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
- Biodiversity and conservation
- Climate change impacts
- Food production systems (fisheries and aquaculture)
Types of Aquatic Ecosystems
1. Freshwater Ecosystems
- Rivers, lakes, wetlands.
- Key for human water supply and agriculture.
- Vulnerable to pollution, damming, and invasive species.
2. Marine Ecosystems
- Oceans, coral reefs, mangroves.
- Provide food, regulate climate, and support immense biodiversity.
- Threatened by overfishing, plastic pollution, and ocean acidification.
3. Wetlands
- Transitional zones between land and water.
- Act as natural filters, flood protection, and biodiversity hotspots.
- Often drained for agriculture and urban development.
Threats to Aquatic Ecosystems
The syllabus emphasizes human pressures and natural challenges:
- Eutrophication: nutrient pollution leading to algal blooms and dead zones.
- Overfishing: collapse of fish populations (e.g., North Atlantic cod).
- Pollution: plastics, oil spills, heavy metals.
- Climate change: rising sea levels, coral bleaching, melting Arctic ecosystems.
- Habitat destruction: dredging, dam construction, and wetland drainage.
Conservation Strategies
In-Situ Approaches
- Marine protected areas.
- Wetland restoration projects.
- Legislation to regulate fishing and pollution.
Ex-Situ Approaches
- Breeding programs for endangered aquatic species.
- Genetic banks for corals and fish.
ESS requires you to evaluate effectiveness:
- Are marine protected areas effective if not enforced?
- Is aquaculture sustainable, or does it create new pollution problems?
Case Studies You Can Use
- The Great Barrier Reef (Australia): coral bleaching and climate change impacts.
- The Aral Sea (Central Asia): collapse of aquatic ecosystems due to irrigation mismanagement.
- Lake Victoria (Africa): invasive Nile perch disrupting native biodiversity.
- North Atlantic Cod Fisheries: overfishing leading to population collapse.
Aquatic Ecosystems in ESS Exams
Paper 1
Expect case study booklets featuring water-based ecosystems, often with graphs, data, or maps of pollution levels or biodiversity loss.
Paper 2
Typical essay questions include:
- “Discuss the impacts of human activity on aquatic ecosystems.”
- “Evaluate conservation strategies for aquatic ecosystems.”
Exam Tips
- Think systems: show how pollution in one part of the water cycle impacts entire ecosystems.
- Balance evaluation: conservation strategies have both strengths and weaknesses.
- Use case studies smartly: mention specific names and outcomes, not just general terms.
FAQs
1. Do I need to know specific aquatic species?
Yes, especially indicator species. For example, corals in reef ecosystems or invertebrates in rivers can be used as exam evidence.
2. How much detail is required about marine ecosystems?
Not deep marine biology, but you should know key processes and threats, such as ocean acidification and overfishing.
3. Could aquatic ecosystems appear in a data analysis question?
Absolutely. Expect graphs on dissolved oxygen, biodiversity, or fish stock trends. You’ll need to interpret them and link back to ecological processes.
Conclusion
Aquatic ecosystems are woven throughout the ESS syllabus because they highlight the delicate balance between human needs and environmental sustainability. Whether it’s freshwater scarcity, marine biodiversity, or wetland protection, you’ll need to show an ability to analyze, evaluate, and apply case studies. By mastering this topic, you’ll be ready for one of the most frequently tested areas of the 2026 ESS exams.
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