Elise Wach (Biology) University of Southern California
A recent study indicated that several species of fish, namely Clinostomus funduloides, enter the streams around Lake Matoaka when detention ponds overflow during storm events. The purpose of this study was to determine whether these fish have a top-down control of stream ecosystems.
A controlled laboratory study showed that the fish prey upon the amphipod Gammarus pseudolimnaeus with a strong preference for smaller sized individuals. The relationship between amphipod populations and leaf litter decomposition was then analyzed in Strawberry, Berkeley and Pogonia Creeks. Leaf litter bags were placed in areas with and without fish in each stream. After a five week period, the number of amphipods was significantly lower in the sites where fish were abundant. Moreover, the average size of the amphipods in the areas containing fish was larger, indicating that the presence of fish does, in fact, influence the amphipod community structure.
Gammarus pseudolimnaeus is a shredder, essential in the decomposition of leaves. Therefore, the decomposition rate of the leaf litter was expected to be lower in the areas populated with fish. However, no significant difference in the breakdown rate was found between areas with and without fish. Potential explanations for these results include possible leakages, differences in turbidity, dissolved oxygen and the availability of other food sources. Future studies must be conducted to determine the direct correlation between the abundance and size of amphipods and leaf litter decomposition
For additional documentation Elise Wach provided a PowerPoint Presentation entitled "Fish, Amphipods and Leaves: How are they related?" provided here in PDF form.