Biodiversity, or biological diversity, refers to the variety of living things in an area. Diversity is higher in complex environments than in simple ones. Complex physical environments have a lot to offer organisms in the way of food and housing. Estuaries, shorelines, and coral reefs are extremely complex marine environments, and each of them provides a wide assortment of nutritional resources for living things.
There are thousands of habitats in estuaries, coastal systems where fresh and salt water meet and mix. The bottom of the estuary provides homes for different kinds of organisms. Some spend their entire lives on the surface of the sediment, many burrow just under the surface, and others dig deep into the sediment. Organisms also select locations that accommodate their abilities to tolerate salt, so those that are adapted to high salinity are on the seaward side while the freshwater-dependent ones are on the river side. In between the two extremes, organisms live in zones that meet the salinity requirements for their bodies.
Diversity is an important aspect of a healthy ecosystem. In an ecosystem where all living things are exactly the same, one big change in the environment could cause widespread destruction. This might be best understood in a familiar ecosystem, like a forest. If only one kind of tree is growing in the forest, a virus that damages that type of plant could wipe out the entire forest. If the forest contains 20 different kinds of trees, it is unlikely that one disease agent could destroy the entire plant community. A high degree of biodiversity gives an ecosystem an edge, ensuring that it can continue to exist and function regardless of changes around it.
Despite their impressive biological and physical diversity, coral reefs must remain in balance to flourish. The equilibrium of nonliving factors such as sunlight, nutrients, and temperature with living factors such as population size and food supply constantly adjusts and fine-tunes itself. As in any ecosystem, each part of the reef community is dependent on its other parts. If one component of the reef is disturbed, the entire community has to adjust.
For the observer, an opportunity to view reef organisms in their environment is like attending a living museum in natural history. Some reefs are homes to types of organisms that have been in existence for thousands of years. These life forms boast genealogies longer than any organisms in landbased ecosystems. Some of the present-day coral reefs were thriving when the land adjoining them was first populated with humans. Reefs have played an important cultural role in developing nations and are part of the history of the sea and lands they border.