A worldwide community photographing and learning about wildlife
Carcinus maenas
I found it all curled up like this, so I thought it might be dead. However, after nudging it, it moved a bit. I think maybe a seagull or something else might have scared it. I put it closer to the water and it seemed to move a little more
Low tide at a muddy/sandy beach
Looking at your third picture of its abdomen, this is a male green crab, due to the triangular shape (females are more rounded to allow them to hold their eggs).