I've have this urchin from ⅛ of an in. It's now 2 golf balls in dia.
It went through a rough patch I guess where it's were all very short and never knew why but for high nitrates, 40+.
But since going to NSW and getting no3 down below 20 his spines are long again. Amazes me the caves it can get into and how much it can direct its spines. It loves nori. I'm sure it tells me when it's hungry and comes to the surface for a feed. Maybe my imagination?
One of my favorite critters

It went through a rough patch I guess where it's were all very short and never knew why but for high nitrates, 40+.
But since going to NSW and getting no3 down below 20 his spines are long again. Amazes me the caves it can get into and how much it can direct its spines. It loves nori. I'm sure it tells me when it's hungry and comes to the surface for a feed. Maybe my imagination?
One of my favorite critters


