The study, recently published in the journal Nature, found that giant baleen whales (such as blue whales, fin whales, and humpback whales) eat, on average, three times as much food each year as scientists had previously estimated.

As a result of this underestimation, scientists may have also previously underestimated the importance of these undersea giants to the marine ecosystem.

An adult blue whale may eat 16 tons of krill per day during the feeding season, the study found. A bowhead whale swallows about 6 tons of krill and small zooplankton per day. As generally understood, the number of predators and the number of prey should be inversely proportional. If the number of predators decreases, then the number of prey eaten also decreases and the number of prey should increase. But from 1910 to 1970, humans killed about 1.5 million baleen whales in the frigid waters that surround Antarctica, but at the same time, the abundance of small animals like krill declined. This is irrational.

The team suggests a possible ecological model to explain the phenomenon. The Southern Ocean is one of the most productive ecosystems on Earth, largely due to the presence of large amounts of phytoplankton - mostly microscopic algae. Phytoplankton are an important food source for krill, small fish, and crustaceans, which must be on the surface to photosynthesize, but seawater is so low in dissolved iron that phytoplankton can't proliferate.

Whales eat a lot, so they poop a lot. Through their activities of catching food and excreting feces, whales keep a lot of key nutrients suspended close to the surface of the ocean. Those huge quantities of whale feces contain about 10 million times the amount of iron found in Antarctic seawater, and it's this key factor that makes whales a central member of the Southern Ocean ecosystem. Iron is so scarce in the vast Southern Ocean that the whales' massive feeding and defecating behaviors take place in all corners of the sea, fertilizing all parts of the Southern Ocean, which greatly contributes to the ocean's productivity.

Researchers have calculated that whale populations before large-scale whaling in the 20th century produced about 12,000 tons of iron in their feces each year, 10 times the amount currently produced by whales in the Southern Ocean. The ecological function of phytoplankton is not limited to supplying krill; the large amount of photosynthesis also absorbs carbon dioxide from the atmosphere.

The researchers believe that if whale populations can be restored, they can greatly increase the amount of phytoplankton, which absorbs and fixes roughly 215 million tons of carbon into marine ecosystems and organisms each year. The findings suggest that whales' contribution to global productivity and carbon removal may be comparable to that of an entire continent's forest ecosystems. Helping whale populations recover restores lost ecosystem function, a natural climate solution.