Something on my sandbed... ID?

[Vincero]

I noticed something interesting on my sandbed today. It might be nothing, but whatever it is appears to be holding pieces of sand.

It's small, red, and thorny.

Any ideas what this is? Hopefully my pictures show it clearly enough.

Thanks

 

[EdgeN]

It looks like some type of red macro algae IMO.

 

[Vincero]

Interesting. Hopefully okay to leave it in...