1. Primary Producers

Composite image showing the global distribution of photosynthesis, including both oceanic phytoplankton and terrestrial vegetation. Dark red and blue-green indicate regions of high photosynthetic activity in the ocean and on land, respectively. https://handwiki.org/wiki/index.php?curid=1828342

Primary producers are the autotroph organisms that make their own food instead of eating other organisms. This means primary producers become the starting point in the food chain for heterotroph organisms that do eat other organisms. 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. However most marine primary production comes from organisms which use photosynthesis on the carbon dioxide dissolved in the water. This process uses energy from sunlight to convert water and carbon dioxide^{[1]: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.^[1]: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.

The principal marine primary producers are cyanobacteria, algae and marine plants. The oxygen released as a by-product of photosynthesis is needed by nearly all living things to carry out cellular respiration. In addition, primary producers are influential in the global carbon and water cycles. They stabilize coastal areas and can provide habitats for marine animals. 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.^[2]

1.1. Cyanobacteria

Cyanobacteria from a microbial mat. Cyanobacteria were the first organisms to release oxygen via photosynthesis. https://handwiki.org/wiki/index.php?curid=1610286

Cyanobacteria are a phylum (division) of bacteria which range from unicellular to filamentous and include colonial species. They are found almost everywhere on earth: in damp soil, in both freshwater and marine environments, and even on Antarctic rocks.^[3] In particular, some species occur as drifting cells floating in the ocean, and as such were amongst the first of the phytoplankton.

The first primary producers that used photosynthesis were oceanic cyanobacteria about 2.3 billion years ago.^[4][5] The release of molecular oxygen by cyanobacteria as a by-product of photosynthesis induced global changes in the Earth's environment. Because oxygen was toxic to most life on Earth at the time, this led to the near-extinction of oxygen-intolerant organisms, a dramatic change which redirected the evolution of the major animal and plant species.^[6]

Prochlorococcus marinus https://handwiki.org/wiki/index.php?curid=1406545

The tiny marine cyanobacterium Prochlorococcus, discovered in 1986, forms today part of the base of the ocean food chain and accounts for more than half the photosynthesis of the open ocean^[7] and an estimated 20% of the oxygen in the Earth's atmosphere.^[8] It is possibly the most plentiful genus on Earth: a single millilitre of surface seawater may contain 100,000 cells or more.^[9]

Originally, biologists thought cyanobacteria was algae, and referred to it as "blue-green algae". The more recent view is that cyanobacteria is a bacteria, and hence is not even in the same Kingdom as algae. Most authorities exclude all prokaryotes, and hence cyanobacteria from the definition of algae.^[10][11]

2. Marine Algae

Algae is an informal term for a widespread and diverse group of photosynthetic eukaryotic organisms which are not necessarily closely related and are thus polyphyletic. Unlike higher plants, algae lack roots, stems, or leaves. Marine algae mainly fall into five groups: green algae, red algae, brown algae, diatoms and dinoflagellates. There is also a phylum of unicellular flagellates called euglenophytes. However, these have few marine members.

2.1. Green Algae

Green algae live most of their lives as single cells or are filamentous, while others form colonies made up from long chains of cells, or are highly differentiated macroscopic seaweeds. They form an informal group containing about 8,000 recognized species.^[12]

2.2. Red Algae

Modern red algae are mostly multicellular with differentiated cells and include many notable seaweeds.^[13][14] As coralline algae, they play an important role in the ecology of coral reefs. They form a (disputed) phylum containing about 7,000 recognized species.^[13]

Cyanidiophyceae colony, a class of unicellular red algae https://handwiki.org/wiki/index.php?curid=1780293

The seaweed Porphyra umbilicalis. https://handwiki.org/wiki/index.php?curid=1124931

2.3. Brown Algae

Brown algae are mostly multicellular and include many seaweeds, including kelp. They form a class containing about 2,000 recognized species.^[15]

2.4. Diatoms

Diatoms are one of the most common types of phytoplankton. https://handwiki.org/wiki/index.php?curid=1596881

They are a major algae group generating about 20% of world oxygen production.^[16] https://handwiki.org/wiki/index.php?curid=1747164

Diatoms have glass like cell walls called frustules which are made of silica.^[17] https://handwiki.org/wiki/index.php?curid=1735075

2.5. Dinoflagellate

Dinoflagellates. https://handwiki.org/wiki/index.php?curid=1355933

Euglena mutabilis, a photosynthetic flagellate. https://handwiki.org/wiki/index.php?curid=1834299

2.6. Microalgae

Algae can also be classified by size as microalgae or macroalgae. Microalgae are the microscopic types of algae, not visible to the naked eye. They are mostly unicellular species which exist as individuals or in chains or groups, though some are multicellular. Microalgae are important components of the marine protists, as well as the marine phytoplankton. They are very diverse. It has been estimated there are 200,000-800,000 species of which about 50,000 species have been described.^[18] Depending on the species, their sizes range from a few micrometers (µm) to a few hundred micrometers. They are specially adapted to an environment dominated by viscous forces.

• Microalgae

Single-celled alga, Gephyrocapsa oceanica. https://handwiki.org/wiki/index.php?curid=1222090

The coccolithophore Emiliania huxleyi. https://handwiki.org/wiki/index.php?curid=1576044

Algae bloom of Emiliania huxleyi off the southern coast of England. https://handwiki.org/wiki/index.php?curid=1876970

Zooxanthellae is a photosynthetic algae that lives inside hosts like coral. https://handwiki.org/wiki/index.php?curid=1580816

A single-celled ciliate with green zoochlorellae living inside endosymbiotically. https://handwiki.org/wiki/index.php?curid=1664974

2.7. Macroalgae

Kelp forests are among the most productive ecosystems on Earth. https://handwiki.org/wiki/index.php?curid=1405698

Macroalgae are the larger, multicellular and more visible types of algae, commonly called seaweeds. Seaweeds usually grow in shallow coastal waters where they are anchored to the seafloor by a holdfast. Seaweed that becomes adrift can wash up on beaches. Kelp is a large brown seaweed that forms large underwater forests covering about 25% of the world coastlines.^[19] They are among the most productive and dynamic ecosystems on Earth.^[20] Some Sargassum seaweeds are planktonic (free-floating). Like microalgae, macroalgae (seaweeds) are technically marine protists since they are not true plants.

A seaweed is a macroscopic form of red or brown or green algae. https://handwiki.org/wiki/index.php?curid=2036993

Global distribution of kelp forests. https://handwiki.org/wiki/index.php?curid=1491508

Macroalgae

Sargassum seaweed is a brown alga with air bladders that help it float. https://handwiki.org/wiki/index.php?curid=1677090

Sargassum fish are camouflaged to live among drifting Sargassum seaweed. https://handwiki.org/wiki/index.php?curid=1609469

This unicellular bubble algae lives in tidal zones. It can have a 4 cm diameter.^[21] https://handwiki.org/wiki/index.php?curid=1666962

3. Marine Plants

Evolution of mangroves and seagrasses. https://handwiki.org/wiki/index.php?curid=1254843

Back in the Silurian, some phytoplankton evolved into red, brown and green algae. These algae then invaded the land and started evolving into the land plants we know today. Later, in the Cretaceous, some of these land plants returned to the sea as mangroves and seagrasses.^[22]

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. Plant life can also flourish in the brackish waters of estuaries, where mangroves or cordgrass or beach grass beach grass might grow.

3.1. Mangroves

Mangroves provide important nursery habitats for marine life, acting as hiding and foraging places for larval and juvenile forms of larger fish and invertebrates. Based on satellite data, the total world area of mangrove forests was estimated in 2010 as 134,257 square kilometres (51,837 sq mi).^[23][24]

Mangroves https://handwiki.org/wiki/index.php?curid=1735519

Global mangrove forests in 2000. https://handwiki.org/wiki/index.php?curid=1462142

The seagrass common eelgrass according to IUCN data. https://handwiki.org/wiki/index.php?curid=1123955

Spalding, M. (2010) World atlas of mangroves, Routledge. ISBN 9781849776608. doi:10.4324/9781849776608.

3.2. Seagrasses

Like mangroves, seagrasses provide important nursery habitats for larval and juvenile forms of larger fish and invertebrates. The total world area of seagrass meadows is more difficult to determine than mangrove forests, but was conservatively estimated in 2003 as 177,000 square kilometres (68,000 sq mi).^[25]

Seagrass meadow. https://handwiki.org/wiki/index.php?curid=1474225

Sea dragons camouflaged to look like floating seaweed live in kelp forests and seagrass meadows^[26] https://handwiki.org/wiki/index.php?curid=1089357