How Do Starfish Reproduce Sexually and Asexually?

Starfish (Asteroidea) are marine invertebrates found from the intertidal zone down to the abyssal depths of 6,000m and below. They normally have a central disc and five arms, giving them their infamous star shape. Nevertheless, there are 2,000 known species of starfish, and so, they vary from habitats to size and colours.

The average lifespan of a starfish is 35 years. These sea stars are carnivores and feed on coral, sponges, clams, oysters, sand dollars, and mussels. They do this by first extending their stomach out of their mouth and over the digestible parts of its prey. The prey's tissue is partially digested externally before the soup-like "chowder" produced is drawn back into the starfish's 10 digestive glands. Learn more in our article about what starfish eat.

And so, you see, although these sea creatures are beautiful and seem to merely be resting on a rock or the sand, there's actually a lot more to their existence and survival. One of their many mysteries was how they reproduce. Continue reading to learn more about starfish!

Starfish are incredible creatures with a fascinating lifestyle. One of the most fascinating things about them is how they reproduce. This is because starfish can reproduce sexually, by mating with another starfish, or asexually, by making a copy of themselves but at a high price.

Let's first take a look at their main type of reproduction: sexual reproduction. Then, we'll see the difference to their asexual reproduction.

The reproduction of starfish begins when the right environmental conditions exist. Most of them reproduce during the warmer season. Many also choose the days of high tide. Then, to sexually mate they spawn. This means that they mate by releasing their sex cells into the water.

Starfish do this by gathering in groups called “spawning aggregations”. This increases the likelihood that the sperm and egg will find each other. Starfish have sexual organs, also called gonads, on each of their arms. It's important to mention that mating strategies can slightly vary from species to species.

Once in their spawning aggregation, starfish interlock their arms. This causes the synchronized release of gametes by both sexes, females release their eggs and males their sperm. This is how external fertilization occurs, the beginning of the life cycle of a starfish. This type of mating is called pseudocopulation, since there is physical contact but no penetration.

There is no pregnancy, embryos are formed and developed in the water. In some species they will form and develop on the body of the parents. Therefore, most starfish are oviparous, as the embryos is formed and developed externally. However, there are certain species of starfish, like the Patiriella vivipara, that are viviparous as their young develop within the gonads of their parents. They become fully independent and leave their parents once they have fully developed their 5 arms.

In some species, such as the sand star (Archaster typicus), pseudocopulation is done in pairs. A male stands on top of a female, interspersing his arms. Viewed from above, they look like a single ten-pointed star. They can stay like this for a whole day, so much so that, many times, they are covered by sand. Lastly, as in the previous case, both release their gametes and external fertilization occurs.

In the latter case, although the mating is done in pairs, they are also added in groups. That way, they increase their chances of reproducing, as well as having several offsprings throughout the same reproductive season. Therefore, starfish are clearly polygamous animals.

You may also be interested in our article about the endangered animals of the great barrier reef.

Starfish can also reproduce without mating. So, how can starfish reproduce asexually? Well, starfish have the ability to regenerate lost arms. When an arm is damaged in an accident, it can be dislodged. They also do it, for example, when they are chased by a predator with the aim of entertaining them while they escape. Later, they begin to re-form the lost arm. However, this is a very expensive process that can take several months.

Some species can regenerate their entire body from a detached arm. Although they can only do this if they keep at least 1/5 of their central disk. As we've previously mentioned, starfish's body is divided into five equal parts. Therefore, not only do they have five arms, but their central disc is also pentameric. When the necessary conditions are met, this central disk breaks or splits into two or more parts (up to five), each with its corresponding arm.

Therefore, if a starfish detaches 1/5 of their arm and central disk, they will reproduce themselves. This means that the new individual will be identical to their progenitor. This type of asexual reproduction has been found in many individuals of the Aquilonastra corallicola starfish species.

You may also be interested in our article about on animals without a brain.

Image: ElPaís

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