Antarctic krill (Euphausia superba)—tiny yet mighty crustaceans—are key players in the Southern Ocean ecosystem. While they are known to respond to environmental cues like light and food, groundbreaking research now reveals that these krill also rely on internal biological clocks to survive in the harsh polar climate.
What Are Antarctic Krill?
Antarctic krill are small, transparent crustaceans that grow up to six centimeters in length and weigh around two grams. Despite their tiny size, they form massive swarms spanning several square kilometers, serving as a crucial food source for whales, seals, penguins, and fish.
Their behavior—especially their daily vertical migration—has long fascinated scientists. Krill rise to the ocean surface at night to feed and descend during the day to avoid predators. But what exactly governs this movement?
Internal Biological Clocks Regulate Krill Migration
A collaborative study led by researchers from Julius-Maximilians-Universität Würzburg (JMU), the Alfred Wegener Institute (AWI), the Helmholtz Institute for Functional Marine Biodiversity (HIFMB), and the UK’s National Oceanography Institute has provided new insights into this mystery.
Published in the journal eLife, the research shows that krill don’t rely solely on external cues like light. Instead, they use circadian rhythms—internal clocks—to regulate their daily swimming patterns, even under extreme polar conditions.
New Technology Tracks Individual Krill Behavior
In 2024, scientists developed a specialized activity monitor capable of tracking the movements of individual krill in seawater-filled tubes. Using this device, first author Lukas Hüppe, a doctoral researcher at JMU, studied wild-caught krill under varying light conditions and seasons.
The results were clear: krill exhibited higher swimming activity at night, mimicking their natural migration behavior. Remarkably, even when kept in constant darkness for several days, the krill continued to follow a daily activity rhythm—solid evidence that their movements are guided by an internal circadian clock.
Adapting to Polar Extremes
These findings suggest that Antarctic krill can adapt to extreme seasonal changes in daylight, a necessity for survival in the polar regions, where day and night lengths vary dramatically throughout the year.
“Krill don’t just respond to environmental changes like light or food—they actively use internal biological clocks to synchronize with their surroundings,” explains senior researcher Charlotte Förster.
Why This Matters: Ecosystem and Climate Impacts
Understanding krill behavior isn’t just about marine biology—it has global implications. Krill play a central role in the Southern Ocean carbon cycle, helping sequester carbon from the surface to the deep sea. This makes them essential to Earth’s climate regulation.
“The Southern Ocean is a critical carbon sink, and krill are at the heart of this ecosystem,” says Bettina Meyer from AWI and HIFMB.
Healthy krill populations are essential for maintaining the ocean’s ability to combat climate change. A deeper understanding of their adaptive behaviors helps researchers predict the impact of environmental changes on marine biodiversity and global carbon cycles.
What’s Next? Exploring the Krill Brain Clock
In future studies, researchers aim to pinpoint the exact location and mechanism of the internal clock in the krill brain. They also plan to explore how this clock influences other biological processes, including reproduction and hibernation strategies.
📘 Reference
Hüppe, L. et al. (2025). A circadian clock drives behavioral activity in Antarctic krill (Euphausia superba) and provides a potential mechanism for seasonal timing. eLife. DOI: 10.7554/eLife.103096.3