BigB - your concern is very touching, but fear not. I have it on good authority that the prawn, whose name is Nigel, is a specially-trained stunt prawn, and the "golf ball" you see him hit with his head is made from papier mache. This is then cut with scenes of the proper golf ball flying through the ocean. An RSPCA inspector was on hand at all times to ensure Nigel was as safe as a stunt prawn can be.
Nigel was paid handsomely for the ad, which he was delighted to be in because of the repeat fees (although Nigel is a veteran of films such as Finding Nemo and The Little Mermaid, stuntwork as a body double is surprisingly sparse for ocean-dwelling crustaceans). He hopes the money will help his family get over the loss of cousin Frank, who played his final starring role just last night, in my prawn curry. Burp. Cheers, Frank.