The correct answer is option 3: Producers. Algae are photosynthetic organisms that convert sunlight energy into organic compounds through the process of photosynthesis. They use this energy to produce their own food, making them primary producers in the ecosystem.

Option 1: Decomposers refers to organisms that break down dead organic matter, such as bacteria and fungi. Algae do not primarily play this role in the ecosystem.

Option 2: Destructors is not a commonly used term in ecology. It does not accurately describe the role of algae in the ecosystem.

Option 4: Consumers refers to organisms that consume other organisms for food. While some organisms may consume algae, algae themselves are not classified as consumers, but rather as producers.

Therefore, the correct classification for algae in the ecosystem is as producers.