Sponges are harvested (at least in Florida) on the protected West Coast (as in Tarpon Springs) where this movie was shot.
In the scene where Arnold Dix (Peter Graves), is waiting for Tony Petrakis (Robert Wagner), in the dark by the trees, as Tony is coming back from Thomas Rhys's (Richard Boone), house, Arnold attacks and brutally beats Tony numerous times about the face and even draws blood, so much so Tony passes out and can't get up but in the following scene where its the next morning and Tony's on the conch sailboat with Gwyneth Rhys (Terry Moore), Tony's face is completely unscathed with no cuts, bruises or even a swollen face, as he would most certainly be showing without question.
Near the beginning, when Robert Wagner and Gilbert Roland get off their boat to greet their family, you can see Gloria Gordon sneeze.