Essay On Daphnia Magna

The purpose of this study is to understand the feeding rate of Daphnia magna. D. magna is a species of Daphnia that belongs to the suborder Cladocera (Ebert, 2005). They live in freshwater and feed on small, suspended particles in the water. They are filter feeders. Phyllopods, which are leaf-like appendages, provide a filtering apparatus for the collection of food. These structures beat to produce a constant current of water, allowing particles to be filtered by fine setae on the thoracic legs. The particles are then transferred to their mouth groove to be ingested. D. magna typically feed on planktonic algae (Ebert, 2005). The following experiment uses algae to test what affects the feeding rate of D. magna. The rate of filtration is dependent on multiple factors including temperature, food density, body size, and water pH.
As expected, the control group had a feeding rate between that of the higher and lower light intensities. Buikema (1973) mentions that light intensities that exceed a certain threshold tend to suppress the filtering rate. We theorized that their feeding rate increased in the dark environment because it reflects their natural habitat. Populations of D. magna perform diel vertical migration, which means that they only spend the night in surface layers of the water and migrate downwards into the lower water layers during the day (Dodson, 1990; Haney, 1985). The ultimate cause for this is to protect themselves from predators. The proximal cause is the change in light intensity. D. magna present with photosensitive behaviour and they tend to move into areas of low light (Dodson, 1990). Young et al. (1984) report a decrease in the rate of limb beating when exposed to increased light intensity. The rate of limb beating directly affects the rate of filtration. If there is a decrease in the rate of limb beating then the feeding rate will also