Quick & easy escort cards! Just print the guest's name on a clear label, stick it onto a cardstock shape in the color of your choice, hot glue it onto one end of a toothpick (or something similar), and stick the other end into a Hershey's Kiss! Arrange on a table and voila, inexpensive (but totally delicious) escort cards!
Instead of numbers to assign guests their tables, use names of seashells. Each type of shell represents a different table. Arrange seating cards and shells on aqua fabric to give the impression of water. On each table, display a card with the shell's name, or fill a bowl with those shells as a centerpiece.