Aha, it is the sand bubbler crab!

This picture was shot during our trip to Cape Tribulation, Queensland in 2009, when we took my visiting parents to the Great Barrier Reef.  That was Mr Hippo's toes, intended as, um, not so accurate scale because he got enormous toes.

I guessed it was some beach dwelling creature who created the elegant loving pattern, but only until now did I learn it was the sand bubbler crab!  I have to admit, I have never thought about the possibility of a crab being an artist...

I was extremely lucky to capture the heart-shaped pattern before it disappeared in the next rising tide. The crabs scour the sand for food, forming it into inflated pellets.  Comparing to other artworks we saw, this pattern was rather small.  So it was probably just a byproduct of an afternoon tea ;)