what is this all over my live rock?

I’m really new to this hobby (about 2 months) – my live rock has a bunch of these things growing on it, but they go away as soon as my reef light comes on in the morning. When I shut off the light, they stretch back out. I’ve read up and was unable to figure out what these are. My hermit crabs don’t seem to be eating them, and some of my damsels pick at them from time to time but they don’t seem to be bothered by them (yet)

Can anyone identify this?

thanks,
Mike

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