- Look for spawn. Nudibranchs all lay slightly different shaped egg masses; these are usually white, but may be pink, yellow or orange. They are usually conspicuous and are laid in prominent places. Search nearby for the animal, which may be beneath a rock or at the base of the hydroids or bryozoans on which the eggs are laid. Try collecting clumps of hydroids with eggs on and leaving these for a few hours in trays of seawater, when the animals will probably crawl out or float upside down on the water surface.
- Look under rocks and at night. Some Aeolids and many Dorids are nocturnal, especially in the tropics. They may be easier to find at night, when they come out to lay eggs, or may be found in the daytime by turning over loose rocks, broken corals, etc. Take care to turn any rocks back after searching under them.
- Know the likely food of your animals. Sponge feeders will usually stay on their food and move about very little, except to lay eggs. Sponges are commoner in deeper water, in caves, under overhangs and under rocks, in places more or less out of the light. Bryozoan feeders are somewhat more active, but are again usually on or amongst their food. Hydroid feeders are quite active, and are usually found amongst their food or crawling nearby. Soft coral and coral feeders are often well camouflaged and may eat their way into the food, or live near the bases of large colonies. Some nudibranchs feed on burrowing anemones or sea pens and may burrow in gravel, sand or mud.
The Conchological Society of the British Isles operates a recording scheme for Marine Molluscs and is keen to receive records of nudibranchs, which are usually under-recorded, from anywhere around the British Isles coastline. An Atlas of British Marine Mollusca has been published and updates are produced at intervals.