Coral Physiology

In an experiment by Thomas F. Goreau and Nora I. Goreau to further Younge’s work, radioactive Carbon 14 was given to coral. During the day, it was noted that zooxanthellae photosynthetically fixed the Carbon 14 into organic matter at a rate dependant to light intensity. It was observed that some of the organic matter then leaked from algae to coral host.

Trench and Leonard Muscatine at UCLA and David Smith at Oxford showed that the organic matter leaked in the experiment performed by Thomas F. Goreau and Nora I. Goreau includes simple compounds like glycerol, glucose, and amino acids. The coral uses these compounds for metabolic pathways, which produce energy, or the production of proteins, fats, or carbohydrates.

It is common information that metabolic reaction rates are regulated by waste product removal rates. Higher animals remove waste by specialized circulatory and excretory systems. Coelenterates use diffusion to remove insoluble waste products like carbon dioxide, phosphates, nitrates, sulfates, and ammonia. Zooxanthellae need these products for photosynthesis in their mutual relationship with corals. 

Coral polyps have 3 major sources of nutrition:  

Organic matter leaked by zooxanthellae

Prey that have been stung

Absorbing dissolved organic compounds across the body wall

Organic matter leaked by zooxanthellae:

 During the day, the symbiotic zooxanthellae make more oxygen than the coral polyp can use for respiration. Photosynthesis takes up Carbon 12 faster than Carbon 13, so compounds rich in Carbon 13, left behind, primarily make up the coral’s calcium carbonate skeleton. Using a mass spectrometer, it was determined that about 2/3 of the carbon taken up during photosynthesis and calcification processes are reused from the coral polyp’s respiratory carbon dioxide and the remaining 1/3 from seawater.

Prey that have been stung:

 Corals get plankton with stinging cells or trapping them on filaments of mucus that are then re-ingested. The coral responds chemically, extends its tentacles, and opens its mouth or sticks out mesenterial filaments. Corals generally are not active in hunting for food. Instead, they wait until food comes to it.

Corals passively catch plankton when they become stuck to the coral’s mucus. A cilia moves the plankton to the mouth, then to the pharynx and finally the coelenteron. After the food is digested in the coelenteron, it is absorbed by gastrodermal cells. Lastly, the food nutrients are distributed to all the cells in the coral.

Dissolved organic compounds across the body wall:

 James Porter from the University of Georgia has found from examining coral stomachs that corals eat tiny crustaceans and worm-like plankton. These crustaceans and plankton are those that hide in interstices of the reef during the day and come out at both sunrise and sunset.

Coral Reefs