From starfish to sharks: the fascinating world of marine reproduction (Part I)

Since the dawn of life on Planet Earth (or the Blue Planet), species of both flora and fauna have continuously adapted to the ever-changing conditions of their surroundings to ensure their survival. Among the many factors that influence a species’ continuity, reproduction stands out as one of the most crucial. It is the biological process by which new organisms are created.

Throughout evolution, a wide array of fascinating reproductive methods has emerged, highlighting the significance of this process. The marine environment is no exception: marine species have developed a variety of complex reproductive strategies, each uniquely suited to ensure their long-term survival.

Broadly speaking, there are two main types of reproduction in the marine environment. On one hand, there is asexual reproduction, where a single individual can create new individuals without the involvement of sexual cells or gametes. On the other hand, there is sexual reproduction, where individuals of opposite sexes come together to form new individuals, this time with the involvement of sexual cells or gametes.

In this first text on reproduction in the marine environment, we are going to deal with one of the most primitive forms: asexual reproduction in marine fauna. In this type of reproduction, the offspring come from a single adult individual or progenitor, as mentioned above. There are several modes within this type of reproduction. In some species of cnidarians, new individuals are formed from outgrowths or buds in a process known as budding. These new individuals can detach from the parent or remain attached, forming numerous and dense colonies, as seen in certain species of sponges and corals, among others.

Sea sponge during the process of budding, in which the progenitor, by means of gravity, stretches until it divides into two identical individuals.

To cope with natural disturbances like predation or storms, new organisms can also develop from fragments that break off from the adult. This phenomenon is known as fragmentation or fission, and starfish are a notable example of this type of reproduction. In addition to starfish, some species of polychaetes and corals can also reproduce in this manner. Specifically, when a starfish loses an arm and conditions are favorable, it can regenerate and grow back. Moreover, a completely new individual can develop from this detached arm.

Echinaster sepositus

Although there are other modes of asexual reproduction, the last one we want to discuss is parthenogenesis. This is a peculiar phenomenon used by certain species, such as some sharks, to reproduce asexually when females cannot find individuals of the opposite sex for sexual reproduction.

This particular case clearly illustrates how evolution has led to the development of reproductive strategies to ensure the survival of species throughout Earth’s history. However, as we mentioned at the beginning, species can reproduce not only asexually but also sexually. If you are interested in this topic and want to learn more about marine reproduction, especially sexual reproduction, stay tuned to our social media!