Among the photosynthetic organisms inhabiting our planet, phytoplankton (microalgae, including cyanobacteria) represents only 1%, but:
🌊 Their ecological role in oceans is essential on Earth because they are responsible for 40 to 50% of total primary production.
🍃 Primary production consists of the conversion of CO2 into organic matter, a process carried out through photosynthesis.
🔅 Carbon fixation by phytoplankton during photosynthesis is estimated between 45 and 50 gigatonnes at global scale.
🐠 Phytoplankton is a primary organic resource, constituting the base of the marine food chain, as higher trophic levels organisms directly or indirectly depend on it.
🚀 Currently, although about 5000 species are described, the real number of microalgae species is estimated between 70,000 and 150,000 or even 1 million for the highest estimates.
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For more details, some bibliographic references:
✏️ Falkowski, P.G.: The Role of Phytoplankton Photosynthesis in Global Biogeochemical Cycles. Photosynthesis Research, 1994, doi:10.1007/BF00014586.
✏️ Falkowski, P.G.; Barber, R.T. and Smetacek, V.: Biogeochemical Controls and Feedbacks on Ocean Primary Production. Science, 1998, doi:10.1126/science.281.5374.200.
✏️ Geider, R.J. et al.: Primary Productivity of Planet Earth: Biological Determinants and Physical Constraints in Terrestrial and Aquatic Habitats. Global Change Biology, 2001, doi:10.1046/j.1365-2486.2001.00448.x.
✏️ Azam, F. and Malfatti, F. Microbial Structuring of Marine Ecosystems. Nature Reviews Microbiology, 2007, doi:10.1038/nrmicro1747.
✏️ de Vargas, C. et al.: Eukaryotic Plankton Diversity in the Sunlit Ocean. Science, 2015, doi:10.1126/science.1261605.