Plankton (sing. Plankter) is a diverse group of organisms that live in water and cannot swim against the water current. They are used as an important food source for a variety of aquatic organisms such as fish and whales. They are floating organism such as various animals, protists, archaea, algae or bacteria etc. and they live in the pelagic region of the sea, ocean or freshwater. Although many plankton species are microscopic in size, they include a variety of organisms, including large organisms such as jellyfish.
All types of natural reservoirs are suitable for most plankton habitat irrespective of longitude and latitude. Although they may vary from different perspectives
General Geographical Distribution of Plankton
Latitude Variation: Some oceanographers have long thought that Plankton abundance is higher in the tropical seas than in the polar seas. This doctrine is based on some incomplete information. That is why it has not gained universal acceptance. According to Allen (1939) phytoplankton is scarce in large areas of high latitude seas and phytoplankton is abundant in large areas of the tropical ocean. Some Arctic marine plankton are thought to be larger than warm-water relatives. This is due to thermal effects. However, the effect of heat on mass production of plankton is still unknown.
To date, lymphological data on polar and tropical inland waters have not been known, and comparative plankton production between them has not been satisfactorily reviewed. It is thought that the amount of plankton is less in the tropics than in the temperate zone. In the case of some northern low lakes in the countries bordering the Baltic Sea, it is assumed that a large number of plankton are produced here. However, it is not clear whether it is due to latitude or any other reason. Regular high alpine lakes produce small amounts of plankton. Very little is known about the production of plankton in inland waters in northern North America.
According to Raison (1947), plankton production is very low in Great Bear Lake, Great Slave Lake and Athabasca Lake. Almost entirely unknown to plankton in the tundra region. According to Shelford and Twomey (1941), a small amount of crustacean plankton is found in Lake Isabella in the tundra country near Churchill in July. The same is true of the west coast of Hudson Bay and Canada. Numerous members of Cladocera and some Protozoan plankton are found in small permanent ponds in the same region. Satisfactory comparison of plankton production of different latitudes could not be made due to lack of significant data. There is no conclusive evidence of higher plankton production in Arctic inland waters from the greater south.
Horizontal Distribution of Plankton
Uneven Distribution: One of the well-established principles of horizontal distribution of plankton over a large area is its irregular presence. In the early stages of the history of plankton research, it was thought that because the environmental conditions of the oceans were similar, the extent of plankton would be similar. However, it is now known that there is no basis for such an idea in the case of marine or freshwater.
Some of the methods of plankton research have changed due to the discovery of the irregular presence of plankton's horizontal distribution. Such a lack of equality is observed in relatively small lakes or lakes in addition to large areas. Such irregular presence of plankton proliferation is observed in both phytoplankton and zooplankton. However, some studies have shown greater similarity in the distribution of phytoplankton from zooplankton. Moreover, the presence of large-scale irregularities in the distribution of zooplankton is not related to the physico-chemical properties of the environment.
Reasons for Unequal Distribution
Wind action: One of the more common causes of uneven distribution of plankton in horizontal distribution is the action of wind on the surface of the reservoir. It is universally acknowledged that waves are one of the main currents of water in addition to air. In the case of flowing water, plankton are temporarily collected near the shore in some cases. At this time the speed of movement of plankton is towards the wind.
The floating plankton is widely seen in many lakes during the summer. Sometimes such floating plankton accumulates especially on the shore and the density of this plankton is so high that the color and general properties of all the water change. Due to the higher density of plankton, the surface of the water in the small bay becomes colorful at this time.
The movement of surface water disrupts the plankton's coexistence. As a result, plankton began to gather towards the shore. The general effect of such plankton migration is that the plankton becomes more or less concentrated on one side across the upper layer of the lake and decreases on the other side. Collecting plankton samples from near open shores results in higher than the average plankton density of the lake. Plankton density, on the other hand, would be lower than the average value if samples were collected from areas far from the shore. In this case, the sample should not be collected from the open shore. The surface plankton is more affected by the flow of water. The transfer of plankton occurs as a result of air flow. When the air flow stops or changes its direction, all the plankton that has accumulated goes back to normal. Part of the migrated plankton, especially when the coastal area is washed away, they move elsewhere. Again some part of the migrated plankton is accidentally mixed with the shore elements.
Incoming Streams: Incoming streams transfer water to the surface of the reservoir. As a result, different types of effects are created, e.g.
(1) The area around the mouth of the incoming river increases the quality, quantity or both of the plankton. In certain cases, some stagnant vegetated rivers associated with lakes have higher amounts of plankton than lakes, resulting in rich plankton in the connected lakes. In samples collected from opposite sides of such river mouths, the density of plankton exceeds the average density of the lake.
(2) Dilution: In most cases, the amount of plankton in the water coming from the river is less than the water in the lake. As a result, the density of plankton on the opposite side of the river mouth decreases. River tributaries (especially those that do not carry stagnant water in any way) contain small amounts of plankton. Many slow-moving rivers produce plankton less than lake water.
(3) Qualitative variation: Flowing rivers regularly carry plankton to the lake. Such plankton are not commonly produced in lakes.
Physico-chemical alteration of the water: The water of the river coming into the lake is physically different from the water of the lake. As a result, the water in the lake carries different types of plankton. Such plankton can destroy some of the local plankton of the lake.
Irregularity of shore line: Inequality is observed in the horizontal distribution of plankton due to irregular shore line. The inequality of the shoretline creates different types of seas and bays. Such seas and bays have a favorable environment for plankton production. An abundance of many species of plankton can be observed here. Such semi-open reservoirs provide adequate protection from the general flow of open water. As a result, it became a more or less sustainable plankton-rich region for plankton population.
Depth of water: Depth of water has a significant effect on the horizontal distribution of some plankton species. It has been observed that in some conditions and seasons the growth of diatoms is higher in deep water areas than in shallow water areas. This condition is also observed in a few other species of animals, especially in the immature stage of some fish.
General flowage areas: General flow areas, especially shallow water flow, in most cases change the horizontal distribution. If there is a major entrance and an outlet near the same lake, and a variety of other surrounding conditions produce the flow of the entire surface water, resulting in a wide variation in plankton distribution. This causes uneven distribution of plankton.
Current: Any type of current changes the general horizontal distribution of plankton in different ways. The density of plankton varies from the surrounding, more stable areas.
Undertow : A sudden strong wind blows a strong slope on one side of the lake causing reverse current and resulting in uneven distribution of plankton.
Plankton swarms: Oceanographers in most cases observe the formation of swarms of the local plankton population. Excessive density of some plankton species can sometimes be observed. The density of such local plankton communities is so high that it forms a certain color of water. Such incidents can be noticed in the lake. Such plankton swarms can be caused by the active migration of certain species to a particular favorable area of the lake or by the rapid reproduction of a species in a favorable area. Such swarms are formed due to the large number of members of the same species (such as some Cladocera, Protoza and others).
Action of predators: The swarm of plankton eaters greatly reduces the number of local plankton. Thus a group of predators devour a large number of plankton.
Indirect results of diurnal migration: Plankton's diurnal migration may indirectly play a role in their irregular horizontal migration. The nocturnal airflow changes the swarm of migratory plankton. As a result, many plankton are not able to go back into the water with the arrival of dawn. Thus the plankton get stuck in the surface water. In the changed state, plankton are waiting for the opportunity to return to deep water. As a result, they temporarily create inequality in horizontal distribution.
Due to the decrease in plankton towards the shores of the lake, in some cases, limnatic plankton sometimes accumulate towards the center of a lake. Such phenomena indirectly contribute to the vertical distribution of plankton in the following ways. All the plankton that migrates go down at the beginning of dawn. The broad plankton near the shore is moved to the bottom at a high rate and accumulates in the deep water below the slope of the basin to reach the deep water. Later they move to the surface of the water.
Vertical Distribution of Plankton
The vertical distribution of plankton is a complex matter. Plankton's quality and quantity, or both, vary in different types of horizontal layers. Plankton in the upper layers of water have little or no resemblance to plankton in the deepest region. In some deep regions, no actual plankton is ever found, and there may be occasional small amounts of plankton on the surface of the water. In the second class of lakes, only in spring and winter can the plankton's roughly similar vertical distribution be observed. Soon after, plankton's vertical distribution was re-established in different layers. In the case of third-class lakes, some variation is observed in the vertical spread of plankton during calm. However, in the action of air, the influence of currents shows that plankton tends to mix and form a uniform distribution. Moreover, general biological stratification is a feature of the overall population. As a rule, each plankton's own population can be identified by its maximum population. Some plankton extend slightly from the surface of the habitat to the lowest limit. A plankton-centered area is commonly observed in some places within this range of plankton distribution.
Distribution of Phytoplankton
Chlorophyll-containing phytoplankton can be observed up to the depth of the light penetration areas in a lake. Plankton is sometimes not found at that depth due to chemical stratification. For example, in a very clear lake, in a closed state in summer, light effectively enters a certain depth and reaches hypolimionion. However, if there is no oxygen at the top of the hypolipidemia and it is uninhabitable, the distribution of depth-based plankton is limited to a small area. The surface area of water is home to chlorophyll-rich plankton, but there are limitations in the distribution of plankton in the upper and lower areas of this general region. It is thought that the vertical distribution of plankton occurs in the following ways:
Distribution of Zooplankton
The factors controlling the vertical expansion of the zooplankton are so diverse that it is rarely possible to describe the vertical distribution. There are several trends in the vertical distribution of zooplankton, such as -
The type of plankton spread varies from the reservior to reservior. Physico-chemical stratification occurs obviously in special cases. The maximum populations of Crustacea and Rotifera are very close in most cases. Although there is distribution in some cases, Crustacea eat rotifera as food. The distribution of large groups of plankton changes with the change of seasons. The cold water zooplankton tends to spread to deeper areas. Plankton rises to the top when there is an oxygen-deprived area in the deepest region.
Relationship between physical and chemical stratification: Physico-chemical stratification is observed in lakes. The vertical distribution of plankton is profoundly affected by various factors of stratification. Plankton spreads throughout the reservoir as the temperature changes in the second-class lake. As the temperature in closed water bodies increases in summer, plankton gradually decreases and sometimes plankton is completely absent. On the other hand, intense concentration and microstructure of plankton sometimes results in the formation of thermocline layers. In many lakes, the amount of living plankton reaches its lowest point by the end of summer. At this time the thermocline level also reaches the lowest level. No significant plankton can be seen in the ground water. There is no plankton in deep water at certain times or in certain conditions. However, several types of bacteria can be seen in these places.
The vertical distribution of plankton is observed in the summer without currents. If this condition does not change, an equal expansion is observed everywhere with which there are some similarities between the summer tidal conditions. There is no effect of true thermocline here. Light relations change through ice and snow. The gravity of effective light penetration becomes more limited. It is thought that plankton, which carries chlorophyll, occupies a higher level. If the reservoir is frozen for a long time, a part of all types of plankton will be reduced.
Concentrated regions of plankton and low density regions: During thermal and chemical stratification, some plankton show a tendency for their population to accumulate in certain areas at certain depths. There are several such examples. This concentrated area can be wide. In contrast, the density of other plankton tends to be extremely low. It cannot be prevented without maintenance. In the case of plankton sampling, areas with low density are excluded, so population sampling is not included.
Factors that influence vertical distribution: The following are some of the factors that play an important role in the vertical distribution of different types of plankton:
- Dissolved gases especially oxygen and other dissolved gaseous components.
- Relative density
- Age of species members
(1) Light: Light has a significant effect on the vertical propagation of plankton. The presence of light reduces the amount of plankton in the surface of the water for various reasons. Sometimes plankton is completely absent. The deepest areas do not contain chlorophyll-containing plankton and many other plankton. The quality, quantity, annual, daily and other variations of light cause plankton to shift and change. The vertical distribution of plankton depends on the nature and thickness of the ice. Removing snow from the ice significantly changes the vertical distribution of many plankton. As a result more light enters.
Different types of plankton can be abundant in the upper layer of water below the ice. The reaction of light to the offspring and mature stages of some plankton has resulted in different vertical distribution in the life history of the same species. Such instances are commonly found in plankton of the Crustaca species. Some of these species mature / grow to a deeper level away from light. Immatures, however, react positively to light and occupy the surface of the water.
(2) Food: The relationship between food and eater can be deduced by explaining some of the phenomena of vertical distribution of plankton. The extent of such predators is somewhat determined by the extent of their food. Attempts have been made in the past to explain the density of protozoa, tiny crustaceans and rotifera in that layer by examining the sedimentary components of the thermocline layer and observing the temporal effects.
This suggests that at that level a higher density of those objects is created. This suggests that all of these elements mix with bacteria. Protozoa and other creatures take their food from there. As a result crustaceans and rotifers gather there to take protozoa and other ingredients as food. In the same way the presence of limnatic algae in the surface water is related to the spread of microcrystals. It is generally said that plankton are found in abundance where there is plenty of food.
(3) Dissolved gases especially oxygen and other dissolved gaseous elements: Chemical changes in water at the bottom create unfavorable conditions for plankton. Deep water becomes partially or completely uninhabitable for most plankton if there is a lack of dissolved oxygen, even if other elements are properly present. The disintegration effects of organic matter on the bottom of the water tend to be more sensitive to certain plankton than others. Not all upper plankton die as a result of certain stratification. Moreover chemical changes tend to be fatal for most or all types of plankton in most cases. As a result, plankton eventually became extinct from some of the lower layers.
(4) Relative density: The vertical position of many plankton is related to relative importance. Some phytoplankton, such as Gloeotrichia, are relatively important and are located on the surface of the water. On the other hand, many plankton, such as the Pelagic crustacean, move to the lower reaches of the reservoir with significant speed while being temporarily inactive due to being heavier than water. Daphnia regularly maintains their position in the water in the following ways:
In the short time of inactivity of their swimming appendages, the animal sinks about 20-30 cm per minute. They return to the surface of the water at the beginning of the swim by repeatedly hitting the antennae. Occasionally, there is a change in the horizontal spread through swimming. But quickly reaches a new position by swimming up and down in stages. As a result of regular energy expenditure, the animal (Daphnia) does not get a chance to rest. Other crustaceans such as Diaptomus, Cyclops and others are less mobile than Daphnia. Nevertheless, energy must be expended to maintain their position.
Organisms that grow older and larger in size (Daphnia and Cyclops) tend to have more energy as they age and at times weaker bodies. When they drown, small animals stand behind them. It is said that the rate of immersion of newly developed Daphnia from adult Daphnia is 1/3. So they need less energy to stay afloat against the force of gravity. Some other planktonic crustaceans, such as Diaptomus, Diaphanosoma, rarely drown due to the development of significant amounts of body fat. Thus most plankton float.
(5) Wind flow: With the change of seasons, the effect of wind flow also varies significantly. In summer it can only affect the epilimnion level. The vertical expansion of plankton may change during strong winds. However, such changes are not widespread. However, such vertical currents are temporarily generated because active plankton, especially crustaceans, are significantly independent. So they may react negatively.
The airflow causes movement at the thermocline level. This results in significant changes in the vertical position of different plankton layers. The opposite happens in autumn and spring. Air flow plays an important role in the expansion of plankton as the density and viscosity of water remain the same everywhere except for significant changes in temperature. During this time the water flow is extensive and most of the phytoplankton is produced. Plankton are widely distributed in water and various types of plankton are transferred vertically from the bottom to the summer. Air has no effect on the distribution of plankton when it is frozen. Some plankton, such as diatoms, float or sink at higher levels, but airflow can affect their vertical distribution at any time.
(6) Temperature: Temperature directly or indirectly affects the vertical distribution of plankton. The direct effect of temperature is usually seen in the following cases:
(i) Selection of some optimal temperature by some moving plankton.
(ii) Failure of certain immobile plankton to settle at certain temperature levels. Vertical distribution can be observed in plankton that are sensitive to temperature variations. Many plankton, on the other hand, are not affected by any kind of vertical temperature difference in a lake. The thermal properties of the thermocline layer are considered to be an excellent quality measure in determining the position of certain plankton. Temperature indirectly influences changes in density and viscosity. Such changes alter the floating level of the adaptive plankton in order to float smoothly. Moreover, it is thought that such conditions indirectly play a role in changing the light sensitivity of the lymphatic crustacean. Increases sensitivity at higher temperatures and decreases sensitivity at lower temperatures. Thus different levels of reactions are created.
(7) Age of members of the species: In the case of vertical distribution, specific differences have been observed between the offspring and adult stages of some plankton. Such a condition is most likely seen in plankton crustaceans. Some of their notable incidents are mentioned below:
-As a general rule, small (offspring) organisms in the form of a species live near the surface.
-The annual spring growth of the crustacean population consisting of the juvenile stage is more pronounced at the top of the water column.
-Older organisms are immersed in a deeper level.
-Nauplei certainly do not follow this rule, but in most cases their presence is observed in significant numbers near the thermoclinical region.
Diurnal movement of Plankton
A remarkable phenomenon of daily movement has been observed in the vertical movement of some notable plankton. This type of movement is seen in both sea and lake.
Daily migration of plankton: Large size plankton crustacea species migrate daily in inland water bodies. This type of movement is found in Cladocera and Copepoda. This type of movement is also seen in some ratifers. However, a small daily migration was observed in this group. An insect larva (Corethra) miraculously completes this migration. Such movements are observed to a limited extent in diatoms, flagellates and other organisms with poor mobility.
Nature and extent of daily migration: The daily migration of different species varies greatly in different environmental conditions. The following factors are partly responsible for daily maigration:
- The environmental conditions of the lake vary.
- Different types of plankton are not equally affected by these migration-controlling factors.
- The close relationship between plankton does not guarantee the smoothness of their movement.
- Members of the same species do not show the same behavior in different water bodies.
- The daily movements of Nauplei and other immature stages may differ from the older members of the same species.
The following important information is obtained from reports on the daily movement of different types of lakes in different geographical conditions:
Type-1: A part of the plankton population stays at the surface of the water at night, creating a wide vertical range of all populations without any general upward movement. During the day migratory plankton is not found in the water above. As a result, the population is concentrated in a more controlled area during the day. At night the density of all the populations decreases and they spread over a wide range.
Type 2: There are some plankton populations that live in or near the surface of the water at night and go deeper during the day.
Type-3: Some plankton in the hypolimonial layer move upwards, but thermocline becomes an obstacle for them.
Type 4: Most members of some Plankton population carry out daily movements on a small scale. However, few members move to the surface at night and return to the deepest part during the day.
Type-5: Some plankton come to the surface at dawn and dusk but live in deep water for the rest of the day and night.
Type-6: Some plankton species come to the surface in the afternoon but move at night with characteristic nocturnal movement.
Type-7: Some adult plankton members live near the surface of the reservoir day and night. Juvenile phase migrates into deep water in the morning.
Type-8: Some plankton offspring or juvenile phases go to or near the surface at night and live in groundwater during the day. However, their old age has the opposite effect.
From the above discussion it is understood that the same plankton exhibits more than one type of movement in different lakes and different environmental conditions. In the same way, in some cases, some plankton have more or less equal distribution in their special vertical range. If the daily vertical movement exists, the lake varies greatly up to a certain depth. Some plankton can only move less than one meter. The results of research on the maximum concentration of plankton on the surface of nocturnal water also vary widely. In some lakes, the maximum abundance of plankton can be observed on the surface of the water last night. In the case of the described type-5, the maximum abundance of plankton is seen between the two breaks, one at the beginning of the evening and the other very early in the morning.
Here are some common examples of the diurnal movement of zooplankton:
Corethra punctipennus (Culicidae, Diptera): It is a common inhabitant of the lakes of Central North America. Their larvae and pupae are aquatic. They perform diurnal movement miraculously in summer. During the day the larvae move into the mud at the bottom of deep water. However, the offspring larvae live in the water just above the bottom.
As evening falls, immature and mature larvae come to the surface of the water. Within an hour of sunset, they begin to reach the surface of the water, and the flow continues for some more time. They are abundant in surface water overnight. Not all larvae come from the bottom up. Generally 1/2 to 1/3 of the total larvae stay at the bottom. Just before sunrise, the larvae begin their journey from the surface of the water to the bottom. There are many instances of crossing the distance of 15 meters from the surface in 20 minutes and moving down. During the day, many of their larvae of Corethra plumicornis live on the surface of the water as well as on the bottom.
Leptodora kindtii (Cladocera, Crustacea): A significant transparent cladocera in the North American lake that rises to the surface of the water at night. Within 1-2 hours of sunset most of their members reach the surface. They disappear into deep water before sunrise. This species is found in significant quantities in some river parts, especially during the day. In areas where the water is clear and shallow, the species stays in the mud during the day.
Daphnia longispina (Cladocera, Crustacea): This cladoscera is a component of the plankton of lakes around the world. Researchers on several continents have studied this species. In some cases, thermocline has no effect on such plankton proliferation.
Similar migrations of Daphnia longispina can be seen in some tropical lakes such as Victoria and Nyanjar lakes. Daphnia longispina var., Despite the greater depth of some Winkonsin lakes. The Daphnia longispina var.hyalina has a vertical orientation of 0.2-6.0 m. In the case of Lake Lough Derge in Ireland, the offspring of Daphnia longispina move closer to the surface of the water at night and move closer to the bottom during the day. The opposite is true in the case of adult animals.
They move to illuminated areas during the day and to deep water at night. Reports from lakes and other places in Japan indicate that this species, Daphnia longispina, is confined to the hypolimnion level. At night they move upwards. However a single animal does not go above the thermocline region. Different types of cognitive behavior have been observed in different stages of Daphnia longispina. Some lakes, such as Lake Wisconsin, do not show daily movement. The pointed crested phase, on the other hand, exhibits such a movement. In Daphnia longispina, which has both structures in other lakes, the behavior is quite the opposite. In this case both the structured animals show daily movement.
Other Entomostraca: In some lakes of the crustacean plankton, the following species are seen daily in special conditions: Cladocera: Daphnia retrocurva, D. pulex, Diaphanosoma brachyurum, Bosmina longirostris, Polyphemus; Copepoda: Epischura locustris, Limnocalannus macsurus, some species of Diaptomus and Cyclops, Rotaria, Keratella (Anuraea), Cochlearis and Ploesoma and others.
Seasonal effects of daytime movement: Seasonal changes in temperate regions affect the daily movement of some plankton. However, the level of movement may vary between different species in different lakes. It is thought that as the winter progresses, the center of some plankton populations rises to the top. In winter, the daily movement is limited to a small range. Some species of Daphnia are thought to exhibit such behavior in some lakes.
During the hot summer months, the daily movement of plankton crustaceans, especially in some lakes in Europe, has been observed to decrease. It is assumed that the daily flow resumes when the water temperature drops to a low level. Plew and Pennak (1949) conducted year-long research on the vertical movement of zooplankton in Indiana Lake. Copepods (Cyclops bicuspidatus, Diaptomus birgeri and Naupleus larvae), a Cladocera (Daphnia longispina) and a Rotifer (Kellicitia longispina) observed vertical movement in all seasons. Their daily routine is much more in winter than in summer. The upward movement of Diaptomus birgei is slow in early autumn and the reverse is observed again in early spring.
Speed of Diurnal Movement: The speed of diurnal movement is determined by the variation of plankton, different environmental conditions and the age of the respective plankton. Plankton's speed of movement depends on (1) the approximate departure time from the lowest point and the time to reach the highest point, (2) the distance traveled, and (3) the rate of movement of different parts of the journey. Some plankton (Cladocera) move in a diagonal direction without going straight up in their daily movement. As a result, plankton travels a greater distance from the depth of water vertically. Different types of movement rates are taken from research articles which are given in the table below. In this case, the daily movement of some plankton in Lake Lawrence, Switzerland has been given speed.
Table: The speed of the zooplankton movement of the lake (From Worthington).
Range of Migration (meter)
Downhill speed (1 meter)
Rising speed (meter)
From noon to evening (1 m)
Next time from evening (1 m)
Daphnia longispina(Immature stage)
They do not go down
Bosmina coregoni(Immature stage)
Dont go upstairs
Diaptomus gracilis(Immature stage)
Diaptomus laciniatus(Immature stage)
Cyclops strenuus(Immature stage)
Effect of age on daytime movement: Some plankton offspring and mature phases vary in daily movement (Table). In the case of all plankton, there is no definite difference between the behavior of such daily movements. Such behavioral differences between adult and offspring are considered to be characteristic of a particular species. Such behavior may not apply to other species. Elsewhere in the daily movement, the effects of aging (e.g. in the larvae of Corethra) have been observed, but similar effects have been observed in plankton crustaceans.
Behavioral differences in daytime movement are observed between plankton of the same group in different reservoirs. For example, Malony and Tresler (1942) did not notice any specific daily movement in the Naupleus larvae of copepods in Caroga Lake, New York. Similarly, Pennak (Pennak, 1944) studied five lakes in the Colorado Mountains in late summer and did not notice the vertical movement of Naupleus larvae. However, according to Plew and Pennak (1949), Naupleus larvae's daily movement can be observed throughout the year on Lake Indiana.
Influence of Sex on Diurnal: Some plankton differ in daily movement depending on the sex. Such differences can be observed in both marine and freshwater. Some species of plankton are more active in special conditions. Pennak (1944), on the other hand, did not notice any gender differences in the daily movement of the Cladocera in some of the Colorado lakes.
Causes of Diurnal Mmovement of Zooplankton
The reason for the daytime movement of the zooplankton is somewhat known. Because the same species of zooplankton exhibits different types of behavior in different lakes, it is difficult to explain the reason for their movement. The main reasons for the movement of plankton are: light, temperature, food and relative density. Moreover, there are several other factors that influence the process.
Light: Light is thought to be an important factor in the daily movement of zooplankton. Little is known about how light affects the change in zooplankton density per second. In the evening, the zooplankton move to the upper level and as soon as the light rises in the morning they go down into the deep water. On cloudy days some crustaceans move closer to the surface of the water. At this time, like night, they can be seen in abundance in the upper level of water even during the day. On the other hand, they are not seen on the water level on a bright day. Other crustaceans are not sensitive to cloudiness and luminosity.
According to the latest data, each species has the highest tolerable light intensity. If possible, they move in that light. As the light decreases in the afternoon, the density of plankton on the surface of the water increases. As night approached, Plankton's upward movement ceased as the intensity of the light dropped below a tolerable.
The zooplankton spreads evenly everywhere in the desired location for its daily vertical spread. They are first seen on the surface of the water as the concentration of light is tolerable at the beginning of the day. The return to deep water then gradually decreases the density of the plankton. Worthington (1931) observed the following exceptions in his study of the vertical movement of macro plankton in freshwater in Lake Lawrence in Switzerland, Victoria and Niagara in Africa. According to him, the upward movement does not start before the daylight reaches its maximum level. For a few hours after the onset of twilight they show a tendency to random expansion over a very short range.
Plankton's daily movement occurs as water viscosity changes as a result of temperature changes during the day and night. However, this rule does not always apply. The idea is well established that temperature is not a direct or indirect factor in the daily movement of plankton. Studies at the field level and in the laboratory have shown that the thermal state of water affects the nature of the light response and that high temperatures increase negative phototropism. Low temperatures, on the other hand, reduce it.
Food: The relationship of food with daily movement is intimately involved. An abundance of phytoplankton is usually found near the surface of the water which is considered to be an excellent source of food for migratory plankton. Plankton move toward the surface of the water and toward areas near food outside of their territory. Although there is no food like the surface of the water, the daytime movement of plankton occurs in areas with severe food shortages due to gravity. It is thought (Dicse, 1914) that with the change in the intensity of light, different types of geotropism result in the daily movement of Daphnia pulex. In the case of some plankton, positive geotropism occurs when the intensity of light increases. On the other hand, when the intensity of light decreases, negative geotropism tends to occur.
Temperature affects geotopism: Low temperatures cause negative geotropism. Similar studies have been done on freshwater Cladocera.
Seasonal Distribution of Plankton
Qualitative relationship: Generally, natural water contains different types of plant and animal plankton or zooplacton. In addition to different types of plankton, different stages of their life-history remain in these waters throughout the year. Some plankton are seen at certain times of the year and not at other times. There are multiple reasons for Planckton's absence.
Total size of plankton: In all types of water bodies, the total size of plankton varies from season to season. The condition and amount of zooplankton do not vary in all types of water bodies. However, the total annual production of temperate lakes, especially first and second class lakes, produces a dual nature curve with two maximum yields (one summer and the other winter) (Fig.). This curve shows the highest yields in spring and autumn and the lowest yields in late summer and winter. Seasonal variations in different years may cause some variation in the maximum and minimum production period. Northern lakes in the United States have the highest spring yields and last from April to May. Rarely does it last until early June. The lowest production is here in summer.
This period lasts till August, with maximum production in autumn and minimum production in winter. This period lasts from February to March. There is no fixed rule for the relative size of maximum and minimum production. The maximum production in spring is higher than the maximum production in autumn. The minimum production in winter is usually lower than the minimum production in summer. Note that the same state of plankton production is observed in temperate seas. The maximum and minimum production of plankton varies greatly in different lakes and different environmental conditions.
Figure: Curve of dry organic matter of net plankton, nano plankton and total plankton of Mindota Lake (Wisconsin). Here A = total plankton; B = nano plankton and C = net plankton curve; The indicator numbers along the curve axis indicate the amount (milligrams) per cubic meter of water in the plankton.
Reasons for annual maximum and minimum production: There is a link between the maximum production in spring and winter and the change in the aquatic environment naturally. Plankton production is favorable at this time of the year due to the convection of previously stored nutrients in the bottom as a first class lake. As a result, plankton production increased quantitatively during this time. It should be noted, however, that even if a plankton species is at its maximum at any given time in an environment, it may not be applicable to other species.
These spring changing environments create favorable conditions for some plankton growth. Diatoms respond quickly to these new environments. As a result, diatoms predominate in the highest autumn production of spring plankton. Seasonal flooding occurs in shallow lakes, resulting in excessive release of essential elements such as nitrates, silica and other elements into the lake, resulting in excessive plankton production.
Other theories include temperature, light, dissolved oxygen, and a number of other environmental factors. According to one theory, phosphorus acts as a limiting factor. Adequate supply of nitrogen, potassium is required for phytoplankton. Phosphorus, nitrogen and potassium are readily available in natural water bodies on demand. However, since phosphorus is present in small quantities, it acts as a limiting factor for the growth of plankton algae.
Phytoplankton is found in the phosphorous region with a small amount of dissolved water in the surface. The growth of phytoplankton soon depletes the phosphorus. As phosphorus deficiency persists throughout the summer and winter, this condition persists until phosphorus is supplied again in spring and autumn.
Other conditions of plankton production: Sometimes there is no fixed period of plankton production in some water bodies. The highest and lowest production occurs spontaneously. Such irregularities are seen in both total plankton and individual production. This rhythm of maximum and lowest production results in excessive growth of some phytoplankton resulting in blooms. Such blooms are seen in summer as well as in winter. This type of bloom can occur in the same lake even in summer. Several species of bluish green algae such as Aphanizomenon flosaquae, Microcystis aeruginosa, Microcystis flosaquae, Gloeotrichia echinulata and some species of Anabaena create bloom. These algae are seen floating in large quantities in winter. Even at the top they make scum.
Seasonal history of plankton and Plankton species: Various studies have shown an abundance of diatoms in winter plankton. During this time bluish green algae (Myxophyceae) and green algae (Cholorophyceae) are largely absent. Bacteria and fungi do not show any specific seasonal abundance.
Pearsall (1932) studied the English lake and obtained the following information: (1) An abundance of diatoms is observed in winter and spring. During this time the water is rich in nitrate, phosphorus and silica. (2) An abundance of green algae and desmid is seen in summer. At this time the water contains low levels of nitrates and phosphates.
An important event in the biological history of plankton organisms is that the physical size of many plankton changes with the seasons. This phenomenon of plankton's physical shape or change in shape is called cyclomorphosis. In some cases, the summer and winter phases of the same species differ so much in shape that they are considered to be different species. However, such seasonal changes are not observed in all types of plankton. However, such phenomena can be observed in a significant number of plants and animals in the plankton world. The following fig. reflects the phenomenon of seasonal physical changes.
Physiological features of body shape change: All these seasonal changes in different plankton occur on such a large scale that it is considered a common occurrence. From winter to summer, the amount of body mass increases compared to the increase in body size. On the other hand, the opposite happens from summer to winter.
Figure: Line planets of some plankton's seasonal physical changes.
- The above row shows the change in the physical size of Daphnia cuculata with the change of seasons. The lower number indicates the date of acquisition of special physical constitution (the upper number indicates the name of the month and the lower number indicates the day.
- The middle row shows the seasonal variation of Bosmina coregoni. In summer, their bodies are taller than their height. However, in winter, the body is taller than the height. In summer the antennae are twice as long. The size of the eye is large in winter.
- The bottom row shows the seasonal variation of a rotifer (Aslanchna piodonta). The date is shown below. Three rows of animals have been placed in the same row for comparison.
Numerous such examples exist in natural water bodies are mentioned below:
General Biological Characteristics
Seasonal physical changes and some biological phenomena are mentioned below: Most of the following descriptions are based on a summary of Wesenberg Lund's (1926) findings.
Reasons for plankton's physical size change with the seasons:
(1) According to Wesenberg Lund (1900, 1926) the change in temperature causes the density to change which causes this phenomenon. At certain densities such physical changes occur in order to gain adaptation to a certain level of living. Plankton must sink and rise elsewhere as the density changes with the change of temperature over the seasons.
(2) In what ways do you have to qualify to float or swim? Due to this, the size of the body or swimming appendage will decrease or increase. As the temperature rises in the spring, the water density decreases and the plankton's immersion rate increases rapidly. To solve this problem, some plankton create summer phase. The amount of exposed surface increases relative to the body volume for adaptation to the new environment. Thus they achieve qualification to the new environment through adaptation.