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Marine primary production is the chemical synthesis in the ocean of from atmospheric or dissolved carbon dioxide. 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. Almost all life on Earth relies directly or indirectly on primary production. The organisms responsible for primary production are called primary producers or .
Most marine primary production is generated by a diverse collection of marine microorganisms called algae and cyanobacteria. Together these form the principal primary producers at the base of the ocean food chain and produce half of the world's oxygen. Marine primary producers underpin almost all marine animal life by generating nearly all of the oxygen and food marine animals need to exist. Some marine primary producers are also ecosystem engineers which change the environment and provide Marine habitat for other marine life.
Primary production in the ocean can be contrasted with primary production on land. 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 .
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. Seaweeds are found along coastal areas, living on the floor of continental shelves and washed up in . Some seaweeds drift with plankton in the sunlit surface waters (epipelagic zone) of the open ocean. Back in the Silurian, some phytoplankton evolved into Red algae, Brown algae and green algae. These algae then invaded the land and started evolving into the we know today. Later in the Cretaceous some of these land plants returned to the sea as and . These are found along coasts in Intertidal zone and in the brackish water of estuaries. 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.
Marine primary production is measured as gross primary production (GPP), the total carbon fixed by photosynthesis, or as net primary production (NPP), which subtracts the carbon respired by primary producers themselves. Estimates are made using in-situ bottle incubations, satellite ocean-color observations, and global biogeochemical models. Current analyses suggest that marine NPP averages about 45–55 gigatons of carbon per year, accounting for nearly half of Earth's total primary production. This production fluctuates across regions and time scales, influenced by phenomena such as the El Niño–Southern Oscillation, monsoons, and long-term shifts in ocean circulation.
• Red = [[diatom]]s (big phytoplankton, which need silica)Opacity indicates concentration of the carbon biomass. In particular, the role of the swirls and filaments ( features) appear important in maintaining high biodiversity in the ocean. Modeled Phytoplankton Communities in the Global Ocean NASA Hyperwall, 30 September 2015. Darwin Project Massachusetts Institute of Technology.]]
• Yellow = [[flagellate]]s (other big phytoplankton)
• Green = [[prochlorococcus]] (small phytoplankton that cannot use nitrate)
• Cyan = [[synechococcus]] (other small phytoplankton)
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 , 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 (2025). 9780321543257, Pearson – Benjamin Cummings. ISBN 9780321543257 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. 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 cycle and water cycle 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.
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. Algae encompass a diverse range of organisms, ranging from single floating cells to attached seaweeds. They include photoautotrophs from a variety of groups. Bacteria are important photosynthetizers in both oceanic and terrestrial ecosystems, and while some archaea are , none are known to utilise oxygen-evolving photosynthesis. A number of are significant contributors to primary production in the ocean, including , and , and a diverse group of unicellular groups. Vascular plants are also represented in the ocean by groups such as the .
Unlike terrestrial ecosystems, the majority of primary production in the ocean is performed by free-living microorganism called phytoplankton. It has been estimated that half of the world's oxygen is produced by phytoplankton. Larger autotrophs, such as the seagrasses and macroalgae () are generally confined to the littoral zone and adjacent shallow waters, where they can attach to the underlying substrate but still be within the photic zone. There are exceptions, such as Sargassum, but the vast majority of free-floating production takes place within microscopic organisms.
The factors limiting primary production in the ocean are also very different from those on land. The availability of water, obviously, is not an issue (though its salinity can be). Similarly, temperature, while affecting metabolism rates (see Q10), ranges less widely in the ocean than on land because the heat capacity of seawater buffers temperature changes, and the formation of sea ice insulates it at lower temperatures. However, the availability of light, the source of energy for photosynthesis, and mineral nutrients, the building blocks for new growth, play crucial roles in regulating primary production in the ocean. Available Earth System Models suggest that ongoing ocean bio-geochemical changes could trigger reductions in ocean NPP between 3% and 10% of current values depending on the emissions scenario.
In 2020 researchers reported that measurements over the last two decades of primary production in the Arctic Ocean show an increase of nearly 60% due to higher concentrations of phytoplankton. They hypothesize new nutrients are flowing in from other oceans and suggest this means the Arctic Ocean may be able to support higher trophic level production and additional carbon fixation in the future.
The first primary producers that used photosynthesis were oceanic cyanobacteria about 2.3 billion years ago. 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.
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 and an estimated 20% of the oxygen in the Earth's atmosphere. It is possibly the most plentiful genus on Earth: a single millilitre of surface seawater may contain 100,000 cells or more.
Originally, biologists thought cyanobacteria was algae, and referred to it as "blue-green algae". The more recent view is that cyanobacteria are bacteria, and hence are not even in the same Kingdom as algae. Most authorities exclude all prokaryotes, and hence cyanobacteria from the definition of algae.
A chloroplast is a type of organelle known as a plastid, characterized by its two membranes and a high concentration of chlorophyll. They are highly dynamic—they circulate and are moved around within plant cells, and occasionally pinch in two to reproduce. Their behavior is strongly influenced by environmental factors like light colour and intensity. Chloroplasts, like mitochondria, contain their own DNA, which is thought to be inherited from their ancestor—a photosynthetic cyanobacterium that was symbiogenesis by an early eukaryotic cell. Chloroplasts cannot be made by the plant cell and must be inherited by each daughter cell during cell division.
Most chloroplasts can probably be traced back to a single endosymbiotic event, when a cyanobacterium was engulfed by the eukaryote. Despite this, chloroplasts can be found in an extremely wide set of organisms, some not even directly related to each other—a consequence of many secondary and even tertiary endosymbiotic events.
In 2000 a team of microbiologists led by Edward DeLong made a crucial discovery in the understanding of the marine carbon and energy cycles. They discovered a gene in several species of bacteria responsible for production of the protein rhodopsin, previously unheard of in bacteria. These proteins found in the cell membranes are capable of converting light energy to biochemical energy due to a change in configuration of the rhodopsin molecule as sunlight strikes it, causing the pumping of a proton from inside out and a subsequent inflow that generates the energy. Bacteria with Batteries, Popular Science, January 2001, Page 55. The archaeal-like rhodopsins have subsequently been found among different taxa, protists as well as in bacteria and archaea, though they are rare in complex multicellular organisms.
Research in 2019 shows these "sun-snatching bacteria" are more widespread than previously thought and could change how oceans are affected by global warming. "The findings break from the traditional interpretation of marine ecology found in textbooks, which states that nearly all sunlight in the ocean is captured by chlorophyll in algae. Instead, rhodopsin-equipped bacteria function like hybrid cars, powered by organic matter when available—as most bacteria are—and by sunlight when nutrients are scarce." A tiny marine microbe could play a big role in climate change University of Southern California, Press Room, 8 August 2019.
There is an astrobiology conjecture called the Purple Earth hypothesis which surmises that original life forms on Earth were retinal-based rather than chlorophyll-based, which would have made the Earth appear purple instead of green.
are almost exclusively marine and are found in large numbers throughout the Photic zone of the ocean. They have calcium carbonate plates (or scales) of uncertain function called , which are important microfossils. Coccolithophores are of interest to those studying global climate change because as ocean acidity increases, their coccoliths may become even more important as a carbon sink. The most abundant species of coccolithophore, Emiliania huxleyi is an ubiquitous component of the plankton base in marine food webs. Management strategies are being employed to prevent eutrophication-related coccolithophore blooms, as these blooms lead to a decrease in nutrient flow to lower levels of the ocean.
Traditionally the phylogeny of microorganisms, such as the algal groups discussed above, was inferred and their taxonomy established based on studies of morphology. However developments in molecular phylogenetics have allowed the evolutionary relationship of species to be established by analyzing their DNA and protein sequences. Many taxa, including the algal groups discussed above, are in the process of being reclassified or redefined using molecular phylogenetics. Recent developments in molecular sequencing have allowed for the recovery of directly from environmental samples and avoiding the need for culturing. This has led for example, to a rapid expansion in knowledge of the abundance and diversity of marine microorganisms. Molecular techniques such as genome-resolved metagenomics and single cell genomics are being used in combination with high throughput techniques.
Between 2009 and 2013, the Tara expedition traversed the world oceans collecting plankton and analysing them with contemporary molecular techniques. They found a huge range of previously unknown photosynthetic and mixotrophic algae.Bork, P., Bowler, C., De Vargas, C., Gorsky, G., Karsenti, E. and Wincker, P. (2015) " Tara Oceans studies plankton at planetary scale". . Among their findings were the . These organisms are generally colourless and oblong in shape, typically about 20 μm long and with two flagella. Evidence from DNA barcoding suggests diplonemids may be among the most abundant and most species-rich of all marine eukaryote groups.Faktorová, D., Dobáková, E., Peña-Diaz, P. and Lukeš, J., 2016. From simple to supercomplex: mitochondrial genomes of euglenozoan protists. F1000Research, 5. . Modified text was copied from this source, which is available under a Creative Commons Attribution 4.0 International License.De Vargas, C., Audic, S., Henry, N., Decelle, J., Mahé, F., Logares, R., Lara, E., Berney, C., Le Bescot, N., Probert, I., Carmichael, M. and 44 others (2015) "Eukaryotic plankton diversity in the sunlit ocean. Science", 348(6237): 1261605. .
The earliest land plants probably interacted with beneficial substrate microbiota that aided them in obtaining nutrients from their substrate. Furthermore, the earliest land plants had to successfully overcome a barrage of terrestrial stressors (including ultraviolet light and photosynthetically active irradiance, drought, drastic temperature shifts, etc.). They succeeded because they had the right set of traits—a mix of adaptations that were selected for in their hydro-terrestrial algal ancestors, exaptations, and the potential for co-option of a fortuitous set of genes and pathways. During the course of evolution, some members of the populations of the earliest land plants gained traits that are adaptive in terrestrial environments (such as some form of water conductance, stomata-like structures, embryos, etc.); eventually, the "hypothetical last common ancestor of land plants" emerged. From this ancestor, the extant and evolved. While the exact trait repertoire of the hypothetical last common ancestor of land plants is uncertain, it will certainly have entailed properties of Vascular plant and non-vascular plants. What is also certain is that the last common ancestor of land plants had traits of algal ancestry.
Plant life can flourish in the brackish waters of estuaries, where mangroves or cordgrass or beach grass might grow. grow in sandy shallows in the form of , line the coast in tropical and subtropical regions and Halophyte plants thrive in regularly inundated . All of these habitats are able to sequester large quantities of carbon and support a Marine biology range of larger and smaller animal life. Marine plants can be found in and shallow waters, such as like Zostera and turtle grass, Thalassia. These plants have adapted to the high salinity of the ocean environment.
Light is only able to penetrate the top so this is the only part of the sea where plants can grow. The surface layers are often deficient in biologically active nitrogen compounds. The marine nitrogen cycle consists of complex microbial transformations which include the fixation of nitrogen, its assimilation, nitrification, anammox and denitrification. Some of these processes take place in deep water so that where there is an upwelling of cold waters, and also near estuaries where land-sourced nutrients are present, plant growth is higher. This means that the most productive areas, rich in plankton and therefore also in fish, are mainly coastal.
A key unresolved question is what determines C:N:P of individual phytoplankton. Phytoplankton grows in the Epipelagic zone, where the amount of inorganic nutrients, light, and temperature vary spatially and temporally. Laboratory studies show that these fluctuations trigger responses at the cellular level, whereby cells modify resource allocation in order to adapt optimally to their ambient environment. For example, phytoplankton may alter resource allocation between the P-rich biosynthetic apparatus, N-rich light-harvesting apparatus, and C-rich energy storage reserves. Under a typical future warming scenario, the global ocean is expected to undergo changes in nutrient availability, temperature, and irradiance. These changes are likely to have profound effects on the physiology of phytoplankton, and observations show that competitive phytoplankton species can acclimate and adapt to changes in temperature, irradiance, and nutrients on decadal timescales. Numerous laboratory and field experiments have been conducted that study the relationship between the C:N:P ratio of phytoplankton and environmental drivers. It is, however, challenging to synthesize those studies and generalize the response of phytoplankton C:N:P to changes in environmental drivers. Individual studies employ different sets of statistical analyses to characterize the effects of the environmental driver(s) on elemental ratios, ranging from a simple t test to more complex mixed models, which makes interstudy comparisons challenging. In addition, since environmentally induced trait changes are driven by a combination of plasticity (acclimation), adaptation, and life history, stoichiometric responses of phytoplankton can be variable even amongst closely related species.
Meta-analysis/systematic review is a powerful statistical framework for synthesizing and integrating research results obtained from independent studies and for uncovering general trends. The seminal synthesis by Geider and La Roche in 2002, as well as the more recent work by Persson et al. in 2010, has shown that C:P and N:P could vary by up to a factor of 20 between nutrient-replete and nutrient-limited cells. These studies have also shown that the C:N ratio can be modestly plastic due to nutrient limitation. A meta-analysis study by Hillebrand et al. in 2013 highlighted the importance of growth rate in determining elemental stoichiometry and showed that both C:P and N:P ratios decrease with the increasing growth rate. In 2015, Yvon-Durocher et al. investigated the role of temperature in modulating C:N:P. Although their dataset was limited to studies conducted prior to 1996, they have shown a statistically significant relationship between C:P and temperature increase. MacIntyre et al. (2002) and Thrane et al. (2016) have shown that irradiance plays an important role in controlling optimal cellular C:N and N:P ratios. Most recently, Moreno and Martiny (2018) provided a comprehensive summary of how environmental conditions regulate cellular stoichiometry from a physiological perspective.
The elemental stoichiometry of marine phytoplankton plays a critical role in global biogeochemical cycles through its impact on nutrient cycling, secondary production, and carbon export. Although extensive laboratory experiments have been carried out over the years to assess the influence of different environmental drivers on the elemental composition of phytoplankton, a comprehensive quantitative assessment of the processes is still lacking. Here, the responses of P:C and N:C ratios of marine phytoplankton have been synthesized to five major drivers (inorganic phosphorus, inorganic nitrogen, inorganic iron, irradiance, and temperature) by a meta-analysis of experimental data across 366 experiments from 104 journal articles. These results show that the response of these ratios to changes in macronutrients is consistent across all the studies, where the increase in nutrient availability is positively related to changes in P:C and N:C ratios. The results show that eukaryotic phytoplankton are more sensitive to the changes in macronutrients compared to prokaryotes, possibly due to their larger cell size and their abilities to regulate their gene expression patterns quickly. The effect of irradiance was significant and constant across all studies, where an increase in irradiance decreased both P:C and N:C. The P:C ratio decreased significantly with warming, but the response to temperature changes was mixed depending on the culture growth mode and the growth phase at the time of harvest. Along with other oceanographic conditions of the subtropical gyres (e.g., low macronutrient availability), the elevated temperature may explain why P:C is consistently low in subtropical oceans. Iron addition did not systematically change either P:C or N:C.
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