Although they will eat a number of algal species, Elysia clarki strongly prefer Bryopsis, which is a feathery filamentous alga considered by most aquarists  to be a pestilent nuisance.  For the past year, I have been benefiting from the struggles of a local reefkeeper who has had a plague of the stuff in his 500 gallon system.  Alas, through rigorous reduction of phosphate levels, his battle  with Bryopsis seems to be coming to an end.

That sent me into a panic.  Well, more like mild anxiety.  Even though it has been possible to maintain my own stock of Bryopsis, it had started to run low.  Hard to believe, but I am having trouble growing enough of a nuisance alga.   In my defense, it is a bit of a trick to grow one form of plague without another taking over.  I was starting to be concerned that the slugs would not be ready to lay eggs if they ran out of their favorite food and had to make do with other algae.

Fortunately (for me), another WAMAS member is in the midst of a battle with Bryopsis.  It required a trip to Virginia, but I returned with a bucket full of soft, feathery algae.  It seems finer than the variety I was getting from the previous source.

Nonetheless,  the slugs are lapping the stuff up.   Despite their reputation for slow movement, slugs are pretty good at moving around when they have appropriate motivation.

Elysia clarki on new batch of Bryopsis, 9/3/15

The adult above dug right in.  As did the juvenile, below.  Up to her rhinophores in Bryopsis.

Young E. clarki feeding on new Bryopsis, 9/3/15

Below is a shot of her cruising around, before having found the food pile.

Young E. clarki, exploring. 9/3/15

Now that they have been fattening up on algae, they have taken on a much deeper green color.  Will have to post some before and after photos next.