Food Chain In Eagles Mere Lake
By Bill Feese
The food chain of Eagles Mere Lake begins with a group of free floating unicellular plants commonly known as algae, but known to aquatic biologists as phytoplankton (phyto; plant – planktos; drifter). Phytoplankton are the producers in the lake ecosystem. Through the chemical process of photosynthesis, these microscopic plants convert light energy into the chemical energy of food, which then becomes the source of food for all other organisms in the lake. While most algae exist as solitary single celled organisms (Fig. 1), there are many types in which their cells join together to form spherical or chain-like colonies (Fig. 2).
Desmids - Single celled free floating
Food produced by the phytoplankton begins to move through the food chain when these microscopic green plants are “grazed” upon by microscopic free floating animals known as zooplank- ton (zoo; animal – planktos; drifter). Zooplankton are the first order consumers in the lake. By feeding directly on the phy- toplankton, and then in turn being available themselves to be fed on by other larger consumers, zooplankton move food energy from the producer level of the food chain into the consumer levels of the food chain.
Most zooplankton are crustaceans, and are distant relatives of crayfish and shrimp. While they are described as microscopic, most are large enough to be just visible to the naked eye, and clearly visible to the numerous organisms that feed on them.
Figure 3 shows some of the more common zooplankton found in the lake. Many of these organisms have a small spot of pig- ment, incorrectly called the eye, which is light sensitive and en- ables them to stay in sun lit areas where the algae they feed on are found. In Cyclops, this “eye” is red and located in the center of the head. In the others, this spot is black. The Daphnia shown in the illustration had recently grazed and the intestinal tract is filled with algae and visible as a green tube running the length of the body. Cypris is shown grazing on a filament of Spirogyra. Gammarus is actually a type of freshwater shrimp.
Common Zooplankton organisms in EM Lake
The zooplankton are then fed on by organisms in the next level of the food chain known as second order consumers. In Eagles Mere lake this group is made up primarily of small fish and insect larva (Fig. 4).
Second Order Comsumers in EM Lake
Eagles Mere Lake is also home for one of the more unusual second order consumers, the freshwater jel- lyfish. These organisms use their ten- tacles to capture and devour large numbers of zooplankton (Fig. 5).
These secondary consumers
F i g . 5
then become available food for the members of the next level of the food chain, the third order consumers. This consumer level is usually composed of fish that feed primarily on insect larva and smaller fish. Figure 6 shows the primary third order con- sumers found in Eagles Mere Lake.
Blue Gill Sunfish
Third Order Comsumers in EM Lake
In EM Lake the fourth order consumer level consists of two species native to freshwater lakes, the Largemouth Bass and the Chain Pickerel (Fig 7). Fish in this consumer order are the larger fish species that feed primarily on other fish, but they will consume almost any other aquatic organism they are capable of swallowing.
Top Order Consumers in EM Lake
A food chain is not nearly as well defined as this description might suggest. In actuality a food chain is more like a food web, with organisms often moving from one consumer level to an- other as they mature, or as they vary their diet to take advantage of the availability of other food organisms, especially during times when their normal prey are scarce, or unavailable.