Impact of Abiotic Stress on Phytoplankton and Zooplankton with Special Reference to Food Web

Abstract

In aquatic ecosystems, bacterial colonies constitute an important aspect of biological diversity and biogeochemical cycling. Phytoplankton is the primary producer of the food web and zooplanktons are an important part of freshwater food webs and biogeochemical cycles, as they serve as the main trophic connection between primary producers (phytoplankton) and fish. This chapter conducts abiotic stress effects on phytoplankton and zooplankton along with the impact of abiotic stress on their energy succession. Abiotic stress shows the decreasing supply of essential vitamins due to abiotic stress can have huge consequences for the aquatic food web. Abiotic factors had a significant impact on the biomass of phytoplankton and zooplankton communities exposed including increased temperature, acidification, nutrient enrichment and increasing ultraviolet (UV) environment of the aquatic ecosystem that significantly affect their survival, behaviour, nutritional procurement, reproduction and their overall population dynamic. Oxygen stress also is a widespread occurrence in freshwater environments, with the depletion of DO in the water layers under the epilimnion becoming increasingly common. At moderately high salinities, a decreased top-down control by zooplankton on phytoplankton may be an indirect result, leading to a worsening of eutrophication symptoms.

1. Introduction

In aquatic ecosystems, planktons form the base of the food web. Planktons are microscopic organisms that flow with streamlined water. The term “Plankton” is used to describe all non-motile, water-current-resistant organisms that are present in both freshwater and marine environments. Water current carries them along. Its range in size is from 0.2 mm to more than 20 cm ranging from tiny microorganisms to enormous creatures like jellyfish. Their distribution changes depending on the amount of light and nutrients available. Planktons are a source of food for large aquatic species. It shows the dynamic nature of the aquatic ecosystem due to which they act as the most dominating group among all water bodies. Planktons survival depends upon the structure of the aquatic ecosystem and the availability of nutrients. They adapt themselves into strategic adaptations. Planktons are acts as an important biological indicator of water quality and also determine the trophic status of an aquatic ecosystem. They are categorised into Phytoplankton and Zooplankton.

Phytoplankton also known as microalgae are chlorophyll-containing organisms that require sunlight to grow and survive. The majority of phytoplankton remains buoyant and floats in the upper layers of the ocean where sunlight can reach them. Additionally, phytoplankton needs inorganic elements like nitrates, phosphates and Sulphur which are essential for making proteins, lipids and carbohydrates. The phytoplankton plays important role in the production of oxygen by the process of photosynthesis in the presence of light, e.g. during the daytime, the water column forms the photic layer. Firstly, oxygen enters in water and then evaporates into the air from the water surface thus; it is contributing oxygen to the atmosphere. A decrease in the oxygen productivity by phytoplankton can disturb the balance between earth and life which further cause extinction in organisms. The phytoplankton forms the base of the food chain in an aquatic ecosystem. They also convert solar energy into chemical energy thus, they act as energy transducers. This converted energy is transferred by zooplankton to the higher trophic levels while providing the link between producers and consumers. The growth and morphological properties of phytoplankton are examined by the assessments of biological and physico-chemical parameters of an aquatic ecosystem.

Zooplankton is microscopic organisms that are present in the water column of almost all water bodies, such as lakes, ponds, and seas. However, they are largely unable to survive in rivers and streams. They may contain the larval stages of larger organisms like mussels and fish and range in size from a few millimetres to a few microns (1 μm is equal to 1/1000 of a mm).

Zooplanktons are microscopic organisms that are present in the water column of almost all water bodies, such as lakes, ponds and seas. However, they are unable to survive in rivers and streams. They may contain the larval stages of larger organisms like mussels and fish which range in size from a few millimetres to a few microns (1 μm = 1/1000 of mm). They also act as a food source for invertebrates and fishes. They play important role in the transmission of energy to higher trophic levels. The seasonal variations in an aquatic ecosystem can cause fluctuation in environmental characteristics to result from abiotic stress. This abiotic stress causes a greater impact on patterns of energy succession.

In an aquatic ecosystem, extrinsic and intrinsic interaction is observed. The intrinsic interaction is defined as competition, parasitism, predation and mutualism and the extrinsic is known as an interaction between aquatic organisms and their environment. They both cause an impact on the dynamic pattern of taxa because seasonal variations could vary the communities. The energy flow of the biotic factors ecosystem starts with photosynthetic organisms which use solar energy to convert inorganic compounds to organic compounds. The diatoms and dinoflagellates are more dominant species in the marine ecosystem, which are primary producers in the classical food web. The primary predators are Zooplankton for phytoplankton which is get affected by variations in environmental factors [1, 2, 3, 4, 5, 6, 7].

In this chapter, the impact of abiotic stress on phytoplankton and zooplankton energy succession has been discussed. Analysis, the regulation of zooplankton can be examined by phytoplankton composition [8]. In Mesotrophic Lake, Predation can cause the breakdown of blooms of bacteria-plankton and also varies the phytoplankton structure [9]. The interaction between phytoplankton and zooplankton is depending upon the trophic status of an aquatic ecosystem [10, 11] (Figure 1).

Figure 1.

Abiotic stress impact on food web.

2. Abiotic stress impacts α-tocopherol and β-tocopherol antioxidants

In aquatic ecosystems, the phytoplankton is a major source of non-enzymatic antioxidants and their precursors for primary consumers and other organisms higher up in the food web [12, 13, 14]. Antioxidants can be categorised into two categories: (1) enzymatic antioxidants such as superoxide and (2) non-enzymatic antioxidants such as glutathione, α-tocopherol (vitamin- E) and β- carotene. In an aquatic ecosystem, the phytoplankton the antioxidants α-tocopherol (vitamin E) and β-carotene in phytoplankton depend on changes in abiotic factors.

The α-tocopherol plays important role in the protection and prevention of membrane lipids whereas β-carotene act as antennae of complex photosystem II. The maximum variations in antioxidants in the aquatic ecosystem are because of temperature, density and salinity fluctuations. The antioxidant value in phytoplankton directly depends upon the composition of species, physiological characteristics and their strategies to deal with oxygen species. The α-tocopherol and β-tocopherol are non-enzymatic antioxidants which are produced by photosynthetic organisms at higher trophic levels in the form of dietary intake due to system shifts toward the phytoplankton can cause environmental variations which cause a larger impact on aquatic food webs. The composition of species decreased due to unbalancing of tocopherols.

3. Impact on vitamin B1 (thiamine)

Vitamins play important roles for plants and animals. Thiamine (vitamin B1) compound is soluble in water. The structure of pyrophosphate is consisting of pyrophosphate ester and thiamine diphosphate (TDP) which act as a cofactor in many reactions of metabolic. It also plays role in acetyl-coenzyme A and it also has a role in the Kerb cycle. Thiamine monophosphate (TMP) is intermediate in thiamine metabolism. The ethology of thiamine deficiencies is not well known but some researchers illustrate that transmission of thiamine gets decreases from phytoplankton to other higher trophic levels in an aquatic ecosystem. This result that variation in thiamine causing an impact on the composition of species with lower thiamine content and also decreasing the thiamine cellular concentration. In a marine food web, the synthesis of thiamine is done by prokaryotes and phytoplankton which are further transmitted to higher trophic levels through energy succession. But only some species of phytoplankton can secrete thiamine but not all species synthesise thiamine. It has been observed that both thiamine autotrophs and thiamine producers can uptake external thiamine.

The salinity in the water caused a larger impact which was further followed by temperature and photon flux density were examined in phytoplankton species. This effect can cause a decrease in thiamine concentration availability for the aquatic food chain and food webs. The decrease in thiamine concentration shows a larger impact on the aquatic food webs. It is an unclear statement that vitamin variations are more efficient to cause an impact on grazers in climatic conditions. The mechanism for example selective grazing in zooplanktons also causes an impact on their nutritional habits. Vitamin B1 in diatoms increases at high temperature whereas it lowers at salinity.

The decreasing fatty acid level shows an adverse impact on growth and also affects the transmission of carbon in the food web [7, 15, 16]. The zooplankton fatty acid depends upon the fatty acid of phytoplankton and their composition but zooplankton causes greater inter-specific differences [15, 17]. The thiamin content of copepod is closely related to the thiamin concentration of micro, nano and pico- plankton while there is some difference in thiamine content of copepod species. Hence, aquatic food web processes depend upon the concentration of thiamin at the higher trophic level.

4. Eutrophication

The assessment of physico-chemical parameters is necessary for examining the water quality and energy succession of an aquatic ecosystem. The abundance and diversity of phytoplankton and zooplankton depend upon the physico-chemical parameter of an aquatic ecosystem [18]. Eutrophication is defined as the process by which all nutrients are accumulated in all aquatic ecosystems. Eutrophication is a major problem for the aquatic food web. This is caused by the increase in the concentration of phosphorus and nitrate. The formation of algal blooms limits the intake of oxygen for phytoplankton and another organism which can cause the death of an organism. The water of algal bloom smells foul and it also causes the death of fish. The negative effects of eutrophication on water bodies include a decrease in biodiversity can also toxicity in water bodies and a change in species abundance (Figure 2).

Figure 2.

Eutrophication process.

4.1 Classification of eutrophication

4.1.1 Anthropogenic eutrophication

Anthropogenic eutrophication is occurring through human activity such as golf courses, lawns etc. in the form of fertilisers which get a transfer into water bodies. When it comes in contact with algae and plankton it causes eutrophication. The variation of nutrient which enters water bodies by human intervention increase eutrophication rapidly. This eutrophication process does not require decades. Cultural eutrophication begins with phosphorus which is present in fertilisers along with partially sewage treatment. Phosphorus is considered the strongest indicator of the growth of algae. Deforestation and soil erosion are the major cause of eutrophication.

4.1.2 Natural eutrophication

Natural eutrophication is defined as the enrichment of water bodies with help of natural calamities. This process takes a slow time as compared to anthropogenic eutrophication. It depends upon the environmental temperature. Natural eutrophication duration is up to 100 years because in this process organic matter takes a long time for the deposition. Natural eutrophication occurs in natural conditions like landslides and floods with environmental characteristics such as temperature, carbon dioxide and light also play important role in natural eutrophication. The natural eutrophication primary stage starts in oligotrophic water in which accumulation of nutrient take place. The accumulation of nutrients and their utilisation get continues which further causes eutrophication. The duration of eutrophication depends upon the variation of water quality (Figure 3).

Figure 3.

Types of eutrophication and their causes.

4.1.3 Effects of eutrophication

During eutrophication, phytoplankton grows faster. These phytoplankton species are toxic. In eutrophic water, the gelatinous zooplankton bloom grows faster in this water. Biomass of algae increases in eutrophic water. The loss of transparency in water and water smell and colour. The shellfish and harvestable fish population get decreased. The concentration of dissolved oxygen decreases which causes the death of fish.

5. Ocean acidification

Ocean acidification is a steady decrease of the pH concentrations as a result of the release of carbon dioxide (CO₂) from the atmosphere. Human use of fossil fuels is the barrier to ocean acidification. The CO₂ concentration is obtained from the atmosphere which depends upon the interactions between biological activities and physico chemical parameters such as temperature, salinity, intensity and surface chemistry. The decrease in the pH concentration because of anthropogenic CO₂ concentration causes ocean acidification [19, 20]. Ocean acidification is controversial that how it causes an impact on the carbon fixation by photosynthetic organism. The process of calcification in phytoplankton gets affected by the influence of ocean acidification. Ocean acidification caused due to global warming as well as it causes environmental factors on productivity and composition. Ocean acidification serious problem which affects the growth and development along with the nutritional quality of primary producers which further affects the higher trophic levels. The phytoplankton biochemical composition gets disturbed during acidification causing an impact on the taxonomic group. The sensitivity to pCO2 causes low food quality for higher trophic levels. Zooplankton is less affected by acidification but the acclimation process leads to an increase in the rate of respiration and also an increase in the rate of grazing. Because their shell is mainly composed of chitin which prevents them from acidification. At higher trophic levels organisms are more affected because the outer skeleton is made up of calcium carbonate.

6. UV radiation

During summer, growth and development decrease growth of phytoplankton when UV radiation are high this shows that phytoplankton species show complexity toward UV radiation and temperature. Moreover, they are dependent on UV radiation and temperature [21, 22, 23]. UV radiation also affects the growth and development of zooplankton and also changes their pattern of species composition. The cell size variation due to UV radiation causes an impact on zooplankton feeding habits. The phytoplankton gets more affected by high UV radiation compare to zooplankton. UV Radiation causes a moulting process for a few zooplankton present in the water bodies. The process of Moulting involves chitinolytic enzyme and apoptosis process done by caspase-3-activity. It has been observed that UV radiation cause an adverse impact on the moulting process as a result it decreases the growth and development of the population dynamic of plankton. The UV-B radiation can strongly cause impairment of photosynthesis whereas inhibition of calcification is done by UV-A radiation. The outer calcified scales form an exoskeleton. At maximum calcium concentration, the zooplankton more resists UV radiation rather than at limited calcium concentration (Figure 4).

Figure 4.

Factors affecting the phytoplankton and zooplankton.

7. Conclusion

This chapter suggests a well understanding of phytoplankton and zooplankton along with their role in the ecological succession and food web. The seasonal changes show an impact on the physicochemical parameters which changes the patterns of the composition of species. Mostly they depend upon the Temperature. These factors affect the growth and development of higher trophic levels in the food web The abiotic stress such as antioxidants, vitamins, eutrophication, acidification and UV radiation show an impact on phytoplankton and zooplankton. Antioxidants such α-tocopherol and β-tocopherol secretion in the phytoplankton depend upon the seasonal variations. The unbalancing in the α-tocopherol and β-tocopherol also disturbed the composition of species. The thiamine deficiency decreases the growth and development at a higher trophic level. The ethology of thiamine deficiencies is not well known but some researchers illustrate that transmission of thiamine gets decreases from phytoplankton to other higher trophic levels in an aquatic ecosystem. This result that variation in thiamine and also causes an impact on the composition of species with lower thiamine content and decreases the thiamine cellular concentration. Eutrophication is a major problem for the aquatic food web. This is caused by the increase in the concentration of phosphorus and nitrate the negative effects of eutrophication on water bodies include a decrease in biodiversity can also toxicity in water bodies and a change in species abundance. However, acidification affects phytoplankton biochemical composition which gets disturbed during acidification causing an impact on the taxonomic group and UV radiation shows an adverse impact on the phytoplankton which further limits the all type of nutrition for higher trophic levels. These abiotic stress show harmful effects on the food web and the composition of species.