![]() Eubacteria are important photosynthetizers in both oceanic and terrestrial ecosystems, and while some archaea are phototrophic, none are known to utilise oxygen-evolving photosynthesis. They include photoautotrophs from a variety of groups. Algae encompass a diverse range of organisms, ranging from single floating cells to attached seaweeds. In a reversal of the pattern on land, in the oceans, almost all photosynthesis is performed by algae and cyanobacteria, with a small fraction contributed by vascular plants and other groups. The term division has been traditionally used instead of phylum when discussing primary producers, although the International Code of Nomenclature for algae, fungi, and plants now accepts the terms as equivalent. They stabilize coastal areas and can provide habitats for marine animals. In addition, primary producers are influential in the global carbon and water cycles. The oxygen released as a by-product of photosynthesis is needed by nearly all living things to carry out cellular respiration. The principal marine primary producers are cyanobacteria, algae and marine plants. : 1242 Marine primary producers are important because they underpin almost all marine animal life by generating most of the oxygen and food that provide other organisms with the chemical energy they need to exist. This process uses energy from sunlight to convert water and carbon dioxide : 186–187 into sugars that can be used both as a source of chemical energy and of organic molecules that are used in the structural components of cells. However, most marine primary production comes from organisms which use photosynthesis on the carbon dioxide dissolved in the water. Some marine primary producers are specialised bacteria and archaea which are chemotrophs, making their own food by gathering around hydrothermal vents and cold seeps and using chemosynthesis. This means primary producers become the starting point in the food chain for heterotroph organisms that do eat other organisms. Primary producers are the autotroph organisms that make their own food instead of eating other organisms. In addition, some seagrasses, like seaweeds, can be found at depths up to 50 metres on both soft and hard bottoms of the continental shelf. These are found along coasts in intertidal regions and in the brackish water of estuaries. Later in the Cretaceous some of these land plants returned to the sea as mangroves and seagrasses. These algae then invaded the land and started evolving into the land plants we know today. Back in the Silurian, some phytoplankton evolved into red, brown and green algae. Some seaweeds drift with plankton in the sunlit surface waters ( epipelagic zone) of the open ocean. Seaweeds are found along coastal areas, living on the floor of continental shelves and washed up in intertidal zones. Marine algae includes the largely invisible and often unicellular microalgae, which together with cyanobacteria form the ocean phytoplankton, as well as the larger, more visible and complex multicellular macroalgae commonly called seaweed. Globally the ocean and the land each produce about the same amount of primary production, but in the ocean primary production comes mainly from cyanobacteria and algae, while on land it comes mainly from vascular plants. Primary production in the ocean can be contrasted with primary production on land. Some marine primary producers are also ecosystem engineers which change the environment and provide habitats for other marine life. Marine primary producers underpin almost all marine animal life by generating nearly all of the oxygen and food marine animals need to exist. Together these form the principal primary producers at the base of the ocean food chain and produce half of the world's oxygen. Most marine primary production is generated by a diverse collection of marine microorganisms called algae and cyanobacteria. The organisms responsible for primary production are called primary producers or autotrophs. Almost all life on Earth relies directly or indirectly on primary production. It principally occurs through the process of photosynthesis, which uses light as its source of energy, but it also occurs through chemosynthesis, which uses the oxidation or reduction of inorganic chemical compounds as its source of energy. Marine primary production is the chemical synthesis in the ocean of organic compounds from atmospheric or dissolved carbon dioxide. Green indicates where there are a lot of phytoplankton, while blue indicates where there are few phytoplankton. ![]() Ocean chlorophyll concentration as a proxy for marine primary production.
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