Since the first batches of eggs were laid years ago, it has been a struggle to get the babies to make the jump from hatchling to juvenile slug.  The eggs hatch a few weeks after having been laid, and the veligers rapidly make the transition to cute baby slugs.

Elysia clarki hatchling on Cladophora (?). 11/1/17

The problem was that they almost never progressed to the point of looking like miniature adults, as in the photo below.

Very small E. clarki that will ultimately grow to adulthood in Box of Slugs 2.0. Note the chloroplasts (green dots) and the rhinophores.  2/24/15

Once they had rhinophores at the front end, and chloroplasts inside, as seen above, they grew quickly to adults.  The problem was that the hatchling slugs would never eat.  They would crawl around on the algae, and appeared to try to feed, but never ingested anything and ultimately starved.

It was hard to know what was wrong, because any number of factors might prevent them from eating.  Were there issues with environmental conditions or pathogens that were preventing them from feeding?  Was it the type of algae?  Adults devour Bryopsis and a number of other algae species quite happily, but maybe baby slugs do not eat the same species.  For example, E. timida adults eat Acetabularia exclusively, but the hatchlings only eat Cladophora.  So what do baby E. clarki eat?

As described in previous posts, the E. clarki in my home tank (“Box of Slugs 2.0”) have been producing eggs at a relatively constant rate of one egg mass per week.  It was getting depressing to watch broods hatch, then starve over and over again.  I wanted to order some Cladophora (if it works for E. timida, why not E. clarki?), but Hurricane Irma had wiped out collecting in Florida for the winter.  I did try a species of algae that had taken over a local aquarist’s tank and that looked a lot like Cladophora, but the babies were not interested.

The Chemical Ecology students shamed me into contacting Skip Pierce again, which turned out to be a very positive thing for a number of reasons. I was surprised to hear that they had no trouble getting the slugs to start eating, but they had never been able to get them to lay eggs on a regular basis.

After a few emails back and forth between me, Pierce, and his collaborator Mike Middlebrooks, we realized that I might have been using the wrong species of Bryopsis.  The students had sequenced the DNA of the species that I culture here, and it is unambiguously B. pennata.  I have been using it for the simple reason that it plagues local aquarists, and was therefore the species I could obtain with some regularity.  After a few years of tweaking, I have been able to grow it sustainably, and the adult slugs grow big and strong using it as an exclusive food source.

Nonetheless, the babies might prefer B. plumosa.  The Pierce lab tried feeding hatchling E. clarki with a long list of algae, but they would only eat B. plumosa or Derbesia tenuissima (Curtis et al., 2007).  They did not try B. pennata, and I was skeptical so the hatchlings would be so picky about two similar species of algae.  Skip and Mike were relatively certain that the hatchlings would survive if they were fed B. plumosa.  It is possible that the youngsters that had survived in my tank before had found some D. tenuissima, which is a common nuisance algae in marine aquaria.

However, feeding them B. plumosa was easier said than done.  To my knowledge, there is no retail source for B. plumosa, and Irma had made it difficult for Mike Middlebrooks to collect any for himself or for me.  I even tried to collect in on the Eastern Shore of Marlyand, because it had been reported growing on hard surfaces there.  The strong currents, and turbid, cold water of the Atlantic in November made that trip something of a fool’s errand.  There were several species of Ulva easily available, but no Bryopsis to be found.

Ulva at Ocean City. 11/11/17

I finally decided to invite myself to Tampa.  Even if we could not find B. plumosa, I would be able to see the setup at the Middlebrooks lab.  My entire career has been spent with lab-reared insects, not marine molluscs, so it seemed a good idea to visit a real Elysia lab.  As it turns out, I got to visit two Elysia labs, because the Pierce lab at USF and Mike’s lab at the University of Tampa are relatively close to one another.  I spent 3 days in Tampa, talking endlessly with Mike about all things sluggy, and getting caught up on a lot of detail.  There really is not better way to learn about a field than having long, unstructured conversations about details few other people care about.

Mike Middlebrooks and Skip Pierce, in the Pierce Lab at the University of South Florida. 12/28/17

As an added bonus, Mike took me to his collection site at Sand Key Park in Clearwater, where we found abundant, dense, happy growths of B. plumosa.  We collected several large Ziploc bags full of Bryopsis, along with some Cladophora for good measure.

Bryopsis plumosa (the deep green stuff on the edge of the rock) and other algae on Jetty at Sand Park Key, 12/28/17.

That left the question of how to get some of it to Maryland.  After some discussion of shipping options, I decided to quadruple bag a batch of it, wrap it in a wetsuit, and check it on the airplane.  It survived the night in the hotel before the flight, although it started to develop a slight smell of shore drift.

Ziploc bag full of B. pennata. Clump of Cladophora in foreground. 12/28/17

After the long journey in imperfect conditions, the algae looked pretty good.

B. plumosa in Box of Slugs 2.0. 12/29/17

The good news is that, as of last week, E. clarki hatchlings have been eating B. plumosa.  Yaaay!  They seemed to be drawn strongly to the algae, and within a few days the proof was in their guts.  The youngster in the photo below has algae in her pair of digestive diverticula that run along her sides.  She is still very young, possibly after her first meal, and not much bigger than the veliger larva next to her.

Hatchling, with food in digestive diverticula. Veliger larva at left. 1/28/18

The slug below is larger (although the scales are different), and has stuffed herself full.  There are also older animals that are starting to develop rhinophores and parapodia, but they were not positioned for photographs.  So, it looks like we are finally past the hurdle of the first meal.  Assuming they avoid the predators and pathogens in the system, we should soon see some miniature versions of the adults.

Elysia clarki hatchling, full of algal cytoplasm.  1/26/18

One problem solved, but it is still unclear why the Pierce and Middlebrooks labs can’t get their slugs to lay eggs.  What’s worse is that Irma seems to have wiped out the wild E. clarki for the moment.  The good news is that I carried a clutch of eggs to Tampa when I visited, and Skip Pierce let me know that they are feeding and growing.  Some Maryland slugs have made their way back home.