White spears growing in amongst macro algae

[OldRed1]

My macro algae is growing in well. As it grows, so too are these little white spears. Any idea what they are?

 

[ISpeakForTheSeas]

My guess is some kind of sponge, but I don't know for sure.

 

[ying yang]

Sponges I believe what them white spears you showing is.
Here a little zoa frag off mine ,tank lights are off so zoas shut so ideal to show you similar I got but mine stick out horizontal instead off vertical and last picture zoomed in if trace it back ,you can see goes to the main part off the sponge inbetween the zoa polyps.
Did have a vertical one on my gsp but as polyps been retracted for ages now,I moved it to top off rocks and part off gsp broke off with the sponge on but this sponge looked truly weird with spikes an all lol

 

[ying yang]

Here the other sponge on gsp I mentioned and can see the white thin part off sponge going vertical at about 3/4 into video.
I'm not sure but looks like sends out runners to anchor on in different ways and attach to rock but also seem to go out into water column either looking for more anchor points or to grab particles Idk ( don't mean the pulsating openings)