Which of the following correctly describes a major difference between freshwater and marine ecosystems?

• A. Both freshwater and marine ecosystems have the same types of fish species.
• B. Marine ecosystems are only found in lakes and rivers.
• C. Freshwater ecosystems have low salt concentrations, while marine ecosystems have high salt concentrations.
• D. Freshwater ecosystems cover a larger area of the Earth's surface than marine ecosystems.

Answer: (C)

Verified step by step guidance

1. Step 1: Begin by understanding the key difference between freshwater and marine ecosystems. Freshwater ecosystems, such as lakes, rivers, and streams, have low salt concentrations, typically less than 0.05%. Marine ecosystems, such as oceans and seas, have high salt concentrations, averaging around 3.5%. This is a fundamental distinction.
2. Step 2: Evaluate the first option: 'Both freshwater and marine ecosystems have the same types of fish species.' This is incorrect because freshwater and marine ecosystems support different species adapted to their respective environments. For example, salmon can live in both, but most species are specialized for one type of ecosystem.
3. Step 3: Evaluate the second option: 'Marine ecosystems are only found in lakes and rivers.' This is incorrect because marine ecosystems are found in oceans and seas, not in lakes and rivers, which are freshwater ecosystems.
4. Step 4: Evaluate the third option: 'Freshwater ecosystems have low salt concentrations, while marine ecosystems have high salt concentrations.' This is correct because it accurately describes the primary difference between these two types of ecosystems.
5. Step 5: Evaluate the fourth option: 'Freshwater ecosystems cover a larger area of the Earth's surface than marine ecosystems.' This is incorrect because marine ecosystems cover approximately 70% of the Earth's surface, while freshwater ecosystems cover a much smaller area.