When diving around piers/docks at night, you need to be really careful while diving - they move pretty fast. I got nailed by one of the black ones a year ago - he crawled under me while I was taking a picture of a critter on a pier leg. I had checked beneath me when I set up - it was clear, after the picture, I lowered down to turn around and swim clear and took a hit right in the thigh (went right through a 3 mil wetsuit) - it hurts
, and took a couple weeks for all the little pieces to work out.