Chris & Monique Fallows / Cape fur seal (Arctocephalus pussilus) portrait, at water surface, Seal Island, False Bay, Cape Town, South Africa.

Juergen Freund / Halligan Bay, where land meets water of the salt field and thousands of dead bugs, fish, rodents and birds are washed ashore. Lake Eyre, South Australia

Alex Mustard / Indo-Pacific sergeants (Abudefduf vaigiensis) swimming in mix of salt and freshwater, which is creating a haze in the water. Tulamben, Bali, Indonesia. Java Sea.

Alex Mustard / Nudibranch (Flabellina lineata), taken in the field in Gulen, Norway. North East Atlantic Ocean.

Alex Mustard / Nudibranch (Flabellina lineata) photographed in the field aquarium, Gulen, Norway. North East Atlantic Ocean.

Alex Mustard / A nudibranch (Polycera quadrilineata) photographed in the field aquarium, Gulen, Norway. North East Atlantic.

Alex Mustard / A nudibranch (Onchidoris muricata) photographed in the field aquarium, Gulen, Norway. North East Atlantic.

Alex Mustard / A nudibranch (Cuthona viridis) photographed in the field aquarium, Gulen, Norway. North East Atlantic.

Alex Mustard / A nudibranch (Cuthona viridis: Trinchesia viridis) photographed in the field aquarium, Gulen, Norway. North East Atlantic.

Alex Mustard / Light and dark colour morphs of (Acanthodoris pilosa) nudibranch. Photographed in the field aquarium, on location in Gulen, Norway. North East Atlantic Ocean. Digital composite.

Alex Mustard / Nudibranch (Limacia clavigera), taken in the field aquarium, Gulen, Norway. North East Atlantic Ocean.

Alex Mustard / A nudibranch (Eubranchus pallidus) taken in the field aquarium, , Gulen, Norway. North East Atlantic.