Colonization and Persistence of the Freshwater Amphipod, Crangonyx pseudogracilis, in Temporary Ponds: Aspects of its Ecology, Resistance to Desiccation, and Dispersal Abilities

Abstract

Crangonyctid amphipods occupy temporary habitats throughout northeastern North America but they are mostly known as permanent water species. Crangonyx pseudogracilis is found at high densities in temporary ponds in western New York but the means by which it colonizes and persists in temporary ponds were not well understood before my study. My objectives were to 1) learn more about and quantify the colonization abilities of C. pseudogracilis by performing experiments where holes were dug around temporary ponds; 2) explore the ability of the amphipods and other invertebrates to descend through inundated porous substrates in the laboratory; 3) compare the lifecycles of permanent and temporary populations and how the timing of mating and releasing of broods may be related to survival through the dry season; and 4) understand how and where the amphipods find refuge when a pond dries. During periods of inundation, C. pseudo gracilis was found in the top 15 cm of soil below and at the edges of the pond basin. After the pond basin became dry, they probably descended in the soil to depths greater than 45 cm. C. pseudogracilis and planarian flatworms readily colonized holes dug on the perimeter of the pond. In the lab, amphipods, flatworms, and ostracods readily descended through porous substrates. C. pseudogracilis has an annual lifecycle; the previous year's generation began dying in May and was gone by the end June. Ovigerous females were found from 23 March until 28 May. In the laboratory, amphipods survived in soil with an average moisture content of 51 % for 15 weeks. My results suggest further studies. 1) Populations of C. pseudo gracilis in permanent waters migrate to deep water during the same time of year as the temporary ponds I studied dried up. Whether amphipods in permanent waters burrow into bottom sediments during the dry season should be studied. 2) Determine how deep amphipods descend into pond sediments of temporary waters during the dry season. 3) Examine in detail the importance of the soil/water ecotone for organisms living in temporary waters.