Really nice, Jo, especially the 2nd part. Some great shots there. The morays mating, the lionfish close-ups, the morays behind the lionfish, and the lovely final shots of that colorful reef. And that sea grass dive looks great! I didn't know the Red Sea was that interesting! Makes me want to go.
Agree with Drew about the topside shots. If you don't have a tripod with you then lean/brace the camera solidly on something and keep it to static shots and perhaps the odd whip pan, which you can just about get away with handheld. It took me a long time to really grasp that but it really makes a difference between a pro and amateur impression. Better still, unless you have some particular need to promote the hotel, cut down on the opening topside shots and get underwater a.s.a.p. to hold your audience.
Also in some places I would say you have too many similar shots of the same thing, such as the longnosed pipefish in the seagrass. If the shots are so similar in angle and magnification it makes them difficult to edit smoothly together, and they don't really add much, so maybe include fewer of them and let them run a little longer. Ideally you want a significant change in angle (>30 degrees) or magnification between consecutive shots of the same subject. Then they should fit nicely together with a straight cut. You have quite a lot of short dissolves that I thought were unnecessary. If a shot looks like it could more or less be a realtime continuation of the previous shot (e.g. the series of shots of the emperor shrimp on sea cucumber starting at 1:05) then just straight cut it. Save the dissolves to signify a lengthy gap in time or if you really need them to smooth out 2 similar shots that would otherwise jar with a straight cut. You'll hardly ever see dissolves on big u/w productions. I may have said this before, so apologies if I'm repeating myself.
One other thing is that the voiceover is great but is slightly tinny and deserves a better mic/sound card. Um... I may have said that last time too 