Centerpieces: Ship lanterns with tea candles inside next to small glass fish bowls with small shells on bottom and a goldfish in each. Those can be surrounded by large sea shells, star fish, and natural sponges.
Place Cards: Try large sand dollars with each persons name hand painted.
Sanity Center: A separate kids play table that can be covered in craft paper so they can draw on it! Each child can have a silver bucket and be labeled with each child's name on a bucket with stick-on letters. Inside buckets could be individual packets of Goldfish crackers, crayons, coloring books, gummy worms, etc. Kids probably wouldn't last long at the dinner tables!
Room Decor: Try using an actual sail from a sail boat and hang it from the ceiling acting as a canopy.
Picture Display: Try a large, fabric three paneled room divider that has the crisscrossed ribbons to hold pictures. Drape additional fishnetting over the three panels and attach color or black and white copies of pictures. Also, randomly attach some fishing lures to the netting and hopefuly snag in a starfish or