To be fair, some of the sounds recorded are real. I can always hear the chromis and clown fish grunting (if that's the word). They make a distinctive sound and it's clearly audible in the water. Parrotfish crunching the corals and even big shoals of gape mouth mackerel make a clacking noise as they swim through the water.
I am privilidged to say that I have personally seen turtles fighting over a cleaning station and an octopus and grouper co-operatively hunting with my own eyes. Diving and experiencing the underwater world is a great privilidge that we all share and we sometimes forget that for millions/billions of people this is something that they will never see.
The Coral reef episode is not likely to be ground breaking for those of us who have been there and seen those things with our own eyes. But for others it was a wonderful, colourful hour of entertainment.