Which organisms are the chief producers in oceans ?

Explanation

**Step-by-Step Solution:**

1. **Identify the Question**: The question asks which organisms are the chief producers in oceans.

2. **Understanding Producers**: In an ecosystem, producers are organisms that can produce their own food through photosynthesis or chemosynthesis. In the ocean, these are primarily photosynthetic organisms.

3. **Recognizing Key Organisms**: The main group of organisms that serve as primary producers in oceanic environments is known as phytoplankton.

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