Leafy Sea Dragon circa 2003, over a decade ago.
I made this image at Birch 13 years ago. Back then flash was allowed on these Leafy Sea Dragons, but no longer. Lucky they allowed flash because the camera I was using did not make an acceptable image over ISO 200. Flash allows one to shoot in Manual Exposure Mode where one can experiment and get a decent ISO, aperture, and shutter speed with practice.
Without flash, one is at the mercy of often lacking ambient light, a fast lens like F 2.8 or faster, and a camera that has relatively grain reduced ISO at high numbers, such as ISO 5000.