Things have been going quite well in the in-line refugium known as Box of Slugs 2.0.  Although it might not be considered a plus in most aquaria, algae have been very successful in the new tank.  A less sophisticated aquarist might dare to call the tank an eyesore, yet the slugs could not be happier.  Here are a few of the youngsters grazing on what I think is Derbesia.

Trio of Youngsters, Box of Slugs 2.0

Indeed, it has been a great time for the little guys, and they have been growing like the little slug-weed chimeras that they are.  Many have gone beyond the twiggy little worm stage to looking and behaving like proper small slugs.

At this size, I am still unsure that they are all E. clarki.  The one below is most likely E. tuca almost looks like E. chlorotica, or maybe E. subornata, and does not have much in the way of parapodia.

tuca chlorotica not clarki?

The small slugs below look more convincingly like the adults in the tank.  Rolled rhinophores, parapodia starting to ruffle, chloroplasts throughout the body, including the foot, all point to the little guys being the common lettuce slug of the Keys.

Young E. papillosa clarki, 2/8/15

Baby slug exploring

Will they get spots and ruffles like the purported parents?  Time will tell. [note added later: these are not young E. clarki, as a few of the edits above indicate]

Adult E. clarki 2/5/15

They still have a long way to go to get to full size, as can be seen in this photo of the adult from the photo above grazing on Bryopsis while a youngster wanders about.

Growing baby and parent 2/13/15

One of the more interesting developments is the appearance of very small, dense egg masses in Box of Slugs 2.  At first, I attributed them to the small herd of E. crispata that arrived a few weeks ago, since I have no idea of the size or appearance of their egg masses.  I need to start putting a ruler or something in the photo for scale, but this clutch is about the size of the first coil of the a standard E. Clarki mass from Box of Slugs 1 (shown here, for example), and the little embryos are packed much more tightly.

Egg Mass 2/13/15

As mentioned above, I thought these were eggs from crispata, but was thrown for a bit of a loop when I saw one of the youngsters curved around the mass as if laying them.  Can they really be mature enough to lay eggs?  I collected the mass below, and am documenting the embryos’ development.  They are definitely fertile, as indicated by the classic circling movements inside their eggs, and maybe this time I can get a brood to mature in a controlled environment and find out which species they turn into.  Stay tuned.

Life cycle of Elysia clarki in the Box of Slugs

The slug colony, a.k.a. Box of Slugs, has been doing pretty well overall.  The slugs have been eating, growing, mating, and laying eggs.  The eggs have been hatching, and the veligers have settled as baby slugs.  Of the many broods that have been deposited over the past few months, I have collected and hatched about a dozen, so producing juvenile slugs has become routine.

What has been puzzling and frustrating is that the baby slugs are not maturing beyond the first few days.  They crawl happily among the macroalgae in the little dishes, but never seem to take in chloroplasts or develop parapodia or rhinophores.  I have offered them both Bryopsis and Derbesia, two algal species that are supposedly their favorite first foods, and they appear to be attempting to eat, but the little guys never turn green.

A few observations may or may not be relevant.  First, dumping too much Bryopsis into one of their dishes appears to cause immediate and permanent cessation of activity.  The simplest interpretation is that, even though Elysia species have been reported to take advantage of the defensive compounds produced by their food plants, too much is simply too much.  Also, even though I dip the algae in distilled water for 30-60 seconds before adding it to the cultures, the occasional amphipod, copepod or nasty looking worm sneaks in and may cause a ruckus.

In the end, there are hypotheses to be tested.  In order of decreasing likelihood:

1.  I am using the wrong food plants.  Even though I am feeding species of Bryopsis and Derbesia, the algae were collected from aquaria, so their origin is unknown.  I know that the parents love the species of Bryopsis that I am providing, but it may be more difficult for the juveniles to feed on.

2.  Temperature.  I am currently not controlling their temperature.  They hatch on a bookshelf at about 23 degrees C, and then their dishes are moved to the top of the Box of Slugs to provide light when the algae are added.  The temperature is probably a bit higher under the LEDs, but I have not measured it.

3.  Light.  They go from low to relatively high illumination when food plants are added.  Maybe they don’t like the light.  The little slugs move around happily enough, but who knows.

4.  Chemistry.  Aside from keeping salinity at 1.025, I do not test or change the water in the crystallization dishes.  Given the tiny biomass and the presence of healthy algae, the possibility of waste nitrogen or phosphorous becoming a problem seems slim.  Maybe they need to have their water changed to get rid of chemical secreted by the algae?

With finals almost over, I can give some thought to how to separate the variables and get past the roadblock.