Do they prefer the food of their infancy because it tastes better, is more nutrient-rich, or is easier to eat?  Maybe they are just nostalgic for the food they ate when they were young.

Two-month-old Elysia clarki having an early morning crawl among the turtle grass and manatee grass in Box of Slugs 2. 9/29/18

A few of the youngsters from the most recent brood have moved in with their mom in the tank at home.  They were weaned from Bryopsis plumosa to B. pennata once they were a few weeks old, and have been growing steadily.

For a few reasons, not all logically sound, I had assumed B. plumosa would be harder to culture.  If an aquarist has a problem with Bryopsis, it is invariably B. pennata.  Combined with the fact that B. plumosa is crucial for hatchling survival, and that I had to travel all the way to Tampa to get it, I figured I would have trouble keeping it going.  As a consequence, I always shift young Elysia to B. pennata when they were ready to eat it.

Despite my preconceptions, B. plumosa is thriving at this point.

Bryopsis plumosa culture tank (surface is 10″ by 20″), stuffed to the top with algae. 9/14/18.

To the uninitiated, the B. plumosa tank would look like a mat of unruly glop. To an aficionado such as myself, it looks like an actively growing, unruly mat of precious food for hatchling Elysia.  It is a “half-ten” aquarium: a ten-gallon tank, but only half the height (OK, so it is really only a 5-gallon tank), which provides a lot of surface but only a few inches of depth.  The growth form is very different from B. pennata, which tends to be long and feathery.  B. plumosa grows more like clumps of moss.  I am concerned about the tank being taken over by B. pennata invading from elsewhere in the system, but so far so good on that front.

At the moment, the growing conditions are:

• Nutrient dosing at about 150:30:1 Carbon:Nitrogen:Phosphorus, plus Guillard’s F/2 at 2 ml/day (note this is the whole system, not just this tank).
• Circulation using a powerhead and rotating output (see Slug Safe Circulation).  Trust me, it is in there somewhere.
• Lighting by an Evergrow S2 hydroponics light, about 6″ from surface.

To get to the point of this post, I had enough B. plumosa to throw some to the adults.

Elysia clarki eating Bryopsis plumosa in Box of Slugs 2. 9/26/18.

Unsurprisingly, the slugs ate it.  I did not expect, however, that the largest female would rarely leave the clump of algae until it was completely consumed.  She very much preferred the plumosa. I brought another clump home, and she is still sitting on it, along with one of her kids.  The tank is full of B. pennata, at all levels, but the slugs stick right to the single clump of B. plumosa on the surface.  It may be my imagination, but the big one seems larger and more colorful after a few weeks of eating B. plumosa.

Box of Slugs 2, with plenty of Bryopsis pennata among the turtle grass. 9/26/18

So, anecdotally, even grown up slugs prefer B. plumosa.  Another thing to put on the list of things to test more rigorously.  For now, one can speculate about why they seem to prefer it, and what cues (smell? texture?) draw the slugs to the algae.

Fat Babies Have No Pride

In the meantime, another brood has hatched and has started to grow.  I am not sure why (I am not in any way a musical person), but when a new brood starts to eat, Lyle Lovett’s “Fat Babies” runs through my mind almost continuously.  I have no idea whether the song has a subtle, subversive message (if so, I apologize for any offense), or whether it is simply about chubby infants not being proud.

Juvenile slug crawling among B. plumosa, with diverticula full of chloroplasts. 9/28/18

They are feeding and growing, and it looks like we’ll have several dozen ready for activities in the spring.

That’s OK.  Who needs pride?