Thisby is an island, but it's hardly isolated in the "no man is an island" sense. At times, it feels like a baby being cradled in the love arms of the sea. On a few occasions the sea is quoted as saying "shhhhhhhh, shhhhhhhh" (61.32) like before the races begin.
However, the sea isn't always a nurturing mother. After all, it spits out carnivorous horses faster than Heidi Klum shoots out kids. And Puck says at one point "if the sea were my mother, I'd rather have been an orphan" (21.3). The irony here, of course, is that Puck is an orphan because of the sea. Water horses ate her parents is Thisby's version of dingoes eating babies.