Seaweed
"Seaweed" is a colloquial term and lacks a formal definition. A seaweed may belong to one of several groups of multicellular algae: the red algae, green algae, and brown algae. As these three groups do not have a common multicellular ancestor, the seaweed are in a polyphyletic group. In addition, some tuft-forming bluegreen algae (Cyanobacteria) are sometimes considered to be seaweed.
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.