Coral and their Symbiotic Algae

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Coral and algae participate in a mutually symbiotic relationship that has benefitted corals in physiological and ecological ways. Algae, which are dinoflagellate endosymbionts,  provide corals with inorganic nutrients and carry out photosynthetic processes.  Photosynthesis is a very important physio-chemical process since it supplies corals with glucose, glycerol, and amino acids. Corals use these nutrients to make protein, fat, carbohydrates, and calcium carbonate.  Because of changes in seawater chemistry, corals have become stressed due to the decline in pH and carbonate ions and increase in carbonic acid, hydrogen ions, and bicarbonate. Because of these environmental changes, corals are using more energy to carry out calcification and are competing with the increasing effects of ocean acidification. Current research has shown that heterotrophic feeding can be a solution to counteract ocean acidification. By increasing heterotrophic feeding, this could provide corals with more energy to expend on calcification.

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The algae likewise benefit by taking the corals' nitrogenous waste and carbon dioxide in order to carry out photosynthesis. Corals provide shelter to algae, where the algae live on the outer epidermis cells of corals. Zooxanthellae thrive through this symbiotic relationship and their sign of good health is reflected through the beautiful colors on stony corals. Unfortunately, when coral polyps become stressed, algae is ejected from the outer epidermis and the corals will turn white.