Wow - what a great question - great food for thought! Can the ocean here in the novel be metaphoric for the sac within our mother's body where we all begin our lives?
I'm reading it that way, and yes - I agree. For most of us I am betting that any time we are around water, we find ourselves to be more at peace than usual. Even a bathtub can provide that experience. In the novel, Janice returned to the ocean to try to find peace, and Emma throughout the novel returned to the ocean shore to hunt for the crab and find her calm center. Even Leo, at the very end of the novel, leaves little Ruby with Jill and goes off to help find Janice. Ironically, it is near the ocean that they all learn the missing pieces to the puzzle that helps them find the internal peace they all seek.