StiX floats are the easiest way to lighten up a heavy DSLR system underwater. Made by 4th Generation Systems, they are easy to put on and can be cut away as necessary.
Ring lights have long been a popular way for macro photographers to get bright, even light directly onto small subjects.
Due to the magnification involved, macro photos can consume a lot of light. Underwater photographers have long struggled to get their camera housings with two strobes into tight spaces, or get the lights positioned close enough to the front of the lens without creating lens flare or shadows from the port.