Elysia bangtawaensis or mangrove-leaf sea slug is our local species although is is found from the Queensland border to Thailand and even India. The species was only named in 1998 after a Thai village that resisted clearing of mangroves for aquaculture. It was then discovered at Coolangatta by another consultant during impact assessment for a road project. Soon after I found some at Half Moon Bay, near Smithfield, Cairns - I was the second person to find the species here and reported the find to the sea slug forum. In the photo below there is a Telescopium snail for scale. Elysia are about 4 cm long.
This time, I found the mangrove sea slugs in a Ceriops forest. Ceriops or yellow spurred mangrove inhabits the dry intertidal areas near salt pans and is not the place one would expect to find sea slugs. Ceriops forests are rather unexpected places for most Australians.
Elysia were in very shallow pools on the floor of the forest. Not every part of the forest had Elysia, they are fairly scarce and I had not seen any for years. I am not sure if they are always present or if they come and go. I am sure that they can be very hard to find. They do not seem to chase sun spots which I would have expected them to do if they were solar powered.