I have dived with cow sharks, gully sharks, reef sharks, ragged-tooth sharks, moray eels, rays of various types and sizes, seals, gigantic and very, VERY aggressive red Roman, potato bass and southern right whales. 95% of my diving has been in the Great White infested waters of False Bay and Hout Bay off Cape Point and a friend of mine, Dean, came within spitting distance of a Great White. All of the species that I mentioned are either dangerous predators, known to be aggressive, look scary and dangerous but aren't, are big enough to unintentionally hurt a diver or are prey species likely to attract predators. For my very first non-cert dive I dived about 50 metres away from a big Cape Fur Seal colony. Dean dived with a Great White in the area of his final OW cert dive and found out later that they had been hunting earlier that day with wounded seals in the water.
You want to know the most scared I have ever been in the water? Well, most scared due to an animal. It was a dive with a reef shark about half a metre long. That little bugger scared me SILLY and the only reason it was so aggressive was because Dean and I had a bunch of inexperienced newbies doing their night dive for AOW that were scaring it SILLY. They were unintentionally herding it and preventing it from going where it wanted to go so it did what most predators do when threatened and acted aggressively. I have similarly been scared by Red Roman guarding their territory. That is right, I've been more scared by fish no larger than my fins than by sharks bigger than I am!
My point? Getting attacked by a sea creature unprovoked is virtually unheard of. Granted, my experiences are only anecdotal, comprise a tiny portion of all of the data points available and this board is littered with men and women whose experience dwarfs my own, but if you do your research you will struggle to find any reports at all that were not instigated by human behaviour. This thread is littered with statistics and relative levels of danger but my favourite, because it is so evocative and downright silly, is that more people are killed
falling off chairs than by sharks each year. You want to stand up for the rest of your life?
On the other hand, even the smallest sea creatures can turn into a 'Finning Ball O' Death' when cornered, provoked, teased or irritated.
Edit: there have been a handful of people attacked by Great Whites in False Bay over the last decade or so that I have been diving. One of the attacks was even [erroneously] reported as an attack on a diver. Needless to say that these attacks have garnered a lot of media attention and probably even more attention from the diving community. Every single one of those attacks was either on a swimmer, surfer/body-boarder or spear fisherman. NONE that I have been made aware of have been on divers.