Daphnia and The Effect of Salinity and Temperature

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The environmental factors of importance for Daphnia Magna's behaviors

The environmental factors of importance for Daphnia Magna's behaviors are salinity and temperature. Salinity is the concentration of dissolved salts in a given amount of water (Arnér & Koivisto, 1993). The salinity of water sources is caused by intensified weathering cycles that wash minerals down river drains, which ultimately flow into bodies of water such as lakes and oceans. The liquids evaporate as a result of evaporation, leaving the rocks and salts behind (Calaban, & Makarewicz, 1982; Heugens, et al., 2003). Higher temperatures increase the rates of evaporation, causing water body salinity to rise as temperatures rise. On the other hand, higher temperatures emanating from the changes in rain and snow patterns, the rise in sea level, more droughts, warmer oceans and increased ocean salinity (Ashforth, & Yan, 2008). In general, the major cause of climatic change leading to salinity and temperature variations is the global warming, which is a major cause of climatic changes dependent on both natural phenomena and anthropogenic activities.

Daphnia Magna

Daphnia magna is mainly a freshwater crustacean. On the other hand, the species live in other aquatic environments including acidic swamps, ponds, streams, and rivers. It is the largest of the Daphnia species. Daphnia magna according to Chen, & Stillman (2012) is suspension feeders who gather their food through filtering apparatus the phylopods. They can also feed through clinging to plants and other substrates where they browse over the surface and pick the smaller particles they can find (Blaise, & Férard, 2005). They reproduce through asexual mode. Their photo tactic behavior such that with positive genotypes tend to spend most of their time in the upper water level and vice versa (Ghazy, Habashy, Kossa, & Mohammady, 2009; Gonçalves, Castro, Pardal, & Gonçalves, 2007). Daphnia magna species compared to other Daphnia species is preferred for this project due to their ability to be more sensitive to environmental factors as contaminants compared to other alternative invertebrate species.

Justification for Examining Differential Response to Environmental Factor

The reason for examining the differential responses to environmental factors includes the need to determine whether it is only predation by the fishes and size-dependent competition, which controls the population of the Daphnia magna species (Kim, Park, Kim, Lee, Choi, & Choi, 2010). In this view, salinity and temperature are debated to be other contributory factors to managing the population of Daphnia magna. Varying salinity and temperature leads to variation in water quality which relative affects the survival rates of Daphnia magna. For instance, in a period of about 48 hours to 98 hours, the median lethal concentrations has no effect on the lives of the Daphnia magna species until after 98 hours when the populations are observed to vary by reducing. The recommended salinity should be below 5% while others tolerate salinity of up to 20% (Smirnov, 2014).


Importance of the Interaction

The interaction of the Daphnia magna species with the environment is significant for purposes of understanding and determining the effects of salinity and temperature on their survival, growth, and reproduction efficacies (Hall, & Burns, 2002). Notable is the fact that salinity and temperature vary during the various seasons. Thus, each season presents varying challenges and threats in regards to the survival of the Daphnia magna species. For instance, during the summer season, temperatures are very high leading to increased rates of evaporation translating into increased salinity of the water bodies. The fluctuation in water salinity relatively affects the Daphnia magna population dependent on the survival of mature species as well, egg production. Due to fluctuations in salinity and temperature, the environments change, thus, Daphnia magna species need to devise varying adaptation measures suitable for their homeostasis balance.

Ecological Significance

The Daphnia magna species have a very significant role as far as the ecology is concerned. The fact that they inhabit many water bodies worldwide exemplifies them as major components of the food web or food chain that is dynamic. The species is a strong and significance ecological interacts due to their characteristic of being both primary consumers of the phytoplankton as well as a secondary food source for the secondary consumers in the food web. According to (Hall, & Burns, 2002), the species, furthermore, occupy a very a very unique position in the pelagic ecosystem due to their ability to graze on the phytoplankton as well as cycling nutrients not limited to the fact that they are valuable prey for many secondary consumers. Above all, the Daphnia magna species have an influence on the strength of interactions due to their property of being genetically variable, which guarantees their population a range of morphological adaptations, physiological as well as behavioral adaptations necessary for survival (Heugens, 2003).

Expected Results

Increased salinity and high temperatures are expected to cause a reduction or at least disappearances in the number of Daphnia magna species in the aquatic environment under investigation (Gonçalves, Castro, Pardal, & Gonçalves, 2007). At salinity range of between 20-3000mg-Cl and temperature range of between 10-20oC. Adults or mature Daphnia magna species are expected to survive maybe 48 hours more at salinities of concentration less or equal to 1000mg-1Cl. In particular, survival is expected to be high at a temperature of 10oC compared to survival rates at 200C where the disappearance of the species is common. Nonetheless, females are expected to show higher survival estimated at 86% at 100C and 14% at 200C (Lampert, & Sommer, 2007). Similarly, survival of male Daphnia magna species 43% at 100C and 0% at 200C. The revelation is that females have a higher tolerance to salinity and higher temperatures compared to males. Egg production is generally expected to decrease with increase in temperature for example in successive egg production, at 100C is expected to be at 20 for the twenty days of the experiment and 15 at 200C (Lampert, & Sommer, 2007).

The expected results depict the real life scenario in the ecological system where mortality rate of magna increases significantly during the summer seasons where there is relatively increase in salinity in the water bodies caused by increased evaporation rates as well as increased temperatures (Lampert, & Sommer, 2007). The increase in mortality rate leads to imbalance in the aquatic ecosystem by disrupting the food chain in which fishes that prey on the magna species also decrease in number.


Qualitative expectations, on the other hand, regard the concentration of the saline environments. For instance, qualitative aspects pay attention to certain aspects including the lethal dose concentrations and the median concentrations (Teschner, 1995). The other simpler qualitative aspects of the experiment would be to investigate the effect of the acceptable salinity, which determines the survival and tolerance capacity of Daphnia magna to harsh environment.

The implications are that at higher salinity Daphnia species are expected to have lesser survival chances. In correspondence, females are nevertheless, expected to be highly tolerant to the extra saline.


Arnér, M., & Koivisto, S. (1993). Effects of salinity on metabolism and life history characteristics of Daphnia magna. Hydrobiologia, 259(2), 69-77.

Ashforth, D., & Yan, N. D. (2008). The interactive effects of calcium concentration and temperature on the survival and reproduction of Daphnia pulex at high and low food concentrations. Limnology and Oceanography, 53(2), 420.

Blaise, C., & Férard, J.-F. (2005). Small-scale freshwater toxicity investigations. Dordrecht: Springer.

Calaban, M. J., &Makarewicz, J. C. (1982). The effect of temperature and density on the amplitude of vertical migration of Daphnia magna. Limnology and Oceanography, 27(2), 262-271.

Chen, X., & Stillman, J. H. (2012). Multigenerational analysis of temperature and salinity variability affects on metabolic rate, generation time, and acute thermal and salinity tolerance in Daphnia pulex. Journal of Thermal Biology, 37(3), 185-194.

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Gonçalves, A. M. M., Castro, B. B., Pardal, M. A., &Gonçalves, F. (2007). Salinity effects on survival and life history of two freshwater cladocerans (Daphnia magna and Daphnia longispina). In Annales De Limnologie-International Journal of Limnology (Vol. 43, No. 1, pp. 13-20). EDP Sciences.

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Heugens, E. H., Jager, T., Creyghton, R., Kraak, M. H., Hendriks, A. J., Van Straalen, N. M., &Admiraal, W. (2003). Temperature-dependent effects of cadmium on Daphnia magna: accumulation versus sensitivity. Environmental science & technology, 37(10), 2145-2151.

Kim, J., Park, J., Kim, P. G., Lee, C., Choi, K., & Choi, K. (2010). Implication of global environmental changes on chemical toxicity-effect of water temperature, pH, and ultraviolet B irradiation on acute toxicity of several pharmaceuticals in Daphnia magna. Ecotoxicology, 19(4), 662-669.

Smirnov, N. N. (2014). Physiology of the Cladocera. London: Academic Press.

Teschner, M. (1995). Effects of salinity on the life history and fitness of Daphnia magna: variability within and between populations. In Cladocera as Model Organisms in Biology (pp. 33-41). Springer Netherlands.

Lampert, W., & Sommer, U. (2007). Limnoecology. Oxford: Oxford University Press Inc.

January 05, 2023



Chemistry Nature Biology

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Salt Water Plant

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