At least a little.

As often happens, I kept too many babies from a recent brood, and they rapidly consumed the large growth of Bryopsis in their tank., Algae production was a little slow in the system, so I chose to reduce their ration.  I did not exactly starve them, but there was not always Bryopsis in the tank.  There was , however, quite a bit of the pest algae Valonia,  known as “bubble algae,” because it grows as clusters of large unicellular vesicles.  Although I periodically have tried to remove it, it was thriving in the tank with the young slugs.

Elysia clarki, about 3 cm long, with empty Valonia bubbles. A large, empty bubble can be seen by the slug’s tail. 2/26/19

The slugs appeared to be feeding on the algae, and some of the bubbles, which are normally intense green, became clear.  Although it would require DNA sequence analysis of the slugs’ kleptoplasts to be certain, the circumstantial evidence indicates that they are sucking sap from the algae.  It makes sense, because Valonia bubbles are large single cells, which would allow a slug to have a big meal with just one puncture.

A recent paper by Mike Middlebrooks and collaborators (Biol. Bull 236:88, 2019) demonstrates that Elysia crispata (with which E. clarki is most probably synonymous) eats a wide variety of algae in the wild.  In the aquarium, it looks like we can add one more species.

The good news is that the slugs seem to be wiling to make use of Valonia when necessary.  Unfortunately for anyone with an outbreak, the slugs consume them so slowly that there is little chance they would eradicate an infestation.  

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?

In only a few weeks, the first batch has gone from barely visible (see the previous post) to nearly adult.

A week ago, it was time to move the four survivors into tanks with the grownups.  They had been weaned from Bryopsis plumosa to B. pennata, and were big enough to avoid being eaten by most of the worms and amphipods that inhabit the boxes of slugs.  As far as I can tell, they all survived once their rhinophores and parapodia were fully developed, so they are sturdy little gals.

This is the best photo I could get last week of a youngster exploring her new world in the home tank.  I found her egg mass on 12/30/17, moved her to the USG system, grew her up, and now she’s home!  She’s a little over 1 cm, I would guess, and mom (dad?) towers over her.  Elysia look about the same whether they are happy, sad, scared, excited, angry, or bored, so I am not sure if the parent slug looks proud.

Baby Elysia clarki, below mom’s head, in Box of Slugs 2.0. 2/18/18.

After only a week of stuffing herself full of Bryopsis, she has nearly doubled in size.  Still dwarfed by mom, but on her way to adulthood.

Young Elysia clarki, with her mother. Box of Slugs 2.0, 2/25/18.

As the older of her parents becomes paler and slowly slides into senescence, it will soon be time for the little ones to take over as matriarchs.  We’ll see how long it takes before they produce their first eggs.

After passing the first hurdle, getting them to eat, everything should be easy, right?  Well, there are plenty of things that can go wrong.  Predators can sneak in with the food algae (you don’t have to be too big to eat a lot of hatchling slugs), and pathogens can decimate a whole brood.  Nonetheless, a few of the first batch have grown, sprouted rhinophores, extended parapodia, and look like teeny Elysia!

Miniature E. clarki, about 10 days after first meal. 2/5/18

They are currently living in a modified specimen container (like they use to catch fish at the pet store).  I drilled a few big holes in it, and covered them with fine nylon mesh to keep the babies in.  They get a constant, slow flow of UV-sterilized artificial seawater, and have a variety of algae to choose from.  They still seem to prefer Bryopsis plumosa for the moment, although they may be sneaking tastes of B. pennata.

Teeny E. clarki at about two weeks after first meal. 2/8/18.

It has been hard to get a proper measurement at this point, but they are about 2 mm long, are somewhat visible to the naked eye, and can be easily observed with a simple magnifying glass.  The photos above were shot with the macro setting of a digital point-and-shoot camera, so they are rapidly leaving the microscopic world!

Fingers crossed that they continue to grow.