WINNER, Animal Behaviour
I found these beautiful floating pelagic nudibranchs in a low tide rockpool early one morning, along with hundreds more. They had been washed there overnight during onshore winds and these two looked like they were squaring up for a fight!
Port Kembla, New South Wales
Nikon D810, Nikkor 105mm f/2.8 micro, 1/320, f/32, ISO 64, 1 x Inon Z220 strobe, full power and fibre optic snoot, Aquatica Digital AD810 with low-profile macro lens port