Atolls as in the type of island
Have there been any cases? Fish are easy birds catches fish flys away fish falls out in the water, what about bigger creatures? What is the biggest sea animal that has got stuck an in Atoll?
Oceans levels change so slowly that I can’t see any just getting stuck there in a small space as the land surrounds them a half in a year.
No, atolls are islands. Man eater sharks hardly ever come onto dry land.
I suspect that you mean to ask whether they ever come into lagoons. And the answer to that is that they sure do. The height of a coral atoll is largely dictated by the height of the lowest tide of the year. Few corals can stand being dessicated for more than a few minutes, so the reef only grows below the low tide mark. The atoll can become higher in places due to sand buildup, but it must remain lower than low tide at one point at least, otherwise the lagoon silts up and ceases to exist.
And of course because the atoll at some point is only at low tide level, sharkscan and do swim in during high tide, when the water may be several metres above the reef.
Ocean levels change rapidly, twice a day, every day.
Also, very few lagoons have a completely unbroken reef. Most have deeper channels through which sharks, ships and pirates can enter.
IOW, “none atoll.”
I would normally stand for such a pun, but in this instance islet you off.
Sneaky, napster downloading MP3 parasites. Even when I thought it was the sharks I knew it was the pirates 
Ha! No lie, dude, it was like years before I had one.