Diel vertical migration

Lore & Background

Ernst Haeckel first gave the phenomenon its name in 1889, noting that planktonic organisms rose to the surface at night and sank by day. For decades the observation remained a curiosity of natural-history collecting. The picture changed dramatically during the Second World War, when sonar operators on Allied vessels reported a persistent, undulating 'layer' of echoes hundreds of metres below the hull that rose and fell with the sun. That signature—the Deep Scattering Layer—proved that DVM was not a quirk of a few species but a planet-scale, multi-taxon synchronisation.

Modern oceanography places DVM at the heart of two major biogeochemical cycles. The nightly ascent brings organisms into contact with surface phytoplankton and atmospheric CO₂; the daytime descent exports that carbon, along with faecal pellets and mucus, into the deep sea. Models of the biological carbon pump now treat DVM as a primary conveyor rather than a background process. At the same time, the migration creates a moving, three-dimensional feeding arena that structures the foraging behaviour of tuna, marlin, sperm whales, and countless other pelagic predators.

The phenomenon is remarkably robust. It has been documented in tropical, temperate, and polar waters; in open ocean, coastal shelves, and even some deep lakes. Disruptions—such as artificial light pollution along coastlines or rapid climate-driven changes in thermocline depth—are now recognised as potential stressors that could decouple the migration from the light cycle, with cascading effects on fisheries and carbon sequestration.

Reader's Guide

Imagine you are standing on the deck of a research vessel at dusk, watching the echo-sounder screen. The Deep Scattering Layer sits as a bright, undulating band roughly three hundred metres below the keel. As the sun drops, the band begins to climb—slowly at first, then with a steady, almost mechanical rhythm. You are watching millions of organisms—copepods, krill, larvaceans, small lanternfish—ascending in a coordinated wave, drawn upward by the fading light and the promise of phytoplankton-rich surface water.

At night, if you could see them, the scene would be a slow, shimmering rain moving upward. Krill pulse their pleopods in gentle strokes. Copepods execute short, ballistic jumps. Small fish hover in loose, drifting clusters, mouths opening and closing as they filter-feed. The whole column glows faintly with bioluminescence—blue-green sparks from dinoflagellates disturbed by passing bodies, the steady photophore glow of lanternfish.

Then the sun returns. The ascent stops. The column reverses. Organisms turn, orient downward, and sink. Copepods fold their legs. Krill stop pulsing and let gravity do the work. Fish tilt their bodies and glide down in long, silent spirals. Within an hour the layer has dropped back to its daytime depth, and the surface is empty again. The sonar band on your screen has settled, and the ocean looks, to the untrained eye, perfectly still.

Did You Know?

• The Deep Scattering Layer was first noticed as an anomaly by sonar operators during World War II, long before its biological cause was fully understood.
• Ernst Haeckel named and described the daily rise-and-fall of plankton in 1889, making DVM one of the earliest documented large-scale animal migrations.
• DVM is now considered a primary driver of the biological carbon pump, transporting organic carbon and CO₂ from the sunlit surface to the deep ocean every single night.
• The migration is so pervasive that it has been recorded in tropical, temperate, and polar oceans as well as in some deep freshwater lakes.