Most stony corals are broadcast spawners and fertilization occurs outside the body (external fertilization).
Depending on the species and type of fertilization, the larvae settle on a suitable substrate and become polyps after a few days or weeks, although some can settle within a few hours!
There are two types of sexual reproduction in corals, external and internal. In sexual reproduction, eggs are fertilized by sperm, usually from another colony, and develop into a free-swimming larva. This is called fragmentation, which can occur as a result of a disturbance such as a storm or being hit by fishing equipment. Sometimes a part of a colony breaks off and forms a new colony. Corals do this throughout their lifetime. Budding is when a coral polyp reaches a certain size and divides, producing a genetically identical new polyp. Asexual reproduction is important for increasing the size of the colony, and sexual reproduction increases genetic diversity and starts new colonies that can be far from the parents.Īsexual reproduction results in polyps or colonies that are clones of each other - this can occur through either budding or fragmentation. ReproductionĬorals have multiple reproductive strategies – they can be male or female or both, and can reproduce either asexually or sexually. All corals are in the phylum Cnidaria, the same as jellyfish. The hexacorals (including the true stony corals and black corals, as well as the sea anemones) have smooth tentacles, often in multiples of six, and the octocorals (soft corals, seafans, organpipe corals and blue corals) have eight tentacles, each of which has tiny branches running along the sides. All but the fire corals (named for their strong sting) are anthozoans, which are divided into two main groups. The family tree of the animals we call corals is complicated, and some groups are more closely related to each other than are others. There are also corals that use more flexible materials or tiny stiff rods to build their skeletons-the seafans and sea rods, the rubbery soft corals, and the black corals. Stony corals are the most important reef builders, but organpipe corals, precious red corals, and blue corals also have stony skeletons.
In the so-called true stony corals, which compose most tropical reefs, each polyp sits in a cup made of calcium carbonate. The less common purple, blue, and mauve colors found in some corals the coral makes itself. It is this relationship that allows shallow water corals to grow fast enough to build the enormous structures we call reefs. The zooxanthellae also provide much of the green, brown, and reddish colors that corals have. These single-celled algae photosynthesize and pass some of the food they make from the sun’s energy to their hosts, and in exchange the coral animal gives nutrients to the algae. Shallow water corals that live in warm water often have another source of food, the zooxanthellae (pronounced zo-o-zan-THELL-ee). Corals differ from sea anemones in their production of a mineral skeleton. Inside the body of the polyp are digestive and reproductive tissues. The tentacles have stinging cells, called nematocysts, that allow the coral polyp to capture small organisms that swim too close. The polyp is like a tin can open at just one end: the open end has a mouth surrounded by a ring of tentacles. What Are Corals? Animal, Vegetable & MineralĬorals are related to sea anemones, and they all share the same simple structure, the polyp. In some places, reefs have been entirely destroyed, and in many places reefs today are a pale shadow of what they once were.
Overfishing and destructive fishing, pollution, warming, changing ocean chemistry, and invasive species are all taking a huge toll. Unfortunately, people also pose the greatest threat to coral reefs. dollars each year, providing food, protection of shorelines, jobs based on tourism, and even medicines. dollars and perhaps as much as 172 billion U.S. The value of coral reefs has been estimated at 30 billion U.S. Because they are so diverse, coral reefs are often called the rainforests of the sea.Ĭoral reefs are also very important to people. This is a remarkable statistic when you consider that reefs cover just a tiny fraction (less than one percent) of the earth’s surface and less than two percent of the ocean bottom. They teem with life, with perhaps one-quarter of all ocean species depending on reefs for food and shelter. Coral reefs are the most diverse of all marine ecosystems.
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