Marine phytoplankton
Under marine phytoplankton is microscopic understands algae , the free-floating in the sea water to live. Phytoplankton feeds autotrophically and converts inorganic compounds into organic substances by means of photosynthesis , which forms the food basis of the heterotrophic living organisms (e.g. zooplankton , fish etc.). The phytoplankton is therefore the primary producer in the ocean's material cycle, producing around 75% of the world's oxygen and metabolizing roughly the same amount of carbon dioxide as the continental plants. A massive occurrence of phytoplankton is also known as algal bloom and often leads to hypoxia .
Because it depends on light for photosynthesis, phytoplankton live in the upper, euphotic zone of the sea. The algae change location with the help of ocean currents . With some algae classes, the organism can also move itself through one or more flagella . For a more extensive change of location, however, only the ocean current is to be regarded as a relevant variable. In order to counteract a sinking to aphotic depths that are no longer reached by sunlight and to reduce their sinking speed, species have also developed various strategies: They increase their form resistance , for example by developing small and flat body shapes and shells or bristles, or by reducing them their weight by preferentially storing light ions , producing gas bubbles or light fats.
The occurrence of phytoplankton is determined by the supply of nutrients, light, the mixing of the surface water with deeper layers and the density of the water. The latter, in turn, depends on the temperature and salinity. For example, in spring in mid-latitudes, a shallow, warm layer of light surface water can form that hardly mixes with the layer below. In this light-flooded water, rapid cell division, often several times a day, can lead to an explosive reproduction of diatoms. If the minerals in this water layer are used up in summer, the species composition often changes. Phytoplankton and heterotrophic zooplankton, which grow on the basis of the nutrients of dead plankton, then dominate.
It can be divided into size classes which, however, have no morphological significance. Usual divisions roughly correspond to the mesh size of the nets with which it is caught. The smallest plankton that can be caught with nets belong to the microplankton with a size range of approx. 20 µm - 200 µm. Many phytoplankton belong to the nanoplankton , whose size is 2 µm - 20 µm.
The material composition of phytoplankton can be approximated by the Redfield ratio .
Important groups of marine phytoplankton are diatoms and autrophic flagellates , including coccolithophorida and dinoflagellates , some of which are poisonous species and which can also endanger human health when algal blooms.
literature
- Carmelo R. Tomas: Identifying Marine Phytoplankton . Elsevier, 1997, ISBN 978-0-12-693018-4 .
Web links
- Genny Anderson, Rebecca Martin: Marine Plankton. In: Marine Science. November 2, 2018. Distance learning course at Clark College, Vancouver.
Individual evidence
- ^ Old theory of phytoplankton growth overturned. Federal Ministry of Education and Research , July 22, 2010, accessed on January 14, 2020 .
- ↑ Phytoplankton. Federal Ministry of Education and Research, accessed on January 14, 2020 .
- ↑ a b c Eva-Maria Nöthig: The phytoplankton at a glance . In: Gotthilf Hempel, Irmtraut Hempel, Siegrid Schiel (eds.): Fascination Marine Research . HM Hauschild, Bremen 2006, ISBN 3-89757-310-5 , p. 82-86 .
- ↑ Plankton. In: Spectrum Lexicon of Biology. Retrieved May 10, 2009 .