What happens to the ocean if we take out all the fish? A marine ecologist explains the complex roles fish play in their ecosystem

• What would happen to the ocean if we took out all the fish?
• – Reny, age 12
  What would happen to the ocean if we took out all the fish?
• – Reny, age 12 The ocean is massive and covers most of the surface of our planet.
• These fish perform all kinds of roles in their ecosystems that support the lives of other organisms around them.

I’m a scientist who studies fish, their diversity and all the ways they contribute to ocean environments.

Fish as food

Fish play important roles as both predators and prey in ocean ecosystems. Thousands of species throughout the ocean and terrestrial ecosystems rely on fish for food – including people. In coral reef ecosystems, small fish are eaten by larger fish and other marine animals. This means the little fish form the base of the food web – they provide energy to the bigger fish and other creatures.

• Outside of the water, many birds, mammals and reptiles eat fish and rely on them as an essential source of protein.
• Even land plants can benefit from the presence of fish.
• Humans also depend on fish as a food source.

Fish maintain habitats

• As fish themselves forage for food, they can create and maintain important habitats for other organisms.
• Without the help of these herbivores, or plant-eating fish, the algae would rapidly grow and smother the coral, effectively killing it.
• Other fish create habitats for other animals and influence their environment by disturbing sand while they feed.
• Despite the fact that many types of fish are confined to the ocean, their presence can be felt across many habitats.

Kory Evans receives funding from National Science Foundation.