I made two 12″ cake layers with vanilla buttercream frosting for this Finding Nemo Birthday Cake. Everything on the cake is edible.
The characters are made out of fondant. The seashells are made in candy molds with colored candy melt chocolate. The fish are made of sugar (purchased from The Party Works) and I made the coral and seaweed out of piped royal icing.
After frosting the cake, I piped a small wavey look at the base then used Wilton Color Mist food coloring blue spray for an ocean look. The crumbles around the base for the sand are the Wilton turtle crunch sprinkles.
When making the seaweed and coral, after the royal icing was hard, I spray painted the colors( Wilton Color Mist spray), then glued them to the cake with additional frosting. The name plaque was also a candy mold with melted candy melt vanilla candy then piped the writing with the blue icing.
I got some of the ideas by pulling up pictures of the movie on the internet.