In the oceans there are a variety of animals with special capacities to survive in a very challenging environment. Among these are corals. The reproductive system of corals is amazing. Corals are fixed to the ocean floor or to objects beneath the ocean and therefore are not able to move around to find mates. Corals use various asexual reproduction methods. However, the sexual reproduction of hermaphroditic corals is nothing short of amazing!
In the polyps of the coral colony there are small bundles resembling seeds, some containing eggs and some containing sperm. At a certain time, once a year, these are released into the water. These bundles drift slowly to the surface where they pop open and mix with others on the surface to form a spawn “soup.” Eggs and sperm in this soup are united and then drift with the currents to reach new locations where they establish new coral colonies.
The amazing thing is the timing of the release. It occurs on the eighth day following the full moon in August. This phenomenon was only discovered in 1982 in Australia’s Great Barrier Reef. Since then researchers have found that most large reef-building corals use this method of simultaneous release of eggs and sperm at the precise moment. This mass spawning is so amazing that it has fascinated scientists and excited the few who have been able to observe it.
No one fully understands what triggers the spawning event or how the corals synchronize to spawn at the same time. However, the timing is correlated with lunar cycles. The gravitational pull of the moon creates the ocean tides. The mass spawning release occurs at neap time, which is the time when the difference between high and low tides is the smallest. This gives the eggs and sperm maximum time for uniting before being washed away by the tide. Perhaps at this time there are fewer predators hunting. Since the release occurs at night, it may be difficult for predators to see the released sperm and eggs. Even if they do see it, there is such an enormous amount of material released that it overwhelms the fish predators who cannot possibly consume all of it. After the fertilization, the high tides return and carry the fertilized eggs along the coast to new areas where the coral larvae attach themselves and start new colonies.
Although the spawning period may last for only a few hours one day each year, it is essential for the coral reefs around the world. The coral reefs play a very important role in ocean life, which in turn is essential to all forms of life. This spawning event is one which few human beings have been privileged to witness, but one who did described it as “an upside-down snowstorm of iridescent orange, white and red.”
How do the corals know the right time to release their spawn to give maximum probability for survival? Who programmed them to perform this amazing event? We believe this is another example of a Dandy Design by the Creator.
National Geographic, January 1991, page 58
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