Nudibranches in Refugium

IC Casey

Premium Member
So, I have a newly set-up AIO 40g aquarium. Started with dry rock, bagged live sand, and one piece of cured live rock from the LFS.About a month in, I added a refugium, which included some chaeto. In about two weeks, I noticed that I had a ton of small nudibranches hanging out, squirming along the chaeto. Small, yellow-brown guys. I'll try and get a good picture later.Now, without positive identification, I have a couple of guesses that they're either softy-eating, aptasia-eating, or nudibranch-eating.The tank has no other life in it, outside of the microfauna, chaeto, and algae you get towards the end of the cycle at this moment.Should I just wait it out until they starve? Should I remove the chaeto and treat with manual/chemical removal? Should I gamble on whether or not they're helpful?It's going to be a soft coral/LPS lagoon-style aquarium.   
 
Just to be sure, these are nudibranchs not flatworms?  I've never seen nudis, even the bad kind, have a true population explosion.  Even if they are, you could just avoid whatever their food time of choice is until they die off, most are very specific as to what they eat.
 
Yeah, they're definitely nudibranches. Look like the ones people sell. But I'm also aware they could be softy-eating nudis that just haven't colored up because they came over as juvenile/eggs in the chaeto and haven't really had anything to eat yet.It actually already looks like the population might be dropping. Hard to tell. My guess is they're already starving out once they get out of the larval stage in the chaeto. Don't know the lifespan of these guys.My picture sucks, because of course the dude turned upright as soon as I could get close enough to snap a photo. You can make out a number of the smaller guys. There were two in there about 1/4 in. long, and the rest were tiny, but still visible. Maybe 8-10 total.View attachment 4797View attachment 4798https://www.saltwaterfish.com/product-proaquatix-berghia-nudibranch 
 
I'd throw one in a plastic shoebox with some salt water and an aiptasia.  I'd offer you some aiptasia, but I don't have any at the moment (thank goodness for that).The odds of berghia running wild in a store display seems low unless they're actively resolving a lot of aiptasia as they are $10-20 each.  IME those turn pale white after about 48 hours of no aiptasia.  I can't tell from your photos, but I would compare them to the montipora and zoa eating ones.  If you've ever seen them in person they are very different.I'm not going to expect you to out the supplier as everyone has issues, but if those really are coral eating nudis being handed out like candy in macro algae they need to be aware and get things in order.  If you can get one to me I'll put it under a microscope at work (near 35E and Valley View).
 
I didn't see any initially in the chaeto. It was a big, dense clump and I always pull it apart to check for critters. But it's not like you can see larva or eggs or lots of the little beasties that come on things, anyway . So it was a couple of weeks I think before they appeared . Still, there would have had to be a breeding population from wherever they pull the chaeto .It came from an online vendor. 
 
Not an expert, but I would think they would have starved fairly quickly if they didn't have a food source.  Most nudis lay their eggs on whatever their food source is.
 
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