Although lakes and streams are fundamentally different environments, aquatic ecologists have long recognized similarities in species composition and ecological processes between mountainous headwater streams and high elevation oligotrophic lakes. The water penny beetle, Eubrianax edwardsii (Psephenidae), occurs in a variety of lotic habitats in the Pacific Coastal region. Previously, the only known lentic populations were described in 1992 from Gold Lake and Goose Lake, two lakes in the Lakes Basin, northern Sierra Nevada, CA, a region of dozens of high altitude (2000m) glacial lakes. Aside from a long history of inconsistent fish stocking and irregular fish and amphibian surveys, no formal surveys of aquatic fauna have been performed in the Lakes Basin. This study of lakes in the Lakes Basin aimed to: (1) survey the benthic invertebrate community, (2) identify the occurrence and distribution of lentic populations of E. edwardsii, and (3) determine whether there were differences in invertebrate communities amongst lakes with different flow regimes. During the summer of 2015 and 2016 we performed timed sampling of benthic macroinvertebrates from rocky shorelines of ten lakes in the Lakes Basin by hand-picking animals from cobble and boulder.
We reconfirmed the presence of lentic populations of E. edwardsii in the two lakes, as well as in three additional lakes in the Lakes Basin: Upper and Lower Salmon, and Silver. During the course of this study we learned that E. edwardsii has also been found at two of 600 surveyed lakes in the central Sierra Nevada, 200km south of Lakes Basin (Roland Knapp, personal communication). Additionally, we documented larvae of the wood-boring caddisfly, Heteroplectron californicum, a species only previously known from mountain streams in CA and OR, in three lakes. The occurrence of two stream-dwelling insects in lakes of the Lakes Basin suggests that the lakes provide similar habitat conditions to streams, such as high oxygen levels, coarse substrate, and oligotrophic conditions (e.g. low primary productivity). Also notable was the occurrence of chironomid midges and other invertebrates living on the organic cases of the caddisflies Limnephilus and Mystacides. We did not see evidence of parasitism; rather, we suspect a phoretic association. Ongoing work is investigating genetic differences among E. edwardsii populations across the Sierras, the nature of the association between the invertebrates on the cases of Limnephilus and Mystacides, and the distribution of H. californicum.