Underwater photo/video gear

I've been diving for a while, I've done diving with camera gear before, but never done it professionally. I am however very good at it.

Two things:
1) I am going to school for Marine Biology, and I will be required do scuba dive and take photos/videos for research purposes.
2) Before this diving research term (begins Summer- 2017), I will be working at a dive center where I was trained as a photographer/videograp​her for their guests & customers. (Above & below water)

I only own a Sony RX100. Sold my DSLR and all my gear.
Its not a bad camera, and using it for photos above water would be suitable.
But Im not sure about underwater. Would it be okay?

OR...

I was thinking about the Sony a7SII for the underwater photo/video (especially for my research purposes.)
Would be great for the video work, but iffy on the photo abilities.

Thought?

RX100 was once regarded as the best underwater DC ever made. You can buy inexpensive housing from Meikon