What If Gone

Species → Antarctic krill

Antarctic krill

Euphausia superba

379,000,000 tonnes of total biomass (estimate)
Extinction risk Least Concern
Marine environmentKeystone speciesClimate changeNutrient cycling
Antarctic krill (Euphausia superba)
Photo: Wayne Trivelpiece, Wikimedia Commons (Public domain)

What if it disappeared?

Impact Major
Since the 1920s

The center of krill distribution has shifted about 440 kilometers south since the 1920s, tracking the warming of surface waters — a shift measured directly, independent of the whaling question.

Documented
Detail

Atkinson, A., Hill, S.L., Pakhomov, E.A. et al. (2019). Krill (Euphausia superba) distribution contracts southward during rapid regional warming. Nature Climate Change, 9, 142–147.

This southward contraction threatens to reduce the area of favorable krill habitat by about 30% by the end of the century, according to projections by the same authors — a stress that adds to, rather than replaces, the historical effects of whaling on the ecosystem.

Over several decades

By eliminating most large baleen whales — krill's main predators — industrial whaling was modeled to have produced a roughly 12% increase in available krill biomass, which penguins (+17%) and seals (+12%) were then able to take advantage of: this is the "krill surplus" hypothesis.

Documented
Detail

Surma, S., Pakhomov, E.A. et Pitcher, T.J. (2014). Effects of Whaling on the Structure of the Southern Ocean Food Web: Insights on the Krill Surplus from Ecosystem Modelling. PLoS ONE, 9(12), e114978.

An ecosystem model of the Southern Ocean simulating the removal of rorquals by 20th-century whaling. Absent changes in primary productivity, the model does indeed predict a krill surplus benefiting other predators — confirming, through modeling, a hypothesis already proposed from field observations.

Over 20 years

The benefit of the "surplus" proved temporary: a marked decline in Southern Ocean primary productivity over this period eventually outweighed the effect of reduced predation, triggering a cascading decline across nearly every group in the ecosystem — and the authors suggest that the disappearance of the whales themselves may have contributed to it, by reducing the iron recycling they provide through their iron-rich feces.

Documented
Detail

Surma, Pakhomov & Pitcher (2014), même étude — scénario complet intégrant le déclin de productivité primaire de 1975-1995.

It's a seemingly paradoxical feedback loop: fewer whales should, in the short term, leave more krill available for other predators; but fewer whales also means less iron recycled to the ocean surface through their feces, less phytoplankton, and therefore less food for krill itself in the longer term — a mechanism that may have neutralized part of the initial "surplus."

Coming decades

If the return of whales restores some of the iron recycling lost in the 20th century, this could ease the productivity decline that neutralized the krill "surplus" — but no one has measured whether this benefit can occur fast enough to offset the range contraction of krill caused by warming.

Extrapolated
Detail

Extrapolation combinant Surma et al. (2014) et Atkinson et al. (2019), qui documentent chacun un mécanisme distinct sans les mettre en balance l'un par rapport à l'autre sur la période actuelle.

Antarctic krill is a rare case in this repository where two well-documented mechanisms pull in opposite directions at the same time: whale recovery could work in its favor (recycled iron) while warming works against it (contracting habitat). Which of the two dominates over the course of the century remains to be established.

What's missing to confirm it: No study directly combines the effect of whale population recovery with that of warming to project the net trajectory of krill biomass in the 21st century.

Documentation

Last verified: August 14, 2026

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