Amphipods play important roles in the cycling of nutrients and energy in many aquatic systems where they display a wide range of feeding modes ranging from detritivore to predator. Although the biology of many amphipod species has been examined, little is known of hypogean amphipods inhabiting cave streams. Gammarus troglophilus is a stygophilic amphipod that co-occurs with the federally endangered stygobiont G. acherondytes in cave streams of the Salem Plateau Karst Region of southwestern Illinois. With the goal to establish a self-sustaining laboratory population of cave amphipods to obtain amphipods for lethality experiments, we tested hypotheses relating the survival and growth rates of G. troglophilus collected from cave streams to different laboratory conditions of food and water velocity. We used a series of microcosm experiments to test the hypotheses that survival and growth are not affected by type of water (cave water vs. amended water), water velocity (static vs. dynamic/recirculating), or the type of available food (sediment vs. sediment, leaf discs, and TetraMin®). We also tested if different food treatments affected the survival and/or growth of juvenile amphipods and newly released neonates in static chambers. Our results indicate that cave water was important for survival because no amphipods survived past 30 days in experiments with water amended to resemble cave water. The addition of food (leaf discs and TetraMin®) and water velocity affected survival but not growth rates in microcosm experiments. Food treatment (leaf discs vs. TetraMin®) did not significantly affect survival or growth rates of juvenile amphipods. However, leaf discs increased the survival and growth of neonate amphipods. Overall, survival was low in all experiments and further research is needed to examine the effects of handling stress on survival during experiments because amphipods left in stock tanks survived and grew well.
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Vol. 31 • No. 3