The Coral Reef – A General Background:


Coral Reefs usually form in shallow, tropical waters and become central to the ecosystems that they create. They are formed by creatures of the Phylum Cnidaria, which consists of ~1000 species. They are very much like sea anenomies, except in that they have a calcium carbonate skeleton which remains behind when they die, allowing for the building of the reef by many generations of polyps. (A polyp is the single building-block unit of a coral; it consists of a sac which can expand and contract, tentacles, and a mouth-slit called a stomodaeum, which leads to the larynx. Polyps can be either sexual or asexual, and among the sexual, there exist both single-gender and mixed-gender coral structures. Corals Generally need water of ~18-32°C in order to survive. They also tend to be no deeper than 150 m because they are dependant on a symbiotic relationship with algae who need sun to survive. In areas containing moving sediment, the corals are put under stress to keep their surfaces clear (in order to allow gas exchange and keep their tentacles functional). They can not live in areas exposed by low tides, and many species have trouble resisting basic mechanical breakage in turbulent waters. This being said, special considerations are needed in order to make sure that human disturbance does not cause any unfavorable conditions in healthy reefs.

Coral Reefs can be found along the entire circumference of San Cristóbal, but the most diverse and interesting reef is found at Pitt Point, on the northeastern corner of the island. This corals of this reef are Pocillopora, P. damicornis, P. elegans, Porites lobata, Pavona clavus. The ecosystem here is home to Eucidaris, Trizopagurus magnificus (hermit crab), Latiaxis (Babelomeurex)hindsii (a gastropod), the pufferfish Arothron melegris (Lacépède), and the Parrotfish Scarus ghobban, Scarus perrico, and Scarus rubroviolaceus. (pp. 39-42) <> 
Note: The Source contains annotated maps of the reef zones.<>


Source:

Glynn, Peter W., Wellington, Gerard M., Wells, John W. Corals and Coral Reefs of the Galápagos Islands. University of California Press: Berkeley, CA; 1983.