Plot

Coral reefs are the rainforests of the sea; fish compete for food, territory and mates within this oasis of life. Incredible time-lapse photography shows the dramatic formation of a coral reef, portraying its inhabitants and its ultimate destruction.—Anonymous

Coral reefs are so crowded that they play host to a perpetual battle for space, even among the coral itself. Every individual has to find their own place and their own way of surviving.

Corals start life as a larva that becomes a Polyp. Having multiplied, it hardens into a limestone skeleton and grows to form a reef. The corals provide the foundations on which the entire reef community survives. As the community flourishes, animals develop relationships with one another and such a place can feature a huge variety of ocean life.

Reefs are home to an astounding number of fish, including the smallest and the largest fish in the sea. Whale sharks are largest fish, who only visit the reefs when nutrient rich waters arise from the deep. Reefs are made of layer upon layer by millions and millions of individual animals. A single reef can extend for many miles.

Reefs are only found in the shallow and warm waters of the tropics. Although corals feed nocturnally on plankton, sunlight is vital because even though they are animals, each contains millions of single-celled algae. Algae convert the sunlight into sugars using photosynthesis. 98% of the food that the corals consume is produced by the algae.

This in turn is the favored sustenance of the hump head parrot-fish, whose jaws are so powerful that it erodes much of the reef into fine sand. The parrot-fish plays a large part in the erosion of the reef. Over time, the sand is drifted by waves and into an island, which is inhabited by animals. Algae also grows on the top of the reef and a battle for grazing rights between shoals of powder blue and convict tangs are shown, the former being initially overwhelmed by the latter's weight of numbers before regaining the upper hand. There are several instances of 2 predators fighting each other to retain grazing rights over their part of the reef. Although some predators tend to avoid conflict as well.

Some species of shrimp also make their home inside the corals. These shrimps have a social structure similar to that of bees as they have a queen, who is the only one to lay eggs, and each member of the colony has a specialized task such as guards (who have especially sharp and long claws). A worm enters the coral and is repelled by the fighting guards.

At night, the corals take in water, extend their tentacles and emerge to feed. Inevitably, the corals being to outgrow each other. Corals extrude their guts and simply digest their neighbors alive. Corals are attacked by predators such as the crown of thorns starfish. Some corals have crabs living inside their colony who help the corals defend their home against predators. The top of the reefs is covered with a layer of green algae, and many fish depend on it.

The night-time hunting of a marbled ray alerts other predators and a group of white-tip reef sharks moves in, from which few are safe. At night, vision is of little use, but the sharks can use the sense of smell and a form of electrical reception to identify their prey. There is no place to hide for the smaller fish during these feeding frenzies.

Life on the reef is not only about food, but also about breeding. Fish want to maximize the number of offspring that will survive. Several breeding strategies are examined, including the acrobatic habits of brown surgeon-fish (the female jump and release the eggs in the water, while the male compete for the right to fertilize them) and the colorful courtship of the flamboyant cuttlefish. The pipe-fish engage in an elaborate dancing ritual to affirm their bond with each other before the female releases her eggs into the male. The male carries the eggs to gestation, which takes about 20 days. In the meantime, the female produces another batch of eggs in 10 days, which she deposits in another male, thereby doubling the number of offspring they can produce in a year.

Predators lurk in the water to feast on the nutritious eggs.

Humpback whales are visitors to the reef and males establish their seniority by the loudness and strength of their song. Being fixed to the seabed, corals must synchronize their reproduction with lunar phases and the rising spring temperatures. Some corals are male and release sperm which are carried by the water currents to the female corals.

Some species of corals are both male and female. They release packages of eggs which are already wrapped in sperm. The stormy seasons brings real danger to the animals in the reef. Some lobsters risk crossing through an exposed area next to the corals to seek shelter in deep ocean waters. They make this journey every year. They reach the edge of the reef and go down. Hurricanes can threaten the very structure of the reef itself.