There are 2,000 species of starfish, also known as sea stars or Asteroidea, living in the world’s oceans. Though these invertebrates have no brains or blood, they’re more than capable of reproducing; females can even spawn up to 65 million eggs at once. With an average lifespan of 35 years in the wild, that’s a whole lot of starfish in the ocean.
Both male and female sea stars hold their sperm and eggs in pouches at the base of their arms. They reproduce by free spawning, that means ideally the male and female release their eggs and sperm at the same time. The egg and sperm float until they meet up and the sperm is able to fertilize the egg. This is most likely to happen if a large number of starfish have gathered in the same area and spawn at the same time. As you may imagine, the strength and direction of ocean currents also plays a role in how many babies a pair of sea stars can produce.
Starfish babies are extremely tiny and nearly invisible to the naked eye; they measure a whopping 1 millimeter. This allows ocean currents to sweep these babies alongside plankton and algae for miles and miles. During this time, these tiny sea star larvae feed on miniscule plants and animals floating nearby in the ocean. They also run the risk of becoming food for plankton- and algae-loving animals like whales.
After a month or two infant starfish begin looking less like tiny blobs of jelly and more like small sea stars. At this point the baby sea stars metamorphosize into star-shaped creatures. They start growing a variety of tubes, which will eventually become their arms, in order to catch and feed on algae. For the next six months the juvenile sea star grows very slowly. These teenage starfish prefer to make their homes hiding under reef rocks and rubble, far from predators, until they are large enough to travel in search of food. Most marine animals don’t find calcified adult sea stars very tasty, however infant or juvenile starfish sometimes fall prey to whales or fish and even other sea stars.
A sea star is considered an adult and ready to reproduce around 2 years old. During this time adult sea stars traverse the ocean floor and coral reefs preying on shellfish, sea urchins, sea cucumbers and other sea stars. If starfish seem like carefree beauties filling their bellies and producing babies galore, that’s because they sort of are; with few natural predators, sea stars even have the ability to regrow limbs. On top of that, some species can regrow a completely new body from a single, severed arm.
Christina Stephens is a writer from Portland, Ore. whose main areas of focus are pets and animals, travel and literature. A veterinary assistant, she taught English in South Korea and holds a BA in English with cum laude honors from Portland State University.