Acanthaster planci are diecious (like the Eastern Swallowtail Butterfly and humans for example) meaning it has separate female and male sexes. Once fertilization begins the species undergoes deuterostome reproduction involving morphological changes from larvae to adult forms. The development of Acanthaster planci occurs in five stages after fertilization:

Fertilization: The breeding period for Acanthaster planci usually takes place between December and April, during which sexual reproduction occurs when eggs or sperm (gametes) are released into the water. They make their way into the pores on the central disk of the starfish where the eggs or sperm may land and become fertilized. Acanthaster planci has one of the highest rates of fertilization which is why "blooms" may occur so rapidly.

The ciliated gastrula stage (right) after fertilization, cell division, and growth. The gastrula are free-living and continue to develop into Bipinnaria larva.

Larva stage 1: During this stage the larvae swim along the ocean for about four weeks. With small hair-like structures called cilia they are able to move along the currents and reach plankton that they eat.

The earliest stage of larva form called the Bipinnaria larva (left). The "middle" stage of larva development, Brachiolaria larva (middle). The late stage of Brachiolaria larva beginning to settle and undergo metamorphosis (right).

Metamorphosis stage 2: The larvae will eventually settle on shallow reefs where they will undergo metamorphosis and become juvenile starfish. This process can take up to 2 days.

Image of a juvenile starfish just after metamorphosis.

Juvenile starfish stage 3: During this stage of about 6 months the starfish feeds on coralline algae and begins to grow.

A young juvenile feeding on coralline algae.

Juvenile starfish stage 4: This process has a duration ranging from 6 months to 2 years. The juveniles will begin to feed on corals and continue to grow until they become an adult.

A juvenile starfish feeding on coral (left) and a juvenile starfish growing into an adult (right).

Adult stage 5: After two years Acanthaster planci has become fully mature and has grown elongated spines for protection. A full grown adult can grow up to a meter or more in size.

Adult Crown-of-Thorns starfish.
Image taken from Wikipedia. Author: Jon Hanson. Original source from Flickr.

Now for a look at some of the Interactions between Acanthaster planci and other organisms!