As to barracudas, if you're not wearing anything anything shiny and don't panic, they will leave you alone. At least the ones I've been around have left me alone. No trouble from the sharks, turtles, lobsters, lion fish, and other "dangerous" sea creatures I've been around.
But, I did have a pesky icthus obnoxiata, aka shark wah-nah-bee, give me a rough 15 minutes. He, all nasty creatures are "he", kept circling, and circling, looking for an opportunity to attach himself to my poor, tiny body. I whipped out my dive knife and kept jabbing at him. A time or two I grabbed him around the caudal pedestal and attempted to sling him away. Do you have any idea how hard it is to sling a fish underwater? My dive buddy was worthless. He was having a little trouble himself because he was laughing so hard. Choked on the air in his regulator he did. Served him right if he had drowned. Anyway, after a tense hand-to-fin combat, the icthus obnoxiata took himself off and looked for whale shark or some other creature to attach to.
That is the worst trouble I've had in the deep blue. I usually swim off the northern coast of New Guinea, Pantain Harlin, outside of Depapre.
I was on the Great Barrier reef on some tour boat. They even gave us scuba diving lessons.
“Okay - this is the breathing thingy. The breathing thingy goes in your mouth. Don’t breath through your nose! Breath through your mouth. Have fun!”
Stupid I suppose - but it was pretty cool. Even saw a big shark and tried to swim towards it (!?) and saw one of those huge GIANT clams like in the Popeye cartoons. Of course you could see forever and no crawl spaces to get through.
Snorkeling on the shallow reefs was prettier though - about the only thing I’ve ever done that I was really in awe of.
Most of the time I’m like “Huh - the Grand Canyon has a lot more color in the photographs.”