Interesting way Lettuce slug is eating algae

[Pszemol]

I have one Elysia crispata in my tank and I was always curious in how this boneless, soft animal consumes algae... I have never seen it on the glass scraping algae with its spatula like all other, regular snails do (i.e. Astrea, Nerite).

Saturday evening I caught it near the side glass, at the patch of green hair algae (Debresia). So I run for my stamp loupe (magnifier glass) and started staring at this beautifull creature...

Finally I could observe the nature of its pearl colourfull egdes of its body: green patches gradualy become dark blue and then orange to become totaly transparent at the edge...

But back to eating: Hair algae under 10x magnification look like long tubes filled with transparent, green liquid... Lettuce slug's technique of eating algae is very interesting: It aproaches a single hair with its soft mouth and hugs it
with its lips. Then you can notice like puncturing the cell wall of the algae and it starts sucking out the green fluid from the algae. When the walls of the algae body collapse, snail fills it back with water (saliva?) and goes back to sucking... You can clearly see grean parts of algae body intermixed with
transparent or whitish saliva flowing in sucking action to the slug mouth. Sucking and refills repeat many times. It is obvious from the observation, that many hairs of the algae are connected with each other, and snail (nudi) empties 2-4 hairs at once, doing only one injection/entry... Unfortunately, Lettuce Nudibranch does not eat the whole algae, so after its feast it leaves transparent, nicely cleaned and flushed from inside completely emptied threads of algae.

I could only guess it is deadly for algae, but I had no idea how quickly algae can regenerate from this. I marked the location of this Saturdays feast so I can check it later... I have confirmed yesterday evening the algae is gone in this location. Transparent leftovers dissolved completely or got eaten by amphipods/copepods teaming in this tank.

Now I wonder - if this slug eats hair algae only it can be destined for starvation in clean tanks without hair algae... It is happy in my tank, infested with debresia, but does it eat anything else?
Do you think it is a good idea to add couple of more slugs like this one to my 30g reef infested with algae?

[zhenya]

Thanks for sharing your observations of the eating proccess Yes, this type of slugs don't have the ability to "graze" anything and what you observed is the only method available to them.They puncture cell wall and suck the fluid out and move on... I think they are able to eat some other algae as well and I had read reports of them eating some Caulerpa but I would think that they would be eating a certain specie per specie of slug, another words species specific.At least to my understanding. I always loved this slugs but never attempted to keep one becouse of fear that it would simply starve in my tanks,they are unquestionably very beautiful and peaceful.
I wish you luck and continuous growth of your Derbesia,for slug's sake

[Ninong]

I have one Elysia crispata in my tank and I was always curious in how this boneless, soft animal consumes algae... I have never seen it on the glass scraping algae with its spatula like all other, regular snails do (i.e. Astrea, Nerite).

I observed my Elysia crispata (4 specimens) on the glass numerous times using a handheld magnifying glass but they passed right over the film algae without actually eating it. Unfortunately it turned out that I did not have any Derbesia spp. algae in my aquarium.

But back to eating: Hair algae under 10x magnification look like long tubes filled with transparent, green liquid...

Alf J. Nilsen has some really neat pictures of Derbesia at 10x, 100x and even 1000x magnification in this article that covers Derbesia in detail: http://www.advancedaquarist.com/issu...02/feature.htm

Lettuce slug's technique of eating algae is very interesting: It aproaches a single hair with its soft mouth and hugs it
with its lips. Then you can notice like puncturing the cell wall of the algae and it starts sucking out the green fluid from the algae.

Yes, that's how they do it. They suck out the chloroplasts which they store in their bodies. These cholorplasts remain viable for I believe a couple of weeks photosynthesizing away, providing solar powered energy to the lettuce sea slug.

Now I wonder - if this slug eats hair algae only it can be destined for starvation in clean tanks without hair algae... It is happy in my tank, infested with debresia, but does it eat anything else?

My four specimens survived for a few months but gradually wasted away. I am not sure if I had any small patches of Derbesia that I just couldn't see or not. I am not sure if they ate anything or not. I did note that they retained their green coloration during the time they were in my tank which leads me to believe they may have been eating something. I have seen specimens at the LFS that were totally white with virtually no green coloration at all. These specimens were being kept in small cubicles with virtually no light other than ambient room light. I believe their chloroplasts had "expired" and they would need to be provided with a source of Derbesia or other suitable algae to "recharge their batteries."

The four specimens that I purchased from www.reeftopia.com were all a healthy green color and about 1.5"-2" long when I got them. They were collected in the Florida Keys. I am not sure exactly what Elysia crispata eats. There are anecdotal reports from fellow hobbyists that it consumes Derbesia spp. and possibly Bryopsis spp. in home aquaria and there are observations reported in the scientific literature that it eats certain species of Caulerpa. Incidentally, the description of its Caulerpa eating technique is exactly the same as you observed with your hair algae.