If you’ve been to the lab with me recently, you may have noticed my love affair with our visiting Frosted nudibranch friend*. I know it as Geoffrey.
So, I was very excited to be given the opportunity to learn a bit more about our happy little underwater buddy for this blog, because how can you not be enthused about critters that look like underwater hedgehogs?
Frosted, White, or Alabaster nudibranchs (Dirona albolineata) are fairly common in the subtidal zone from Alaska to California. In the San Juans, they can be found to depths of 60 meters in very high densities (up to 5 per square meter). They can be any color from clear to greenish to peach, but always have white lining their frontal veil and cerata. These cerata are shed for defense, like a chameleon’s tail (Geoffrey here isn’t looking too hot in this picture, probably due to all the recent handling). This is obviously a defense mechanism to distract predators, but Dirona may also have chemical defenses. Interestingly, as they don’t have branches of their digestive tracts in their cerata, they are unable to store nematocysts like other nudibranchs. They don’t seem to be very well-studied little guys, and the studies that do exist mainly concern their diet and anatomy, so that’s what I’ll explore here.
Geoffreys–sorry, Dirona–eat ANYTHING: hydroids, ectoprocts, small crustaceans, sponges, barnacles, diatoms, coralline algae, detritus…anything. However, it prefers snails, so if you’re feeling kind, feel free to give it a tasty snack. It will crawl rapidly and randomly over the substratum, using its frontal veil as a chemoreceptor. When it encounters a food item, it will hold the tasty morsel between its lips and ridiculously strong jaws, which will attempt to crush it. If successful, the crushed shell is swallowed, tasty bits digested, and shell compacted and rapidly pooped out in a pile of mucus. Here’s the kicker: Geoffreys eat up to 25% of their dry body weight per day. That would be like an average human eating 40 pounds of food…160 quarter pounders…icky.
References: Robilliard, G.A. (1971) Predation by the nudibranch Dirona albolineata on three species of prosobranchs. Pacific Science, 25: 429-435.
*Please ignore the blatant anthropomorphising in this post. It’s just going to happen.