According to a recent article in The Guardian (June 7, 2016), what appears to be the longest and probably worst global coral bleaching event in history is accompanied by the smell of death:

“I can’t even tell you how bad I smelt after the dive – the smell of millions of rotting animals.”

said Richard Vevers, CEO of the Ocean Agency non-profit, which is documenting the coral bleaching event in the Great Barrier Reef.

See the original article here: http://www.theguardian.com/environment/2016/jun/07/the-great-barrier-reef-a-catastrophe-laid-bare