what can I expect so far as survivability
We have not had a lot of surviving hatchlings of any species (many are small egged species and that nut has not been cracked so survival has been 0 across the board).
When we have had O.mercatoris hatchlings to survive 4-5 seems to be a magic guestimate, regardless of the number of hatched eggs. This is from a very small sampling size but as a hobbiest, I will throw out the numbers I remember without peer review
If you can find it, I highly recommend frozen Cyclop-eeze twice a day, preferably fed to a few grouped with shells in breeder nets. Hermits removed from their shells (tough to do and they are too large for the first few critical weeks), chopped up (smaller than mantle size) mysis or shore shrimp (table shrimp appears to be too tough until they are adults) and any kind of pods you can keep with them along with water flow (I think water flow is important but others think it is overrated). I turned off the power head while feeding but left it blowing through the nets the rest of the time.
They are a bit tricky to collect. A turkey baster works but getting the hang of sucking them off the wall (they will look like unfed white ticks) takes patience. Getting them OUT of the turkey baster can also be a challenge as they are born with functioning suckers. Try not to expose them to air in the collection process.
Very cool that you can see them moving, I have hatched out 3 broods now (2 mercs and 1 O.briearus) and never saw movement in the eggs (I never saw any of the merc eggs because the females used a barnacle shell to brood them and kept the entrance well covered). I did see chromatophore changes with the O.briareus.
You will definitely lose some of them and if you could collect them (often they will just disappear) and put them in alcohol and send me a couple, the timing is perfect for a photo project I am trying to set up comparing hatchlings from the species we normally see. I have O.briareus from my own brood, a pair of O. hummelincki from LMecher, Sarah has promised 3 bimacs she has collected and Thales is sending some O. vulgaris. I was lamenting not having access to O. mercatoris earlier in the evening. Please let me know if you would be willing to send them (again, I know you may not ever see the ones that die) and I will hold off a bit longer on attempting my photo comparison.
