These Slugs Like Salt (and Seagrass)


 Ahh the sea slugs.  I’ve known about nudibranchs and their incredibly diverse life history patterns and appearances since early on in high school marine invertebrate class.  I always thought they were pretty cute.

About two years ago I discovered Elysia subornata (photo abvoe from in my aquarium tanks that had come in with a large shipment of Caulerpa prolifera.  Most of the Elysia species members specialize in feeding upon just one or two species of Caulerpa and perhaps a few other species of green alga like Ulva or Chaetomorpha or Derbesia.  In fact for several months, whenever someone reported an unlucky outbreak of Caulerpa in their reefs, I was prone to suggesting they track down an Elysia nudi to stage an attack.

Unfortunately, Elysia species like to carpet surf or take spin cycle rides down overflows and into sumps and eventually find themselves macerated into chunks when they inevitably fall prey to the powerhead impeller blades.  Their use as Caulerpa control in reefs is patchy at best and more lucky break than a valuable method of control. 

But the genus, and the entire group of sea slugs, have the most eccentric and fantastic stories attached to them.  Several are kleptoplastic… they literally steal chloroplasts from the tissues of macroalgae (or seaweeds) that they feed upon.  If the nudibranch is on the edge of starvation they can use the chloroplasts to help them fight off death.  Feeding ecology and the overall impact this neat adaptation truly poses is still being studied.. but I find it so intriguing. 

Plus, their method of feeding sounds like something out of a horror film.  Elysia aren’t just your tame little chew and chew and chew herbivores.  They use radular teeth to rasp the surface of the algae and then peirce the cell walls and suck the cell sap out!  They’re mini green vampires!  In fact, if you ever read Goosebumps as a kid, they seriously remind me of the story of Bunnicula.. the vampire rabbit that would suck the life out of carrots and other vegetables. 

Little did I know that these green vampires don’t always prey upon macroalgae!  My seagrass-nerd-friend Howard from ReefCentral clued me into a review on sacoglassan nudibranch feeding and I discovered something rather shocking in the text.  There are two Elysia species that eat seagrasses!!

Chalk this up to learning something new everyday.  Little Elysia serca feeds on my beloved shoal grass, manatee grass, turtle grass, and star grass (Halodule, Halophila, Syringodium, and Thalassia) while its northern counterpart Elysia calutus likes to munch on eel grass (Zostera marina). 

Its a good thing these guys apparently don’t come out in plagues or we’d have even more issues to combat with seagrass management.  And just think.. we couldnt even use salt to get rid of these slugs!


One Comment to “These Slugs Like Salt (and Seagrass)”

  1. I found this cute little Caulerpa slug (Oxynoe antillarum) on one of my beach walks.