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Seagrasses evolved from terrestrial plants which recolonised the ocean 70 to 100 million years ago. The name seagrass stems from the many species with long and narrow leaves, which grow by rhizome extension and often spread across large "meadows" resembling grassland; many species superficially resemble terrestrial grasses of the family Poaceae.
Seagrasses are flowering plants (angiosperms) which grow in marine environments. They evolved from terrestrial plants which migrated back into the ocean about 75 to 100 million years ago. [ 1 ] [ 2 ] In the present day they occupy the sea bottom in shallow and sheltered coastal waters anchored in sand or mud bottoms.
Marine plants can be found in intertidal zones and shallow waters, such as seagrasses like eelgrass and turtle grass, Thalassia. These plants have adapted to the high salinity of the ocean environment. Light is only able to penetrate the top 200 metres (660 ft) so this is the only part of the sea where plants can grow. [77]
The rhizomes, up to 1 cm thick, grow both horizontally (plagiotropic rhizomes), and vertically (orthotropic rhizomes). The former, thanks to the presence at the bottom of lignited roots up to 15 cm long, anchor the plant to the substrate. The latter, which increase height, have the function of combatting sanding due to continuous sedimentation.
Marine botany is the study of flowering vascular plant species and marine algae that live in shallow seawater of the open ocean and the littoral zone, along shorelines of the intertidal zone, coastal wetlands, and low-salinity brackish water of estuaries. It is a branch of marine biology and botany.
Phytoplankton are photosynthesizing microscopic protists and bacteria that inhabit the upper sunlit layer of marine and fresh water bodies of water on Earth. Paralleling plants on land, phytoplankton undertake primary production in water, [2] creating organic compounds from carbon dioxide dissolved in the water.
The organisms require nutrient-rich water with temperatures between 6 and 14 °C (43 and 57 °F). They are known for their high growth rate—the genera Macrocystis and Nereocystis can grow as fast as half a metre a day (that is, about 20 inches a day), ultimately reaching 30 to 80 metres (100 to 260 ft). [7]
It can reach 60 m (200 ft) in length and grow as rapidly as 50 cm (20 in) a day. [51] According to one study, covering 9% of the world's oceans with kelp forests could produce "sufficient biomethane to replace all of today's needs in fossil fuel energy, while removing 53 billion tons of CO 2 per year from the atmosphere, restoring pre ...