As soon as I saw this I thought of the song in the Disney movie "The Little Mermaid" "Under the Sea". It is happy just like that song.
As for quilting you could do wavy lines across it to represent the currents in the water.
This quilting design,by Christina Cameli, also gives lots of motion.
https://www.pinterest.com/pin/192880796521828681/
According to the Pinterest link it is from this book
https://www.amazon.com/Step-Step-Fre...VFFEAMNEDBQR5N