Final answer:
Reduction in phytoplankton leads to reduced fish populations in the Indian Ocean due to an ecological chain reaction caused by the decline in primary producers.
Explanation:
Reduction in phytoplankton can lead to a reduction in fish populations in the Indian Ocean due to the ecological chain reaction it triggers. Phytoplankton, as primary producers, serve as the base of the food web. When their numbers decline due to factors like El Niño, fish that rely on them for food also suffer, leading to a decrease in fish populations.
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