I came across a pair of pelagic nudibranchs mating during a blackwater scuba dive, while drifting in the ocean in the darkness of night, over 700 feet of water, in the Gulfstream off the east coast of south Florida. During such a dive, one can witness the largest migration on planet Earth that occurs every night, with creatures living hundreds of feet below the ocean surface swim toward the shallow depths, larval stages of marine creatures spending their early life, permanent residents (pelagic animals) as well as deep water animals that migrate vertically at night to feed. I approached slowly, so as not to disturb them, and was able to capture a few images of this fascinating and rarely seen underwater animal behavior.