Diel vertical migration
Encyclopedia
Diel vertical migration, also known as diurnal vertical migration, is a pattern of movement that some organisms living in the ocean
and in lakes undertake each day. Usually organisms move up to the epipelagic zone at night and return to the mesopelagic
zone of the oceans or to the hypolimnion
zone of lakes during the day. The word diel comes from the Latin
dies day
, and means a 24-hour period.
(DSL). The DSL was caused by large groupings of organisms that scattered the sonar to create a false or second bottom. The false bottom was shallower during the day and deeper during the night; this was the first recording of diel vertical migration.
Once scientists started to do more research on what was causing the DSL, it was discovered that a large range of organisms were vertically migrating. Most types of plankton
and some types of nekton
(fish) have exhibited some type of vertical migration, although it is not always diel.
and exogenous
. Endogenous factors originate from the organism itself; sex, age, biological rhythms, etc. Exogenous factors are environmental factors acting on the organism such as light, gravity, oxygen, temperature, predator-prey interactions, etc.
is the conversion of CO2 and inorganic nutrients by plant photosynthesis into particulate
organic matter in the euphotic zone and transferred to the deeper ocean. This is a major process in the ocean and without vertical migration it wouldn’t be nearly as efficient. The deep ocean gets most of its nutrients from higher up in the water column and it sinks down in the form of marine snow
. Marine snow is made up of dead or dying animals and microbes, fecal matter, sand, and other inorganic material. Fecal matter is what vertical migration helps get to depth much faster.
Organisms migrate up to feed at night so when they migrate back to depth during the day they defecate large sinking fecal pellets. Whilst some larger fecal pellets can sink quite fast, the speed that organisms move back to depth is still faster. At night organisms are in the top 100 metres of the water column but during the day they move down to between 800–1000 meters. If organisms were to defecate at the surface it would take the fecal pellets days to reach the depth that they reach in a matter of hours. Therefore by releasing fecal pellets at depth they have almost 1000 metres less to travel to get to the deep ocean. This is something known as active transport
. The organisms are playing a more active role in moving organic matter down to depths. 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.
Zooplankton
and salps are to play a large role in the active transport of fecal pellets. 15-50% of zooplankton biomass above 15-50% is estimated to vertically migrate and this can account for the transport of 5-45% of Particulate Organic Nitrogen to depth. As for salps, they are large gelatinous plankton that can vertically migrate 800 meters and eat large amounts of food at the surface. They also have a very long gut retention time so fecal pellets usually are released at maximum depth. Salps are also known for having some of the largest fecal pellets. Because of this they have a very fast sinking rate and small detritus
particles are known to aggregate on them. This makes them sink that much faster. So while currently there is still a lot of research being done on why organisms vertically migrate, it is very clear that vertical migration plays a large role in the active transport of dissolved organic matter to depth.
Ocean
An ocean is a major body of saline water, and a principal component of the hydrosphere. Approximately 71% of the Earth's surface is covered by ocean, a continuous body of water that is customarily divided into several principal oceans and smaller seas.More than half of this area is over 3,000...
and in lakes undertake each day. Usually organisms move up to the epipelagic zone at night and return to the mesopelagic
Mesopelagic
The mesopelagic is that part of the pelagic zone that extends from a depth of 200 to 1000 metres below the ocean surface. It lies between the photic epipelagic above and the aphotic bathypelagic below, where there is no light at all...
zone of the oceans or to the hypolimnion
Hypolimnion
The hypolimnion is the dense, bottom layer of water in a thermally-stratified lake. It is the layer that lies below the thermocline.Typically the hypolimnion is the coldest layer of a lake in summer, and the warmest layer during winter...
zone of lakes during the day. The word diel comes from the Latin
Latin
Latin is an Italic language originally spoken in Latium and Ancient Rome. It, along with most European languages, is a descendant of the ancient Proto-Indo-European language. Although it is considered a dead language, a number of scholars and members of the Christian clergy speak it fluently, and...
dies day
Day
A day is a unit of time, commonly defined as an interval equal to 24 hours. It also can mean that portion of the full day during which a location is illuminated by the light of the sun...
, and means a 24-hour period.
Discovery
During World War II the Navy was taking sonar readings of the ocean when they discovered the deep scattering layerDeep scattering layer
The deep scattering layer, sometimes referred to as "The Sound Scattering Layer"; is the name given to a layer in the ocean consisting of a variety of marine animals. It was discovered through the use of sonar, as ships found a layer that scattered the sound and was thus sometimes mistaken for the...
(DSL). The DSL was caused by large groupings of organisms that scattered the sonar to create a false or second bottom. The false bottom was shallower during the day and deeper during the night; this was the first recording of diel vertical migration.
Once scientists started to do more research on what was causing the DSL, it was discovered that a large range of organisms were vertically migrating. Most types of plankton
Plankton
Plankton are any drifting organisms that inhabit the pelagic zone of oceans, seas, or bodies of fresh water. That is, plankton are defined by their ecological niche rather than phylogenetic or taxonomic classification...
and some types of nekton
Nekton
Nekton refers to the aggregate of actively swimming aquatic organisms in a body of water able to move independently of water currents....
(fish) have exhibited some type of vertical migration, although it is not always diel.
Types and stimuli of vertical migration
There are two different factors that are known to play a role in vertical migration, endogenousEndogenous
Endogenous substances are those that originate from within an organism, tissue, or cell. Endogenous retroviruses are caused by ancient infections of germ cells in humans, mammals and other vertebrates...
and exogenous
Exogenous
Exogenous refers to an action or object coming from outside a system. It is the opposite of endogenous, something generated from within the system....
. Endogenous factors originate from the organism itself; sex, age, biological rhythms, etc. Exogenous factors are environmental factors acting on the organism such as light, gravity, oxygen, temperature, predator-prey interactions, etc.
Endogenous factors
- Endogenous rhythm- An experiment was done at the Scripps Oceanographic Research Institute which kept organisms in column tanks with light/dark cycles. A few days later the light was changed to a constant low light and the organisms still displayed diel vertical migration. Thus suggestions that some type of internal response was causing the migration.
Exogenous factors
- Light - An organisms wants to find an optimum light intensity (isolume). Whether it is no light or a large amount of light, an organism will travel to where it is most comfortable. Studies have shown that during a full moon organisms will not migrate up as far or during an eclipse they will start to migrate.
- Temperature - sometimes thermoclineThermoclineA thermocline is a thin but distinct layer in a large body of fluid , in which temperature changes more rapidly with depth than it does in the layers above or below...
s can act as a barrier that an organism will not cross. - Salinity - in areas such as the Arctic melting ice causes a layer of freshwater which organisms cannot cross.
- Predator kairomones - a predator might release a chemical cue which could cause its prey to vertically migrate away.
Types of vertical migration
- Diel - This has already been mentioned and is the most common form. Organisms migrate daily, usually up to shallow waters at night and deep waters during the day. But there are other forms of vertical migration worth mentioning.
- Seasonal - Organisms are found at different depths depending on what season it is.
- Ontogentic - Organisms spend different stages of their life cycle at different depths.
Reasons to vertically migrate
There are a lot of hypotheses on why organisms would vertically migrate. Each of these hypotheses are equally valid and most of the time more than one of the hypothesis account for a reason a species would vertical migrate.- Predator avoidance - Organisms come up to shallow waters at night to feed while it’s dark out because their predators cannot see them as easily.
- Metabolic Advantages - By feeding in the warm surface waters at night and residing in the cooler deep waters during the day they can conserve energy. Alternatively, organisms feeding on the bottom in cold water during the day may migrate to surface waters at night in order to digest their meal at warmer temperatures.
- Dispersal and Transport - Organisms can use deep and shallow currents to find food patches or to maintain a geographical location.
- Avoid UV Damage - The sunlight can penetrate into the water column. If an organism, especially something small like a microbe, is too close to the surface the UV can actually damage them. So they would want to avoid getting too close to the surface, especially during daylight.
Importance with the biological pump
The biological pumpBiological pump
In oceanic biogeochemistry, the biological pump is the sum of a suite of biologically-mediated processes that transport carbon from the surface euphotic zone to the ocean's interior.-Overview:...
is the conversion of CO2 and inorganic nutrients by plant photosynthesis into particulate
Particle (ecology)
In marine and freshwater ecology, a particle is a small object. Particles can remain in suspension in the ocean or freshwater, however they eventually settle and accumulate as sediment. Some can enter the atmosphere through wave action where they can act as cloud condensation nuclei...
organic matter in the euphotic zone and transferred to the deeper ocean. This is a major process in the ocean and without vertical migration it wouldn’t be nearly as efficient. The deep ocean gets most of its nutrients from higher up in the water column and it sinks down in the form of marine snow
Marine snow
In the deep ocean, marine snow is a continuous shower of mostly organic detritus falling from the upper layers of the water column. It is a significant means of exporting energy from the light-rich photic zone to the aphotic zone below. The term was first coined by the explorer William Beebe as he...
. Marine snow is made up of dead or dying animals and microbes, fecal matter, sand, and other inorganic material. Fecal matter is what vertical migration helps get to depth much faster.
Organisms migrate up to feed at night so when they migrate back to depth during the day they defecate large sinking fecal pellets. Whilst some larger fecal pellets can sink quite fast, the speed that organisms move back to depth is still faster. At night organisms are in the top 100 metres of the water column but during the day they move down to between 800–1000 meters. If organisms were to defecate at the surface it would take the fecal pellets days to reach the depth that they reach in a matter of hours. Therefore by releasing fecal pellets at depth they have almost 1000 metres less to travel to get to the deep ocean. This is something known as active transport
Active transport
Active transport is the movement of a substance against its concentration gradient . In all cells, this is usually concerned with accumulating high concentrations of molecules that the cell needs, such as ions, glucose, and amino acids. If the process uses chemical energy, such as from adenosine...
. The organisms are playing a more active role in moving organic matter down to depths. 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.
Zooplankton
Zooplankton
Zooplankton are heterotrophic plankton. Plankton are organisms drifting in oceans, seas, and bodies of fresh water. The word "zooplankton" is derived from the Greek zoon , meaning "animal", and , meaning "wanderer" or "drifter"...
and salps are to play a large role in the active transport of fecal pellets. 15-50% of zooplankton biomass above 15-50% is estimated to vertically migrate and this can account for the transport of 5-45% of Particulate Organic Nitrogen to depth. As for salps, they are large gelatinous plankton that can vertically migrate 800 meters and eat large amounts of food at the surface. They also have a very long gut retention time so fecal pellets usually are released at maximum depth. Salps are also known for having some of the largest fecal pellets. Because of this they have a very fast sinking rate and small detritus
Detritus
Detritus is a biological term used to describe dead or waste organic material.Detritus may also refer to:* Detritus , a geological term used to describe the particles of rock produced by weathering...
particles are known to aggregate on them. This makes them sink that much faster. So while currently there is still a lot of research being done on why organisms vertically migrate, it is very clear that vertical migration plays a large role in the active transport of dissolved organic matter to depth.