection of bile salts."

More on dredging: https://fightforthereef.org.au/risks/dredging/

Also an issue in Florida: http://voices.nationalgeographic.com/2016/06/17/from-miami-t...

"Florida is home to the U.S.’s only living barrier reef and world’s third-largest coral reef system"

I'm not sure about that. CoT has been a problem for a long time. Silt is a problem close to shore, but the extent of bleaching in recent years is unprecedented in terms of sheer area of decimation: http://www.abc.net.au/news/2016-11-29/reef-great-barrier-ree...

Fertilizer run off from agriculture (mainly sugar cane farming) is also a huge problem [1]. Not sure if they're actually getting any better with this or not...

[1] https://www.qld.gov.au/environment/agriculture/sustainable-f...