Sign of sponge harvesting?

This looks like someone took a saw through a sponge to cut it off. Anyone have any idea what these groove marks are?

Hi,
when i see the seafan next to it, can not imagine a harvest....
Could it be marks from a waving seafan?
Looks a bit radial, but that could be a bent seafan as well.
If that goes up and down in a strong current,
it could leave sings in the sponge....

A seafan will win against most hard corals in chemical warfare....

Regards,
Wolfgang

Thanks Wolfgang. That makes a whole lot of sense when I look at the whole picture.