Which algae covers thousands of hectares in Sargasso sea.

Explanation

### Step-by-Step Solution:

1. **Identify the Location**: The question asks about algae that covers a large area in the Sargasso Sea. The Sargasso Sea is a region in the Atlantic Ocean known for its distinctive characteristics.

2. **Recognize the Type of Algae**: The algae in question is a type of seaweed. It is important to note that there are various types of algae, including green, red, and brown algae.

3. **Determine the Specific Algae**: The specific algae that is known to cover thousands of hectares in the Sargasso Sea is called **Sargassum**.

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