Distribution, abundance, and vertical migrations of Leptodora kindtii in a mainstem Missouri River reservoir, Montana, USA

摘要

Leptodora kindtii , a large, mobile, predaceous cladoceran zooplankter has been shown to make diel vertical migrations in some localities. L. kindtii were sampled in summer in the headwaters of Fort Peck Reservoir, Montana, USA, to assess and compare their dayight abundance in three habitat types (riverine, transitional, and reservoir), to determine if L. kindtii mean size and abundance differed vertically and horizontally, and to determine if their distribution differed under different turbidities and water temperatures. L. kindtii were sampled in six periods from 22 July to 10 September 2002 using a bongo net towed at set depths. Abundance displayed a patchy, highly variable distribution among periods and habitat types and among samples within periods and habitat types. Greatest abundances were found within the reservoir habitat type. Diurnal phase was not significantly related to L. kindtii abundance at depth. Highest daytime abundances were found at 1.25?m or deeper for five of six sample periods. Highest nighttime abundances were found at 1.25?m or deeper in three of the six sample periods. Significant interaction was found between diurnal phase and depth in five of six periods. In general, higher L. kindtii abundance was observed in association with higher water temperatures and lower turbidities.