Does anyone noticed this behavior with Nudibranch Berghia?

[Aqua Splendor]

This morning I noticed my Nudibranch Berghia were floating on the surface of my water. They are doing well. Noticed also some of them sticking to each other like reproduction.

 

They already lay egg everywhere each week. They have TONS of food in my tank.

 

I never encounter this behavior from them before and was wondering if anyone had a similar experience.

 

I did a little water change, using water from my other small aquarium like I do time to time the night evening.

 

Pictures are the one end up in my sump.

[Tired]

I think that's pretty normal behavior for any gastropods small and light enough to crawl on the surface of the water. I haven't had berghias in a couple years, but there's a hitchhiker nudibranch in my tank currently that does this, and I've seen freshwater pond snails do the same.

[InAtTheDeepEnd]

12 hours ago, Tired said:

I think that's pretty normal behavior for any gastropods small and light enough to crawl on the surface of the water. I haven't had berghias in a couple years, but there's a hitchhiker nudibranch in my tank currently that does this, and I've seen freshwater pond snails do the same.

various marine snails will do it too. The smaller ones, anyway. I've never seen any of my brackish species do it though, weirdly. Not sure why. 

[Tired]

Weird. Do you have enough small brackish snails to reasonably expect that you'd see them doing this, if it was a thing they did? Water physics can't be that different for brackish water, particularly for something that works for either fresh or salt.

[InAtTheDeepEnd]

Yeah, some of them are small enough - there's a fair few that arent (faunus ater, a bunch of neritina species) but also some melanoides species which are pretty tiny who i'd expect to see doing it at least as juveniles.  But then again a majority of the livestock in that tank are species who actively consume biofilm; I've seen both the shrimps and the mollies skimming it off the water surface. So maybe the snails have just learnt that hanging round up there is a fast way to become a snack.