Dolphin encounters are typically fast paced with lots of swimming. Individuals in a pod will pass very close to you, but at high speeds so you don't have time to experiment much with light and settings.
Close Focus Wide Angle is one of the "oldest tricks in the book" for many professional photographers, and has graced many magazine covers.
The perspective in an image shot with your dome port half submerged provides a sense of scale that is unique. Also called over-unders, many photographers consider these the most difficult category of wide angle images to capture.
These settings will get you started in dark environments when only a small amount of ambient light is shining in.
For use in a wide variety of salt water environments including the Caribbean, Red Sea, Australasia and South Pacific when you have at least partial sun up to about 30m (100 ft).