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The three basic ways in which organisms get food are as producers, consumers, and decomposers. Producers are typically plants or algae. Plants and algae do not usually eat other organisms, but pull nutrients from the soil or the ocean and manufacture their own food using photosynthesis. For this reason, they are called primary producers
All eukaryotes except for green plants and algae are unable to manufacture their own food: They obtain food from other organisms. This mode of nutrition is also known as heterotrophic nutrition . All heterotrophs (except blood and gut parasites ) have to convert solid food into soluble compounds which are capable of being absorbed (digestion).
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 pelagic food web, showing the central involvement of marine microorganisms in how the ocean imports nutrients from and then exports them back to the atmosphere and ocean floor. A marine food web is a food web of marine life. At the base of the ocean food web are single-celled algae and other plant-like organisms known as phytoplankton.
The term refers to both flowering plants submerged in the ocean, like eelgrass, as well as larger marine algae. Generally, it is one of several groups of multicellular algae; red, green and brown. [7] They lack one common multicellular ancestor, forming a polyphyletic group.
W. H. Harvey (1811–1866) and Lamouroux (1813) [34] were the first to divide macroscopic algae into four divisions based on their pigmentation. This is the first use of a biochemical criterion in plant systematics. Harvey's four divisions are: red algae (Rhodospermae), brown algae (Melanospermae), green algae (Chlorospermae), and Diatomaceae ...
Algae also use chlorophyll, but various other pigments are present, such as phycocyanin, carotenes, and xanthophylls in green algae, phycoerythrin in red algae (rhodophytes) and fucoxanthin in brown algae and diatoms resulting in a wide variety of colors. These pigments are embedded in plants and algae in complexes called antenna proteins.
Grazing differs from predation because the organism being grazed upon may not be killed. It differs from parasitism because the two organisms live together in a constant state of physical externality (i.e., low intimacy). [2] [page needed] Water animals that feed by rasping algae and other micro-organisms from stones are called grazers ...