Question

baleen whales eat up to 30 percent of their total body mass in krill (tiny shrimplike creatures) per day. so in one day, a humpback whale weighing 30,000 kg could eat 9,000 kg, while a southern right whale weighing 80,000 kg could ingest a whopping 24,000 kg. over the last century, baleen whale populations have declined, and contrary to some scientists expectations, so have krill populations. matthew s. savoca and colleagues resolve this apparent discrepancy by pointing out that baleen whales cycle iron in the ocean, helping support phytoplankton populations, which, in turn, sustain krill populations. based on the text, what is one likely effect of the change in baleen whale populations over the last century? a the maximum body sizes of humpback and southern right whales have increased over the last century. b the quantity of krill needed to support a single southern right whale has increased over the last century c the iron richness of the krill that baleen whales eat has declined over the last century. d populations of phytoplankton that krill fed on have declined over the last century

Explanation:

The text states that baleen whales cycle iron in the ocean, supporting phytoplankton populations which sustain krill. Since baleen whale populations declined, phytoplankton (which krill depend on) would likely decline.

• Option A: No mention of body size increase in text.
• Option B: Text doesn't say krill quantity per whale increased.
• Option C: No info on iron richness of krill.
• Option D: Aligns with the chain (whale decline → less iron cycling → less phytoplankton support → phytoplankton decline).

Answer:

D. Populations of phytoplankton that krill fed on have declined over the last century.