Why Are Starfish Keystone Species?

Starfish are considered keystone species because they play a crucial role in maintaining ecosystems by controlling populations of seaweeds and sea snails, sea urchins, limpets, and other communities they feed on. The absence or decline of starfish can lead to a significant imbalance within their habitats.

In the vast and diverse ecosystem of our oceans, certain species play crucial roles in maintaining balance and stability. These species, known as keystone species, exert a disproportionately large influence on their environment, shaping the structure and functioning of the entire ecosystem. 

One such remarkable keystone species is the starfish, also known as the sea star. Despite their seemingly simple appearance, starfish possess unique attributes and ecological interactions that make them indispensable to the health and resilience of marine ecosystems. 

This article explores the reasons why starfish hold the vital position of keystone species and the significant impacts they have on the complex web of life beneath the waves.

The Role of Starfish in Ecosystems

As keystone species, starfish play an essential role in maintaining balance and diversity within their ecosystems. They regulate the population of other organisms, thereby preventing any single species from becoming too dominant or overpopulated. A balanced ecosystem allows various species to coexist and flourish in harmony.

To better understand their impact, let’s explore some examples of the organisms starfish consume and protect:

  • Clams: By feeding on clams, starfish prevent excessive filtering of water and substrate disturbance caused by clams’ burrowing activities. This control contributes to maintaining the overall ecological balance of the ecosystem.
  • Snails: Excessive snail populations can have significant ecological impacts, such as overgrazing of algae and disrupting the balance of the benthic community. Starfish help keep snail numbers in check, promoting a healthier and more balanced ecosystem.
  • Mussels: Starfish help control mussel populations, which, if left unchecked, can quickly grow and monopolize space and resources, ultimately limiting the growth of competing organisms.
  • Barnacles: Similar to mussels, barnacles can quickly cover surfaces if their numbers are not kept in check. Starfish consume them and contribute to controlling their population growth.
  • Seaweeds: While most species of starfish typically dont consume seaweeds, they can protect various types of seaweeds by feeding on herbivorous sea creatures, such as sea urchins, that would otherwise consume the seaweed extensively.

By managing the populations of these organisms, starfish maintain the overall health and balance of their ecosystems, allowing many species to coexist and thrive.

How the Decline of Starfish Can Impact the Ecosystem

When starfish populations decline or are removed from ecosystems, the balance they maintain is disrupted, negatively affecting entire marine habitats. One particular event that highlights the importance of starfish is the sea star wasting disease (SSWD), a devastating disease that has led to a drastic decline in starfish populations across the Pacific Coast.

The following illustrates the repercussions of starfish removal or decline:

  • Imbalance in prey populations: With fewer starfish around, their prey species, such as mussels, barnacles, and sea urchins, can rapidly increase in number, occupying excessive space and resources. This, in turn, decreases the available habitat for other species.
  • Reduction in biodiversity: The decline in starfish can result in a decrease in overall biodiversity as their prey species outcompete other marine organisms for food and space, leading to an ecosystem imbalance.
  • Trophic cascade effects: The removal of a keystone species like starfish can trigger a chain reaction, or trophic cascade, across multiple levels of the food chain, directly or indirectly impacting various species within the ecosystem.

In light of these consequences, starfish conservation becomes increasingly important. By preserving their populations, we also safeguard the delicate balance in marine ecosystems they help maintain.


Keystone species like starfish play a vital role in maintaining the balance and stability of ecosystems by regulating the populations of various organisms. Their presence ensures that no single species becomes too dominant, allowing for a diverse and harmonious marine habitat. 

By preserving starfish populations, we can continue to protect the delicate web of life in marine ecosystems and ensure a thriving environment for numerous species to coexist for generations to come.