Investigate the feeding relationship of invertebrates in ponds of different light levels.

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Aim: 

To investigate the feeding relationship of invertebrates in ponds of different light levels.

Background Research:


A two-flapped shell that creates an opening on the underside covers the water fleas body. The two quite complex eyes have grown together. The second pair of antennae is large and is used to swim. The head is large, and the rostrum is pointed and powerful. There is also a point on the shells upper side.  They are 6mm in length.

 
Water fleas are mainly freshwater organisms, but a few species tolerate
. Because of this they are found in  and in relatively closed seas with a large run-off of freshwater. They are normally found only as deep as a few meters in the water. 

Water fleas eat plants and other particles in the water. Therefore they are herbivores (primary consumer). Larger creatures, for example, phantom midge larvae (Carnivores) feed off water fleas. With some females the young water fleas developed in the ovary without being fertilized. Several generations with only females can occur and multiply themselves partenogenetically. When harsher conditions prevail even males and certain females whose eggs were fertilized hatch. The ovaries are released when sloughing takes place or when there is a drought and are spread over large areas by the wind. Water fleas exist globally.


An ecosystem is defined as 'a self-contained interacting community of organisms, considered with the environment in which these organisms live and react'. Freshwater ecosystems include such water bodies as lakes, rivers, ponds and streams. They do not include saltwater bodies such as oceans or seas. A pollutant may be considered as any substance or form of energy, usually an unwanted by-product or waste, which is released into the environment as a result of human activities, that alters the chemical, physical and biological characteristics of the environment. Such substances may be solids, liquids or gases. Freshwater ecosystems can become affected in a number of ways, such as by , , and .

As the water becomes more polluted, there are more organic nutrients available for the bacteria to break down which leads to an increase in mineral salts.  This is known as eutrophication ("good eating" conditions). However, the breakdown of these nutrients leads to depletion in oxygen and an increase in CO2, which can lead to the death of many of the other organisms such as fish and invertebrates, which depend on the ecosystem remaining balanced. Eutrophication encourages the growth of algal blooms, which cover the surface and prevent light from reaching the submerged plants in the water thus preventing photosynthesis. The problem is greatly enhanced at nighttime, when plants have been unable to produce sufficient levels of oxygen for the invertebrates to respire. Eutrophication has the following effects on the ecosystem:

  1. Affects animals and invertebrates, by causing lower oxygen levels, too low for animals to respire effectively
  2. Increases turbidity / cloudiness, reducing light levels and thus reducing photosynthesis by plants 

This would have a great effect on the freshwater pond, as if there is no light the plants would be able to photosynthesise and would die, resulting in the death of invertebrates as they would have no food to eat, and would probably have a great effect on the freshwater pond food web.

A similar investigation that was carried out by Marianne V. Moore and Susan J. Kohler of Wellesley (Mass.) College had examined how artificial light affects small aquatic invertebrates in New England freshwater ponds. Their data shows that the night time activity of these animals near the surface drops off in proportion to the amount of light reaching them. That could reduce the invertebrates' predation on algae at the surface, potentially leading to algal blooms and poor water quality.

The experiment shall take place in two different ponds, woodland pond and a meadow pond. As the woodland pond has trees surrounding it, the light intensity is a lot less in comparison to the meadow pond where there is no obstruction to light.

Apparatus

Fishing Net – To capture the organisms from the freshwater pond. The fishing net is classed as a ‘small’ one and has very small fine holes in the net.  

Standard Tray – The tray is 30 x 20cm is size and it is going to be used for      emptying the contents of the net into it for inspection.

Light meter  - To measure the amount of light available to the ponds. There are three different light scales. X10, x100 and x1000, in order to get a high degree of accuracy from our results we shall be measuring light in x1000 mode.

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Glass beaker – to measure oxygen-testing liquids.

Goggles – eye protection so that nothing can get into our eyes while we are doing the experiment and wont catch any disease.

Oxygen Kit – This is a kit that is used to measure the amount of oxygen that t   there is in the freshwater pond. It contains instructions and 6 reagent bottles.

Spoon – to stir the captured sample and take out pond plants.  

Square container – used to enclose the organisms in a small region of the tray.

Pencil/paper – To use to write ...

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