Underwater Light Reflector?

I'm new to photographing underwater. When I take portraits above water I like to use a reflector to bring in some extra light to my subject without using a flash. Does anybody use something like that underwater? Is it even effective?

Thanks.

I don't know about without a flash, there's very little light underwater to make much use of. However if you are using a strobe, it is possible to mount blank white slates in positions that other strobes may be found in - these reflect the light from the main strobe. However as the light from the strobe has to travel from the strobe to the subject, back to the slate, to the subject and to the lens of the camera, a fair bit of light is lost, however in very clear water can work alright.

Another option would be to use a torch to reflect light off slates/mirrors onto the subject, as this would create a more subtle light. However again only works well in clearer waters.