Introduction
Aquatic ecosystems are some of the most dynamic and diverse environments on Earth. They range from freshwater rivers and lakes to vast marine systems like oceans and coral reefs. In IB Environmental Systems and Societies (ESS), aquatic ecosystems are central to the 2026 first assessment syllabus, appearing in multiple sections such as resource use, biodiversity, pollution, and climate change.
Students often underestimate this topic, but it provides an excellent opportunity to integrate systems thinking and demonstrate exam-ready knowledge with case studies. Understanding how aquatic ecosystems function—and how humans impact them—is essential for achieving a top grade.
Quick Start Checklist for ESS Students
When revising aquatic ecosystems, make sure you can:
- Define types of aquatic ecosystems (freshwater, marine, wetlands).
- Understand flows of energy and matter within these systems.
- Explain the importance of aquatic ecosystems for biodiversity.
- Identify threats such as overfishing, eutrophication, and climate change.
- Evaluate conservation strategies (in-situ and ex-situ).
- Use case studies to illustrate your points.
Aquatic Ecosystems in the ESS Syllabus
The ESS course emphasizes the systems approach—inputs, outputs, storages, and flows. Aquatic ecosystems are excellent examples of this, showing how energy moves through trophic levels and how nutrients cycle in water-based environments.
You’ll encounter aquatic ecosystems in topics such as:
- Freshwater resources and pollution
- Global water crisis
