Everyone comes to the Great Barrier Reef to experience the beautiful coral gardens, that are the foundation of the world’s largest living structure. With ABC Snorkel Charters Port Douglas, you can be one of the fortunate people to see the best of the best. This natural icon is so large, it is larger than the Great Wall of China and is visible from space! Coral reefs are among the most diverse ecosystems in the world. They’re home to a quarter of all marine species, yet they only comprise 1% of the ocean bottom. Originally, they were formed over 25 million years ago, but the reefs we see today were probably formed eight-to-ten thousand years ago.
Many think that coral is a plant or a rock, but in fact, they are many animals which are related to Anemones and Jellyfish. Each coral comprises a colony of animals called polyps, which live and thrive as a community. Every polyp has a sac-like body and a small opening at one end, their mouth, surrounded by tentacles. These tentacles are used for defense, to clear away debris and to feed. Most corals feed at night. To feed, the polyp extends these stinging tentacles to capture prey floating along. It is then fed into the mouth, digested in their stomach, and any waste is expelled through the same opening. The polyp uses calcium and bicarbonate ions from seawater to build itself a hard, cup-shaped skeleton made of calcium carbonate or limestone which protects the soft, delicate body of the polyp. The polyp secretes a layer of calcium carbonate underneath its body, thus creating the foundation from which reefs form and grow.
On a voyage out of Port Douglas with ABC Snorkel Charters, you will see many and varied Reef-building corals, or hard corals which are joined inside a limestone skeleton by an algae called zooxanthellae that lives within their tissues. They have a symbiotic relationship, whereby the coral provides the algae with carbon dioxide and a home, and the algae provides the polyp with nourishment and their amazing, vivid colours.
Corals come in a wide range of shapes. Digitate corals look like fingers or clumps of cigars. Table corals are table-like structures. Encrusting corals form a thin layer against the substrate. There are massive boulder or ball-shaped corals, branching corals that resemble a maze of tree limbs, and other corals that look like food items, such as lettuce or cauliflower or mushrooms. One of the most impressive events you can witness in the ocean is a mass coral spawning event.
Corals are hermaphrodites, possessing both male and female reproductive cells. During a spawning event, a massive number of eggs and sperm is released into the water column over a broad geographic area. This is a synchronised event, whereby all coral species in an area release their eggs and sperm at the same time, as corals cannot move into reproductive contact with each other. This usually occurs in response to multiple environmental cues, including a full moon, day length, tide height and water temperature. Within the Great Barrier Reef this spectacular event occurs on inshore reefs up to six nights after the first full moon in October, and during November or December on outer reefs. Species will spawn on different nights to ensure cross-breeding of coral doesn’t occur. Spawning resembles an underwater snowstorm.
Coral reefs are not only important to the marine species that they shelter for breeding, feeding or cleaning, they also offer a buffer to adjacent shorelines from wave action preventing erosion. Over half a billion people globally are estimated to live within 100 kilometres of a coral reef, due to the food they provide and the opportunities for livelihoods, including local economies through tourism. Snorkel and diving tours, fishing trips, hotels, restaurants and other services located near coral reefs provide millions of jobs and contribute billions of dollars worldwide.
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