Plant
Algae comprise several different groups of organisms which produce food by photosynthesis and thus have traditionally been included in the plant kingdom. The seaweeds range from large multicellular algae to single-celled organisms and are classified into three groups, the brown, red and green algae. There is good evidence that the brown algae evolved independently from the others, from non-photosynthetic ancestors that formed endosymbiotic relationships with red algae rather than from cyanobacteria, and they are no longer classified as plants as defined here.
Sea foam
The composition of sea foam is generally a mixture of decomposed organic materials, including zooplankton, phytoplankton, algae (including diatoms), bacteria, fungi, protozoans, and vascular plant detritus, though each occurrence of sea foam varies in its specific contents. In some areas, sea foam is found to be made up of primarily protein, dominant in both fresh and old foam, as well as lipids and carbohydrates. The high protein and low carbohydrate concentration suggest that sugars originally present in the surrounding mucilage created by algae or plant matter has been quickly consumed by bacteria. Additional research has shown that a small fraction of the dry weight in sea foam is organic carbon, which contains phenolics, sugars, amino sugars, and amino acids. In the Bay of Fundy, high mortality rates of an abundant tube-dwelling amphipod ("Corophium volutator)" by natural die-offs as well as predation by migrating seabirds contributed to amino sugars released in the surrounding environment and thus, in sea foam.