Diel vertical migration

[9] While this mass migration is generally nocturnal, with the animals ascending from the depths at nightfall and descending at sunrise, the timing can alter in response to the different cues and stimuli that trigger it.

[13] The common swift is an exception among birds in that it ascends and descends into high altitudes at dusk and dawn, similar to the vertical migration of aquatic lifeforms.

[4][14] During World War II the U.S. Navy was taking sonar readings of the ocean when they discovered the deep scattering layer (DSL).

While performing sound propagation experiments, the University of California's Division of War Research (UCDWR) consistently had results of the echo-sounder that showed a distinct reverberation that they attributed to mid-water layer scattering agents.

Working with the UCDWR, the Scripps researchers were able to confirm that the observed reverberations from the echo-sounder were in fact related to the diel vertical migration of marine animals.

These migrations may have substantial effects on mesopredators and apex predators by modulating the concentration and accessibility of their prey (e.g., impacts on the foraging behavior of pinnipeds[16]).

[8] Reverse migration occurs with organisms ascending to the surface at sunrise and remaining high in the water column throughout the day until descending with the setting sun.

Normal diel vertical migration occurs in species of foraminifera throughout the year in the polar regions; however, during the midnight sun, no differential light cues exist so they remain at the surface to feed upon the abundant phytoplankton, or to facilitate photosynthesis by their symbionts.

[4] Larger seasonally-migrating zooplankton such as overwintering copepods have been shown to transport a substantial amount of carbon to the deep ocean through a process known as the lipid pump.

[18] These copepods accumulate these lipids during late summer and autumn before descending to the deep to overwinter in response to reduced primary production and harsh conditions at the surface.

This is possibly due to increasing body size of the copepods and the associated risk of visual predators, like fish, as being larger makes them more noticeable.

[9] Evidence of circadian rhythms controlling DVM, metabolism, and even gene expression have been found in copepod species, Calanus finmarchicus.

[24] Changes in salinity may promote organism to seek out more suitable waters if they happen to be stenohaline or unequipped to handle regulating their osmotic pressure.

Areas that are impacted by tidal cycles accompanied by salinity changes, estuaries for example, may see vertical migration in some species of zooplankton.

Many zooplankton will react to increased pressure with positive phototaxis, a negative geotaxis, and/or a kinetic response that results in ascending in the water column.

Likewise, when there is a decrease in pressure, the zoo plankton respond by passively sinking or active downward swimming to descend in the water column.

It is possible that varying factors with the tides may be the true trigger for the migration rather than the movement of the water itself, like the salinity or minute pressure changes.

For example, the northern krill Meganyctiphanes norvegica undergoes diel vertical migration to avoid planktivorous fish.

Groups of smaller, harder to see animals begin their upward migration before larger, easier to see species, consistent with the idea that detectability by visual predators is a key issue.

Squid are a primary prey for Risso's dolphins (Grampus griseus), an air-breathing predator, but one that relies on acoustic rather than visual information to hunt.

Studies indicate that male dogfish (Scyliorhinus canicula) follow a "hunt warm - rest cool" strategy that enables them to lower their daily energy costs.

[35][36] A theory known as the “transparency-regulator hypothesis" predicts that "the relative roles of UV and visual predation pressure will vary systematically across a gradient of lake transparency.

For example, the occurrence of midnight sun in the Arctic induces changes to planktonic life that would normally perform DVM with a 24-hour night and day cycle.

[10] Species of foraminifera found in the ocean have been observed to cease their DVM pattern, and rather remain at the surface in favor of feeding on the phytoplankton.

[12] The biological pump is the conversion of CO2 and inorganic nutrients by plant photosynthesis into particulate organic matter in the euphotic zone and transference to the deeper ocean.

Because a large majority of the deep sea, especially marine microbes, depends on nutrients falling down, the quicker they can reach the ocean floor the better.

[18] Through overwintering, these lipids are transported to the deep in autumn and are metabolized at depths below the thermocline through winter before the copepods rise to the surface in the spring.

[18] The metabolism of these lipids reduces this POC at depth while producing CO2 as a waste product, ultimately serving as a potentially significant contributor to oceanic carbon sequestration.