Coral anatomy A coral reef is the largest and most spectacular structure made by living things. The individual building blocks are tiny, and depend upon a partnership between a coral polyp and a photosynthetic "alga" (actually a dinoflagellate - a solitary, plantlike flagellate - the order Dinoflagellata includes luminescent forms, forms important in marine food chains, and forms causing red tide) of the kingdom Protista (a group of unicellular or acellular organisms comprising bacteria, protozoans, various algae and fungi, and sometimes viruses). The relationship is an example of endosymbiosis (symbiosis - the intimate living together of two dissimilar organisms in a mutually beneficial relationship; endo - within)

 

 

 

 

 

 

The Making of a Coral Reef A coralis a colony of many individual polyps. Each polyp is a coelenterate (a phylum of basically radially symmetrical invertebrate animals including the corals, sea anemones, jellyfishes, and hydroids) and contains dinoflagellates capable of photosynthesis (zooxanthellae). A polyp looks like a tiny sea anemone with tentacles and stinging cells to capture animal prey. By night, a polyp captures plankton with its tentacles. By day, the zooxanthellae photosynthesize. The polyp benefits from the photosynthate (product of photosynthesis), and the alga benefits from the nitrogenous wastes of the polyp. Without the zooxanthellae, the polyps cannot grow fast enough to build reefs. Coral can be either soft or hard (calcareous skeleton). Hard corals build reefs, creating rock out of sunlight, sea water, and minute animal prey (8 tons mile-2 day-1)

More than 65 species have been found in one reef: there are both shallow, fast-growing forms and deep, massive, slow-growing forms (living at a maximum depth of about 100 feet). The Great Barrier Reef has 350 named coral species. There is intense competition for space. Corals have a rigid pecking order. When more aggressive species recognize less aggressive forms, they send out nasty filaments that wound living coral encroaching on their space.