Make scuba masks for your guests to wear. Cut 1-inch wide, oval-shaped borders out of poster board or other heavy paper. To make the lens, tape clear cellophane behind them. Attach a piece of elastic to each side of the masks so they can be worn. Create a treasure chest out of a large shoebox. Cover the box with brown construction paper and pieces of gold foil or glitter paint. Fill it with shells, craft jewels, plastic necklaces and plastic gold coins. Wrap Styrofoam rings with red ribbon to make life preservers. Hang them around the party room, or hang them from the back of each chair.
Use plastic blue table cloths to cover the tables, and decorate it with clean sand, sea shells, beach glass and plastic jewels. Use any ocean-life toys as table toppers or centerpieces. Make shark and fish shapes from construction paper, hang them from blue and green streamers and suspend them from the walls and ceilings. Paint triangle shaped pieces of Styrofoam gray, and put them around the house to give the illusion of shark fins.
Make "sea water" by mixing apple juice with blue food coloring. For an extra touch, add plastic aquarium plants to the pitcher. Serve "shark bite" sandwiches. Cut jagged edges out of the corner of each sandwich to resemble the bite of a shark. Make shark shaped sugar cookies using cookie cutters in the shape of a shark. To make a shark cake, bake a rectangular shaped cake and a square shaped cake. Cut a triangle shape from the square, and put it on top of the rectangular cake to make a shark fin. If the fin will not stand on its own, use a wooden skewer to keep it stable. Frost the cake with blue frosting, and the fin with gray. Add gummy fish and sharks. Make ice cream octopuses. Put eight licorice whips on each plate, and top with two scoops of ice cream, one larger then the other.; Use icing or candy to give them each a face.