You can also press seaweed just as you would flowers. Here's how:
Fill the pan with water and place the heavy paper in the pan. Then place the seaweed on top of the paper and carefully lift out the paper and seaweed. (You can also put the paper in an empty pan, and use a turkey baster full of water to wash the seaweed into a natural configuration.)
Next, lay the wet paper on several layers of newspaper. Cover the caper and seaweed with wax paper or thin plastic film and use the waterproof marking pen to note on the paper or film the date and location that the seaweed was found, as well as the type of seaweed. Repeat this process with other seaweeds, placing them on top of the first. Then you can move the whole pile to a flat place and put some weight, like books or a rug, on top. Change the newspapers and wax paper daily (to prevent molding) until the seaweed is dry. Some seaweeds contain a natural adhesive that will keep them stuck to the paper--others may need to be mounted with some glue.
(Adapted from Nature With Children of All Ages, by Edith A. Sisson.)