I have attempted to grow cacti from seeds I collected from my own cactus. Since the last time I tried this (last year), only about 5 seeds started germination and then quickly died, this time I thought I'd simply use some more seeds to increase the chance that any at all will survive.
Now unfortunately (well, actually that's a good thing, I guess) a lot of my seeds started germination so now my pots are pretty full with small cactus seedlings:
While in general it's great that so many even survived, I'm concerned that they won't have enough space (especially those in the lower pots in the image) and it will negatively affect their further growth.
Since they're so young (only a few weeks old, an individual seedling is maybe some 1-2mm), I assume I cannot transplant them without a large number of those transplanted dying. So my options are
Leave it as it is and hope it regulates itself, then transplant in a few months (?) when they're larger
manually remove some seedlings to give the rest more space
I'm not sure which of those options is better since I don't have much experience growing plants. The problem with 1. seems to be that by leaving all seedlings in one pot, maybe all will have problems growing and all will die (instead of just the weaker ones). However with removing cacti (and possibly trying to transplant them), I might damage the seedlings right next to the one I remove.
So what should I do? Is there any other option than the ones I've listed? If it's relevant, those are Mammillaria cacti (I'm almost completely sure that the top row are Mammillaria Spinosissima Pilcayensis and the rest are Mammillaria Mystax - I could provide pictures if needed).
TL;DR: If too many cactus seedlings are in the same pot, should I let them be, remove some or do something completely different?
The most similar question to mine I could find on this site is Are there too many Asiatic lilies in this pot? but I don't think it's a duplicate since seedlings might need different treatment as they're more vulnerable (hence the transplantation problem).