Calcareous algae
Calcareous algae are not closely related systematic groups ( taxa ) of either unicellular or multicellular, aquatic , photoautotrophic organisms, which deposit calcium carbonate ("carbonate of lime", CaCO 3 ) in the course of their metabolic activity. This happens either in the form of calcareous skeletons or in the form of calcareous crusts. Depending on the group, either calcite or aragonite is deposited .
The calcareous algae include some cyanobacteria (blue-green algae), the coralline red algae ( Corallinaceae ), various groups of green algae (e.g. the genus Penicillus ) as well as the coccolithophores (calcium flagellates) and the calcareous dinoflagellates (Calciodinelloideae), both groups of complex unicellular algae, which go back to a secondary endosymbiosis (the plastid in them is not primarily due to an ingested cyanobacterium, but secondarily to a red alga, of which only a few relics are preserved in the cell today, with the exception of its plastids). The green algae and chalky dinoflagellates are the only representatives that live in fresh water. Only the coccolithophores and calcareous dinoflagellates are planktonically living representatives (although many dinoflagellates do not secrete lime throughout their life, but only in certain phases of their life cycle). Both groups are mixotrophic , which means that they are not only able to feed through photosynthesis but also for heterotrophic nutrition.
Benthic calcareous algae play an important role in stabilizing (incrustation) of reefs , build some even alone reef structures (so-called pseudo reefs ) on. Planktonic calcareous algae, especially the coccolithophores, are the source of the mighty, fine-grained deep sea limestone ( "chalk" ) of the Cretaceous period .
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- Calcareous algae in the spectrum online encyclopedia of geosciences