Hormone that govern sleep and jet lag in humans also drives mass migration of plankton.
Melatonin Signaling Controls Circadian Swimming
Behavior in Marine Zooplankton
Melatonin, the hormone that governs sleep and jet lag in humans, has been observed to drive mass migration of plankton in the ocean. Melatonin is essential to maintain our daily rhythm and scientists have now discovered that it governs the nightly migration of a plankton species from the surface to deeper waters.
This study comes from the marine rag worm Platynereis dumerilii where scientists discovered the planet’s biggest migration, in terms of biomass, by this worm’s larvae.
“We found that a group of multitasking cells in the brains of these larvae that sense light also run an internal clock and make melatonin at night. So we think that melatonin is the message these cells produce at night to regulate the activity of other neurons that ultimately drive day-night rhythmic behaviour.”
The night-time production of melatonin cause the larva’s cilia to take long pauses from spinning. These extended pauses cause the larva to slowly sink. During the day, when no melatonin is produced, the cilia are in full motion keeping the larva near the surface.
The work suggests that the light-sensing, melatonin-producing cells at the heart of this larva’s nightly migration have evolutionary relatives in the human brain. This implies that the cells that control our rhythms of sleep and wakefulness may have first evolved in the ocean, hundreds of millions of years ago.
My personal opinion
While the article leaves the reader pondering about the possible benefit of going to darker areas at night one possible reason for this mechanism could be to conserve energy. The cilia rotation is needed to keep the larvae near the surface during the day, but at night, with no sunlight, there is simply no need to expend much needed energy to keep itself near the surface.