Coral expansion due to photosymbiosis

Article By:

Stolarski, Jarosław Institute of Paleobiology, Polish Academy of Sciences, Warsaw, Poland.

Last reviewed:November 2017

DOI:https://doi.org/10.1036/1097-8542.YB170023

Coral reefs proliferate in ocean waters that are oligotrophic, that is, extremely poor in nutrients. This paradox, first noted by Charles Darwin when he passed through Tahiti in 1842, was difficult to comprehend until symbiotic relationships between corals and photosynthesizing dinoflagellate algae (zooxanthellae), and the benefits of this partnership, were elucidated. Then, it became clear that the inorganic waste metabolites (for example, nitrogen and phosphorous compounds) of the animal host are the most desired food source for the symbiotic algae in such sterile environments. In turn, for the corals, the organic nutrients (for example, glycerol) fixed by algal photosynthesis are essential as respiratory substrates that support the growth of the animals (Fig. 1). Because the algal symbiosis enhances the coral host's metabolic processes, including calcification, the growth rates of symbiotic coral skeletons far exceed the ability of physical erosion and boring organisms to break them down. Consequently, rapidly formed symbiotic coral skeletal structures, conferred by the relationship with photosynthetic algae, contribute to the formation of the largest calcium carbonate bioconstructions of the world—the coral reefs. See also: Algae; Carbonate minerals; Ecological communities; Ecology; Marine ecology; Mutualism; Photosynthesis; Reef; Symbiosis

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