---
title: "Predator Loss and Ecosystem Effects"
description: "Quantify energy transfer efficiency through trophic levels (~10% rule); explain trophic cascades: how removing an apex predator triggers a chain of ecosystem changes (sea otters → sea urchin explosion"
canonical: https://lightmysky.com/learn/science/predator-loss-and-ecosystem-effects-mt_NPTjGJIyb3
source: https://lightmysky.com/learn/science/predator-loss-and-ecosystem-effects-mt_NPTjGJIyb3.md
retrieved: 2026-10-19
---

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# Predator Loss and Ecosystem Effects

Quantify energy transfer efficiency through trophic levels (~10% rule); explain trophic cascades: how removing an apex predator triggers a chain of ecosystem changes (sea otters → sea urchin explosion → kelp forest collapse); define 'fishing down the food web'; evaluate evidence for ocean rewilding: shark reintroduction, whale recovery driving nutrient cycling; understand why ecosystem-based fisheries management is needed

Subject: Science · Area: Ocean Life · Ages 12 to 14
Page: https://lightmysky.com/learn/science/predator-loss-and-ecosystem-effects-mt_NPTjGJIyb3

## Lesson: When One Predator Disappears: Trophic Cascades

Every food chain moves energy from one living thing to the next. Scientists call each step a trophic level: algae and plants first, then plant-eaters, then meat-eaters, then top predators. At each step, an animal uses most of its energy just to breathe, move, and grow. Only about 10 percent of that energy gets passed up to whatever eats it next. That single rule explains why the ocean holds huge amounts of plankton but only a few sharks. Big predator fish recover slowly when boats catch too many.

*(drawing: Energy shrinks by about ten times at each level up the food chain. That is why top predators are always rare.)*

**Example.** Sea otters eat sea urchins. Sea urchins eat kelp. In the 1800s and 1900s, hunters killed most sea otters along the Pacific coast for their fur. With almost no otters left to eat them, sea urchins multiplied out of control. The urchins chewed through entire kelp forests, leaving bare rocky patches called urchin barrens, where almost nothing else could live.

*(drawing: One missing predator set off every step in this chain.)*

This ripple effect is called a trophic cascade. People caused a similar problem by fishing down the food web: after boats caught most of the big predator fish, they moved on to smaller and smaller fish, and whole food webs got thinner from the top down. Now some places are testing ocean rewilding, bringing back sharks and letting whale numbers recover, since whales carry nutrients up from deep water and feed tiny ocean plants near the surface. That is why fisheries rules today try to manage whole ecosystems instead of counting just one fish species.

**Recap.** Removing a single predator can collapse an entire ecosystem, which is why modern fisheries protect whole food webs instead of one species at a time.

## Practice

8 questions on this page, each with its working shown.

## Needs first

- [Ocean Pollution & Harm](https://lightmysky.com/learn/science/ocean-pollution-and-harm-mt_J6uccv2Bo4)
- [Ocean animal migrations](https://lightmysky.com/learn/science/ocean-animal-migrations-mt_Te-ulgYMUd)

## Opens up

- [Coral Bleaching & Acidification](https://lightmysky.com/learn/science/coral-bleaching-and-acidification-mt_EXO1bJ3G_v)