This Sea Cabbage Kelp is the longest we have found of its type. See Amy's feet in the bottom of the photo to get a sense of its size. They can grow to be about 5 feet (1.5 m) long and this one was just about that long. They are actually algae, brown algae to be specific.
Clue #1 This thing gets its energy from the sun.
Clue #2 It lives in and below the intertidal zone.
Clue #3 Chitons like to eat it.