Robyn talked about this song on the promo record SPECTRE, on which he explains each of the songs on RESPECT:

"I think it's about the power inside a woman. It's lunar. It's tidal.
It's just as the menstrual cycle is linked, amazingly enough, to the
passage of the moon, as are, I think, the activities of crabs. And I've
never understood why a full moon is powerful, because life on earth has
evolved with the moon. There is now a moon inside of us. If a woman
went off to Alpha Centauri or something like that she would still
menstruate in twenty-eight day cycles, at least to begin with. And
probably if you took a bunch of crabs and put them on Pluto or
something in a huge salt-water tank, they would initially act in
synch with the way the moon affected crabs on earth. So we've got that
lunar element inside of us, and I specifically link it with ... this
particular song has to do with passion, if you like -- the way quite
unexpected feelings can come up in people, just as the sea has all kind
of moods. The sea can caress you; the sea can break your neck. The
sea can be treacherous; the sea can buoy you up and keep there; the sea
can pull you down and finish you forever. The sea is your mother; the
sea is potentially your assassin. We supposedly come out of the sea.
Maybe if the word ever, sort of, chokes on its own vomit, the sea will
be the last place to be terminally polluted. There must be huge great
things down there, the size of cathedrals, kind of, buried feelings,
right at the bottom where we can't see. I think this is all just
related to the moon inside, as the hidden, the unexplained, the
uncontrollable forces of the sea, which again are controlled by the
moon."