Biologically speaking, a “plant” is considered a member of the Kingdom Plantae, according to the classification system established by Whittaker in 1969 and expanded by Margulis and Schwartz in 1988. Other classification systems consider a plant differently, as an organism that releases oxygen from water during photosynthesis and contains the pigment chlorophyll. Using this latter standard, marine plants can actually be found in three different kingdoms: Monera (bacteria), Protista (algae) and Plantae (ferns and flowering plants).
Among the members of the Kingdom Monera are microscopic marine plant organisms, or phytoplankton, named from the Greek “phyton,” meaning “plant,” and “planktos,” meaning “wanderer.” Phytoplankton absorb essential nutrients in seawater through their cell walls. One such organism, Cyanobacteria, appeared to be, and was once classified with, bacteria. However, with the advances that have taken place in DNA sequencing, scientists learned the two are genetically very different. Autotrophs and heterotrophs are single-celled plants, without a cell nucleus, that comprise the base of the marine food chain. They convert ammonia and nitrogen in the water into nitrite and nitrate, useful forms that benefit other marine life. They also secrete enzymes that decompose dead marine plants and animals, converting them to inorganic nutrients. Some names of single-celled marine plants are diatoms, dinoflagellates, coccolithophorids, Prochlorococcus and Synechococcus.
Often referred to as “seaweed,” algae are from the Kingdom Protista and are what most people think of when thinking of sea plants. There are basically three classifications of algae: red algae, the most abundant with more 6,000 species; brown algae, with approximately 1,750 species; and green algae, with about 1,200 species. Red and green algae are commonly found in marine environments, while green algae can live in either marine or freshwater environments. Some interesting names of algae include bladderwrack, dabberlocks, sea whistle, spaghetti algae, green hair algae and chaeto (pronounced “kay-toe.”)
There are an estimated 50 species of seagrasses throughout the world. Unlike algae, seagrasses are flowering plants from Kingdom Plantae that grow submerged in shallow ocean waters (the mid-intertidal region, up to 50 meters deep), mostly in the tropics. Some interesting names of seagrasses include Mermaid’s Fan, Shaving Brush, Widgeon grass, paddle weed and beaked tassel weed.
- Marinebio.org: Forests of the Sea, Phytoplankton and Marine Plants
- Aquatic Connection
- Marine Botany/Clinton J. Dawes/1998
- Florida Department of Environmental Protection
- (5) Invitation to Oceanography / Paul R. Pinet / 2009
- Photo Credit Pacific Ocean image by K. Zavtrikovaite from Fotolia.com amoeba and plankton through microscope image by Allyson Ricketts from Fotolia.com Water and Seaweed image by Mr Shemp from Fotolia.com seaweed image by Kevin McGrath from Fotolia.com