Related Clues:

• Stonewort, e.g.
• Marine ___
• Simple organism
• Chlorophyta bit
• Foot of a food chain
• Pool problem
• Low life?
• Microscopic organism
• Tiny organism
• Bit of plankton
• Bit of ocean flora
• Sea lettuce, for one
• Morsel for a sea snail
• Snack for a surgeonfish
• Aquarium dweller