Passage Summary: Warm water prevents nutrients from reaching tiny sea plants, which starves the tiny animals that eat them, eventually leaving fish and birds with nothing to eat.

Conclusion: Global warming will inevitably cause fish and seabird populations to decline.

Reasoning: Rising temperatures stop the mixing of seawater, which starves phytoplankton; since zooplankton eat phytoplankton and support the rest of the chain, the entire system collapses.

Analysis: The statement in question serves as a vital link in a causal chain that connects a physical change (temperature rise) to a biological outcome (population decline). By identifying the diet of zooplankton, the author explains *how* the lack of nutrients for phytoplankton eventually reaches the top of the food chain. In 'Role in Argument' questions, look for how a sentence bridges the gap between a premise and the final conclusion. Here, it functions as a premise that facilitates the transition from the microscopic level to the macroscopic level of the ecosystem.