BIOLOGICAL NOTES
This system never stops growing and building its own foundations. When single polyps die, or entire areas are killed by predators, they leave behind an empty skeletal frame that is quickly recolonized by live polyps which, by covering the dead corals over time, gradually establish these immense constructions. Corals reproduce either by division, infinitely recreating the original template, or by releasing their seed into the water where their young, already resembling tiny jellyfish, will be born. The polyps will not swim free in the open water for long. They will move only as far as they need to find a new site to colonize. At which point they will settle and start building, drawing the elements they need to grow from the water. Once settled, the young coral polyp cannot build its skeleton alone. It needs help from another organism, called zooxanthellae. This colorful alga is capable of photosynthesis, using solar energy to create the raw material that will feed the polyp as it grows and builds its home of calcium carbonate. The polyp’s contribution to this symbiotic relationship is to protect the tiny algae in its very tissues. Over time, with their ability to constantly produce living material, the corals have attracted vast communities to their reefs, of a diversity fit to rival that of any other living ecosystem on the planet. Around the coral reef, brightly colored fish swim proudly in pairs or in shoals. Above a sleeping turtle, Carangidae move in an eternal circle. Nearby, a solitary barracuda is ready to pounce, waiting for a careless fish to stray too far from its shoal. A parrotfish glides from one head
of coral to another, taking big bites that it grinds to sand between its powerful jaws. Two by two, the butterflyfish and angelfish patrol their territory, delicately nibbling away at sponges, corals, and other invertebrates. Sponges grow on the coral walls, taking in water through the countless pores that cover their bodies, filtering out nutrients, before ejecting the waste via a large central orifice. In areas where the currents bring the plankton into reach of their stinging polyps, the gorgonians proliferate. Almost every available surface of the reef is covered with corals or gorgonians, which in turn provide shelter for dozens of fish, crustaceans, and other marine creatures. Above a gorgonian, crinoids or sea lilies sift the water for nutrients. A closer look reveals minuscule shrimp and crabs, or even couples of remoras, all taking up home between the outstretched arms of crinoids, competing with them for food. When night falls, the reef’s diurnal inhabitants retreat to their caves or crevices. Angelfish and butterflyfish sleep in the midst of a sponge or a hole in the sand, their bright colors fading. In the deepening shadows, the vibrant tones of a parrotfish can still be glimpsed as it slips away into its coral cave. Immediately, it begins secreting the mucus that will cover its entire body like a cocoon, to prevent its odor from escaping and alerting the nocturnal predators that hunt by smell, like the fearsome moray eel.
Many other animals that rest during the day emerge into the
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