What happens to shared photos when i delete them locally? I am running out of space on my 16 GB iphone 6 (shocker.)

I have about 400 family photos that i've taken, and added to a shared album.  All of these photos are stored locally on my iPhone. 

If i remove any of those photos from my phone to free up space, are they also removed from the shared album?  (that would be bad.)

More generally: what are the semantics of shared photos? are they copies? symlinks? 

Settings: 


General>Icloud>Photos


ICloud photo library is on
optimize phone storage is checked
upload to my photo stream is on
icloud photo sharing is on.



I have backups and syncs to my macbook on a fairly routine basis, and i'm also using google photos specifically for photo backup independent of any of the above settings.
Removing photos from your Camera Roll will not remove them from Shared Albums. It will, however, remove them from iCloud Photo Library, both in iCloud itself and all of your devices.

If you have iCloud Photo Library turned on and the Optimize Phone Storage setting enabled, there's no way to further reduce the amount of storage taken by photos in your camera roll other than simply deleting them (again, subject to the caveat in the first paragraph).

Deleting photos using Photos.app should not affect their storage in the Google Photos cloud. (Deleting them with Google Photos will cause them to be removed from the Google Photos cloud.)