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
Foams can form following the degradation of harmful algal blooms (HABs). These are primarily composed of algal species, but can also consist of dinoflagellates and cyanobacteria. Biomass from algae in the bloom is integrated into sea foam in the sea surface microlayer. When the impacted sea foam breaks down, toxins from the algae are released into the air causing respiratory issues and occasionally initiating asthma attacks. "Phaeocystis globosa" is one algal species that is considered problematic, as observed in a study in the Netherlands. Its high biomass accumulation allows it to create large quantities of toxic foam that often wash onto beaches. "P. globosa" blooms are initiated in areas of high nutrient availability, often affiliated with coastal locations with a lot of stormwater runoff and eutrophication. Studies suggest that the development of foam is directly correlated to blooms caused by "P. globosa", despite that foam formation typically occurs approximately two weeks after the appearance of an algal bloom offshore. Organic material from "P. globosa" was observed decomposing while suspended at the sea surface, but was not observed lower in the water column. "P. globosa" is also considered a nuisance species because its large foam formations impair the public's ability to enjoy the beach.