The Ocean’s Greatest Migration Happens Every Night: Trillions of Animals Travel Vertically

Home Biology The Ocean’s Greatest Migration Happens Every Night: Trillions of Animals Travel Vertically

Biology

By Chuvic - July 16, 2025

Every night, as sunlight fades from the ocean’s surface, an astonishing natural event unfolds beneath the waves. Trillions of marine creatures—ranging from tiny zooplankton to larger fish and squid—begin a synchronized vertical migration, rising from the depths to feed near the surface before descending again at dawn. This phenomenon, known as the diel vertical migration, is not only the largest animal migration on Earth by sheer numbers but also a vital process shaping marine ecosystems. Its impact ripples through food webs and plays a crucial role in Earth’s carbon cycle.

NEXT >>

1. Diel Vertical Migration: Nature’s Nightly Commute

The Ocean’s Greatest Migration Happens Every Night: Trillions of Animals Travel Vertically — A mesmerizing scene of plankton rising through deep blue waters, capturing their daily vertical migration and bustling marine commute. | Generated by Google Gemini

Diel vertical migration is a rhythmic journey performed by countless ocean dwellers each night. As darkness descends, organisms such as copepods, krill, and lanternfish ascend hundreds of meters from the twilight zone toward the surface to feed on abundant phytoplankton and other prey. By dawn, these creatures retreat back to deeper, safer waters, effectively evading daytime predators. This daily commute is a masterful adaptation to the dual demands of hunger and survival, and it represents one of nature’s most efficient strategies for balancing risk and reward in the open ocean.

<< Previous

NEXT >>

2. The Twilight Zone: Migration’s Hidden Highway

The ocean’s twilight zone, or mesopelagic layer, lies between 200 and 1,000 meters below the surface. This dimly lit realm is neither fully dark nor sunlit, making it a unique crossroads for marine life. Here, countless animals gather during daylight hours, shielded from surface predators. The twilight zone teems with biodiversity and serves as a critical highway for the nightly migration. Scientists are only beginning to understand its immense ecological importance, as this region harbors more fish biomass than all commercial fisheries combined.

<< Previous

NEXT >>

3. Who’s on the Move? Key Migrating Species

The nightly vertical migration is powered by a cast of remarkable marine species. Copepods and krill, tiny crustaceans, form the foundation of the oceanic food web and are among the most abundant participants. Lanternfish, famous for their bioluminescent glow, represent a significant portion of migrating biomass. Squid and jellyfish also join the ascent, hunting or feeding in the upper layers before returning to the depths. Each species plays a unique role, sustaining predators and shaping the dynamics of the marine ecosystem during this nightly journey.

<< Previous

NEXT >>

4. A Journey of Trillions: Unimaginable Scale

The scale of the ocean’s nightly migration is truly mind-boggling. Every dusk, trillions of creatures rise and fall in unison, representing the largest animal migration on the planet by sheer numbers. The combined biomass of these migrating animals far exceeds that of all terrestrial animal migrations, including the iconic wildebeest herds of Africa. Scientists estimate that lanternfish alone may number in the quadrillions, moving in massive, shimmering waves. This synchronized movement shapes nutrient distribution and energy flow throughout the ocean, making it an event of global ecological significance.

<< Previous

NEXT >>

5. Feeding Frenzy: Chasing Plankton

The nightly migration is largely fueled by the pursuit of plankton, which drift near the ocean’s surface under the cover of darkness. At night, phytoplankton and zooplankton become more abundant and accessible, sparking a feeding frenzy among migrating species. This rich food source draws countless animals upward, where they gorge before retreating to deeper waters at dawn. The cycle not only nourishes the migrators but also supports predators that follow them, creating a cascade of life that pulses through the ocean’s upper layers each and every night.

<< Previous

NEXT >>

6. Escaping the Light: Predator Avoidance

Survival drives the extraordinary vertical migration, as many marine animals use darkness as a cloak to evade predators. By ascending to feed only at night, creatures like krill and lanternfish avoid the prying eyes of visually hunting predators, such as fish, squid, and marine mammals, that dominate the sunlit surface by day. When daylight returns, these animals descend into the twilight zone’s relative safety, minimizing their risk of being seen and eaten. This behavioral adaptation is a striking example of how evolution shapes life in the ocean’s vast, open spaces.

<< Previous

NEXT >>

7. The Carbon Express: Moving Earth’s Carbon

Diel vertical migration is a powerful engine in Earth’s carbon cycle. As trillions of animals feed near the surface, they ingest carbon-rich plankton. When they descend to deeper waters, they transport this carbon with them, releasing it as waste or through respiration in the twilight zone. This process, known as the “biological pump,” helps sequester carbon away from the atmosphere, playing a critical role in regulating the planet’s climate. Read more at WHOI.

<< Previous

NEXT >>

8. Early Sonar Mysteries: The Deep Scattering Layer

When sonar technology was first used during World War II, operators noticed a puzzling phenomenon: a “false bottom” that shifted up and down each day. This mysterious layer was actually the dense congregation of migrating animals, which scatter sonar signals with their bodies. It became known as the deep scattering layer. For years, its true nature baffled scientists until further study revealed it was caused by the ocean’s vast, nightly migration. Smithsonian Magazine

<< Previous

NEXT >>

9. Lanternfish: Migration Superstars

Lanternfish are true superstars of the ocean’s nightly migration. Numbering in the trillions, they are among the most abundant vertebrates on the planet. These small, bioluminescent fish travel vast distances vertically each night, feeding near the surface and diving deep by day. Lanternfish play a critical role in the marine food web, serving as prey for larger fish, squid, and marine mammals. Their immense biomass and migratory behavior make them central to nutrient cycling and energy flow in the ocean. National Geographic

<< Previous

NEXT >>

10. Deep-Sea Squid: Agile Travelers

Deep-sea squid are among the ocean’s most agile and efficient migrators. Each night, these remarkable creatures propel themselves upward from the depths using jet propulsion—a rapid expulsion of water from their mantles—allowing them to cover hundreds of meters swiftly. Their speed and maneuverability help them evade predators while seeking prey near the surface. Squid play a vital role in the nightly migration, not only as hunters but also as prey for larger animals, further enriching the ocean’s complex food web and energy transfer.

<< Previous

NEXT >>

11. Jellyfish: Passive Migrators

Jellyfish are notable participants in the ocean’s nightly migration, though their approach is far more passive than that of fish or squid. Relying on slow, rhythmic pulsations and the movement of ocean currents, jellyfish gradually ascend toward the surface at night and descend by day. Their gelatinous bodies make them easy prey for faster, more agile migrators like lanternfish and squid. Despite their vulnerability, jellyfish play an important role in the food web, transferring nutrients and energy between different layers of the ocean.

<< Previous

NEXT >>

12. Predators on Patrol: Tuna and Swordfish

Large predators such as tuna and swordfish are expert hunters that take full advantage of the nightly vertical migration. As swarms of smaller animals ascend toward the surface, these agile predators follow, using the cover of darkness to ambush their prey. Tuna, in particular, are known for their speed and endurance, allowing them to pursue lanternfish, squid, and other migrators efficiently. This nightly feast is crucial for the survival and growth of top predators in the open ocean. NOAA Fisheries

<< Previous

NEXT >>

13. Light and Darkness: The Role of the Sun

The precise timing of the ocean’s vertical migration is dictated by the rising and setting of the sun. As daylight fades, animals sense the diminishing light and begin their ascent toward the surface. At sunrise, the first hints of returning light trigger a rapid descent into deeper, darker waters. This sensitivity to light ensures that migrators minimize their exposure to visual predators, optimizing both feeding opportunities and survival. The sun’s daily rhythm choreographs this remarkable dance between light, darkness, and the movement of countless marine creatures.

<< Previous

NEXT >>

14. Oxygen Minimum Zones: A Risky Refuge

Some migrating animals exploit the ocean’s oxygen minimum zones—midwater layers where oxygen levels are perilously low—as a refuge from predators. In these challenging environments, few large predators can survive, giving smaller species a temporary edge. However, staying in these zones is risky, as low oxygen also strains the animals’ own physiology. Migrators must carefully balance the benefits of safety with the dangers of suffocation, making their journey even more complex. MBARI

<< Previous

NEXT >>

15. The Microbial Connection

Microbes play an essential role in the aftermath of the ocean’s nightly migration. As migrating animals release waste or die in deeper waters, organic matter sinks and becomes food for deep-sea bacteria and other microorganisms. These microbes break down the material, recycling vital nutrients back into the ecosystem and supporting life even in the darkest ocean depths. This microbial activity creates a direct link between vertical migration and the deep-sea nutrient cycles, highlighting the interconnectedness of all life within the ocean.

<< Previous

NEXT >>

16. Migrating Mollusks: From Pteropods to Squid

Mollusks are another diverse group joining the ocean’s nightly ascent. Tiny pteropods, also known as “sea butterflies,” flutter upward with delicate wing-like appendages, while larger squids jet swiftly through the water. Each species migrates at different depths and speeds, adapting to their physiology and ecological niches. These mollusks are both predators and prey, playing pivotal roles in marine food webs and energy transfer. Their participation in diel vertical migration underscores the phenomenon’s remarkable diversity, spanning from minuscule drifting creatures to agile, deep-diving hunters.

<< Previous

NEXT >>

17. Krill: The Tiny Powerhouses

Krill are small, shrimp-like crustaceans that form some of the densest swarms on Earth. These tiny powerhouses are a cornerstone of marine ecosystems, providing a crucial food source for whales, fish, and seabirds. By migrating vertically each night, krill help transport nutrients from the surface to deeper waters, supporting the ocean’s nutrient cycles. Their massive numbers and central role in food webs make them indispensable to the balance of life in the sea. NOAA

<< Previous

NEXT >>

18. Fish Larvae: Early-Life Travelers

Fish larvae are among the youngest participants in diel vertical migration, and their nightly journeys are crucial for survival. By moving closer to the surface at night, larvae access rich feeding grounds while reducing their risk of being spotted by predators. This vertical movement helps them grow more quickly and disperse to new habitats, ultimately shaping both their chances of survival and the distribution of future fish populations. The migration habits established early in life echo throughout the broader marine ecosystem.

<< Previous

NEXT >>

19. The Migration’s Startling Speed

The speed of diel vertical migration is nothing short of remarkable. Some animals, such as lanternfish and squid, can travel several hundred meters vertically in less than an hour once darkness falls. This rapid ascent and descent make the migration one of the fastest mass movements in the natural world. The ability to cover such vast distances quickly is essential for feeding, avoiding predators, and synchronizing with the daily rhythm of the ocean, showcasing the extraordinary adaptability of these marine creatures.

<< Previous

NEXT >>

20. Acoustic Shadows: Hiding from Echolocators

In addition to visual predators, many marine animals must also contend with echolocating hunters such as dolphins and whales. Some migrators use clever strategies to avoid detection, including gathering in dense swarms that create confusing “acoustic shadows,” or descending to depths where sonar signals are less effective. These adaptations help reduce the risk of being singled out and hunted in the vast, dark ocean. The interplay between predator and prey in the soundscape of the sea is a fascinating chapter in the story of vertical migration. Science Advances

<< Previous

NEXT >>

21. Bioluminescence: Lighting the Way

Many species participating in the nightly migration possess the remarkable ability to produce their own light, a phenomenon known as bioluminescence. Lanternfish, jellyfish, and certain types of squid use glowing organs for various purposes—communicating with mates, confusing or deterring predators, and blending in with faint surface light to avoid detection from below. This dazzling display transforms the dark ocean into a living constellation, offering both beauty and survival advantages during the perilous journey through the depths each night.

<< Previous

NEXT >>

22. Ecosystem Impacts: Supporting Ocean Life

The nightly vertical migration is a cornerstone process in the world’s oceans, profoundly shaping marine ecosystems. As trillions of animals move up and down the water column, they actively redistribute nutrients between surface waters and the deep sea. This movement sustains complex food webs, feeding both surface predators and deep-sea scavengers. By transporting organic matter and facilitating nutrient cycling, the migration helps maintain the health and productivity of the entire marine environment. Woods Hole Oceanographic Institution

<< Previous

NEXT >>

23. Global Carbon Sink: Climate Implications

Diel vertical migration plays a crucial role in Earth’s climate system by acting as a natural carbon sink. As migrating animals transport carbon from the surface to deeper waters, they help sequester billions of tons of carbon each year. This process slows the buildup of atmospheric CO₂ and helps regulate global temperatures. Scientists continue to study this remarkable mechanism, recognizing its significance in mitigating climate change and maintaining planetary balance. Nature

<< Previous

NEXT >>

24. Human Impacts: Threats to the Migration

The delicate balance of diel vertical migration faces mounting threats from human activities. Climate change alters ocean temperatures and disrupts currents, while overfishing depletes key migratory species. Pollution, including plastics and chemical runoff, can harm marine organisms and degrade essential habitats. These disruptions threaten not only the migrating animals but also the broader ecological processes that sustain ocean health and regulate Earth’s climate. Protecting this nightly migration is vital for maintaining the resilience of marine ecosystems. NOAA Climate

<< Previous

NEXT >>

25. Technology’s Role: Studying the Migration

Modern technology is revolutionizing our understanding of diel vertical migration. Scientists now deploy advanced tools such as underwater robots, acoustic sensors, and satellite tracking to observe and measure the nightly movements of marine life. These innovations provide unprecedented insights into migration patterns, animal behavior, and ecosystem impacts, even in the ocean’s most inaccessible regions. By combining real-time data with new analytical techniques, researchers are unraveling the mysteries of this vast and vital phenomenon. MBARI

<< Previous

NEXT >>

26. Why It Matters: The Ocean’s Beating Heart

The nightly vertical migration is more than just a marvel of nature—it is the beating heart of the world’s oceans. By nourishing food webs, cycling nutrients, and sequestering carbon, this daily journey sustains ocean health and helps regulate Earth’s climate. Protecting this intricate process is essential for the resilience of not only marine ecosystems, but the planet as a whole. Continued research and conservation efforts ensure that the ocean’s greatest migration can thrive for generations to come, safeguarding the very systems that support life on Earth.

<< Previous