Large suprabenthic Daphnia middendorffiana from an alpine lake in the Canadian Rocky Mountains

Exceptionally large (up to 4.0 mm) Daphnia middendorffiana were collected w ith a bottom-closing net while sampling benthos in Pipit Lake, Alberta. Suc h large D. middendorffiana have not been observed in plankton samples colle cted from the lake over the past 30 years, nor have such large individuals been reported in the literature. Stable nitrogen isotope ratios (delta(15)N ) of the large Daphnia were 4.5 parts per thousand higher than smaller Daph nia from higher in the water column, indicating that the spatially separate d Daphnia may use different food sources. The large Daphnia had Hesperodiap tomus resting eggs and nauplii in their guts, while the smaller Daphnia hig her in the water column had mainly phytoplankton in their guts. Our finding s highlight the need to use several different kinds of sampling gear to com pletely assess the fauna of a lake.