The Daphnia have leaf-like appendages used in respiration, filter feeding and locomotion (Miller, 2010). Unfortunately, due to the size of these crustaceans they are often easy prey for bigger organisms in their ecosystem. Daphnia are often found in the bottom layers of the water column during the day and the upper layer at night to avoid visually feeding fish (Disavowing, 1992). Daphnia can be found in estuaries where there are various levels of salinity in the water.
Estuaries are partially enclosed coastal bodies of water that have an opening to the ocean (Columbia University Press, 2011). This opening causes freshwater from inland and saltwater from the ocean to mix, determining the populations and numbers of these daphnia in different areas of the estuary. Estuaries represent one of the most ecologically important habitats on earth because they serve as sanctuaries for a variety of vulnerable organisms. However, human impacts on these estuaries are having a negative effect on the life of organisms that have made these their home.
One example is that the withdrawal of freshwater is increasing the levels of salinity into the estuaries making it uninhabitable for daphnia among other organisms (Columbia University Press, 2011). In the experiment conducted on the daphnia, the goal was to determine the effects that the salinity of the water had on the survival of the daphnia, by introducing them to different levels of saltwater and observing the actions of these crustaceans and how they tolerated the various levels of saltwater.
The proposed hypothesis was that high concentrations of seawater had a negative effect on the survival of the daphnia. Since the daphnia live in estuaries where the boundary between fresh and seawater is ever changing, we expect to see that the daphnia have a tolerance to saltwater but may not survive in parts of the estuary where there re higher concentrations of it. A higher percentage of daphnia is expected in areas where seawater is minimal.