Related Clues:

• Unwanted aquarium organism
• Iodine-rich seaweed
• Ocean algae used for food
• Some plankton
• Large brown algae
• Makeup of an underwater forest
• Makeup of underwater 'forests'
• Chlorophyll plant
• Fish food
• Seaweed that gives us iodine
• Sort of seaweed
• Seaweed used as food
• Bit of aquarium gunk
• Bit of rootless flora
• Film bit