The ecosystems that inhabit coral reef regions are filled with countless symbiotic relationships that have developed over millions of years. From the tiniest of dinoflagellates to the morays and sharks that cruise the reef, each plays its part in the maintenance of the reef ecosystem's overall health.
Dinoflagellates are tiny marine protists, of which zooxanthella are a subtype which plays a large role in coral symbiosis. These creatures take up residence inside the folds and crevices of corals. Often due to poor nutrient content in the ocean where coral reefs exist, the dinoflagellates depend on corals for protection as well as nutrients. The coral in turn must grow in low depths in shelf-like formations that allow the dinoflagellates they harbor to have enough sunlight for photosynthesis. In this manner, corals get most of their energy from the photosynthesis, and excrete waste that includes nutrients needed by the dinoflagellates.
Corals also excrete mucus on their surfaces to keep clean enough that sunlight is not obscured for their guests. This mucus is then eaten by a multitude of small fish that live in the shelter of the coral reef. Corals protect the fish from being battered by strong currents and storm strengthened waves. These fish also provide the corals and surrounding area with nutrients from their waste.
The fish that thrive on the coral mucus are hunted by predators such as moray eels, barracuda, and sharks. An astounding diversity of life is found in the coral reef ecosystem, which might overcome the coral by either stripping away all its mucus or eating the coral itself. Predators are treated to a virtually unlimited supply of tropical fish and crustaceans to feast upon without having to search away from the reefs into open ocean. The reefs also provide some predators protection from violent waves or currents. This balances the reef ecosystem by putting a limit on the number of fish eating away at the coral.
Some reefs form atolls surrounding small islands in warm ocean water, and limit the erosion that the waves usually cause to shorelines. Small islands can then develop safe navigable harbors where people can safely reside. Humans form the most tenuous link in the symbiosis of the ecosystem. Although they benefit from the safe harbors and plentiful fishing available near coral reefs, they can also destroy the reefs from their greed. Overfishing or tourism can quickly cause irreparable harm to coral reefs that have been around for tens of thousands of years.
Coral reef ecosystems are both diverse, enduring, and yet fragile at the same time. Humans need to be the guardians of these masterpieces of nature. If they succeed, they will finally complete the symbiotic environment of the reefs.