One of the most common methods of reproduction in the sea is broadcast spawning. Sometimes called mass spawning or synchronous spawning, broadcast spawning takes place when animals release their eggs and sperm into the water, where fertilization occurs externally.

Broadcast spawning is common in many mollusks and other invertebrates. Species like limpets, clams, sea anemones, fan worms, and jellyfish all reproduce externally by releasing their sperm and eggs to be fertilized by their neighbors. Some species like the Moon Jellyfish release only sperm by males, which is then collected by females to fertilize their eggs internally.

When broadcast spawning occurs the surrounding waters become cloudy with the tiny gametes. Broadcast spawning is often critically timed when conditions are ideal to increase the success rate of reproduction.

In the Gulf of Mexico, many coral species spawn a few days after the full moon in August during a time frame of 30 minutes to an hour.[1] During this time, thousands of gamete bundles containing either sperm or eggs are released. These bundles float to the surface of the water where they fertilize each other, creating larvae. These larvae then become part of the zooplankton as they float on the surface for a few days. Then they drift back down to new locations to form new colonies and eventually new reefs. According to Dr. David Vaughan, Director of the Center for Coral Reef Research at the Mote Marine Laboratory in the Florida Keys, “it’s kind of like upside-down snow.” The Deepwater Horizon oil spill is of great concern to coral biologists. If the oil spill enters an area where coral spawning is occuring, it could cause severe damage to the coral larvae that only are only produced once every year.

Broadcast Spawning Coral

Coral Spawning

Resources for Broadcast Spawning

[1] Deepwater broadcast spawning by Montastraea cavernosa, Montastraea franksi, and Diploria strigosa at the Flower Garden Banks, Gulf of Mexico