Colonization and persistence of Crangonyx pseudogracilis (Bousfield 1958) in temporary pools

Abstract

Crangonyctid amphipods occupy temporary habitats across northeastern North America, but they are mostly known as permanent-water species. Crangonyx pseudogracilis (Bousfield 1958) is found at high densities in temporary pools in western New York, but the means by which it persists are not well understood. Our objectives were to: 1) assess the dispersal abilities of C. pseudogracilis, 2) explore its ability to descend through inundated porous substrates, 3) assess whether its life cycle and brood releases are related to survival through the dry season, and 4) find their dry-season refugia and measure the period for which they can survive desiccation. During periods of inundation, C. pseudogracilis was found in the top 15 cm of soil in holes <10 m from pools. After pools dried in mid-June or early July, C. pseudogracilis was not found in the soil to a depth of 45 cm, even when rains temporarily refilled the pools. In the laboratory, small C. pseudogracilis descended easily through substrates with ? 0.7-mm pore radii but large (? 7 mm) and ovigerous C. pseudogracilis were unable to descend. In the field, ovigerous females were found from mid-March until late May. The previous year’s generation of large and ovigerous individuals began dying in May and was gone by the end June. In the laboratory, C. pseudogracilis survived in damp soil (51% average free moisture content) for 15 wk. Crangonyx pseudogracilis lacks specialized strategies for survival in temporary waters (e.g., resting eggs, dormant juvenile stages, active burrowing), but has ecological traits well suited for temporary pools and similar environments