Possible Clues:

• Large brown leathery seaweed
• Plantlike growth held up by gas-filled bladders
• Seaweed source of iodine
• Part of a forest that can grow as fast as two feet a day
• Dashi flavorer
• Seaweed in a forest
• Food for a sea urchin
• Stuff in underwater forests
• Flora under the surface
• Makeup of underwater forests