A one-person submersible was used to examine the vertical distribution of the deep-water moss
Drepanocladus aduncus (Hedw.) Warnst in Crater Lake (Oregon). Living specimens were found
attached to sediment and rocks at depths between 25 m and 140 m. Dense beds of the moss
were observed at depths between 30 m and 80 m, a region that corresponded roughly to the
zone of maximum primary production by phytoplankton. The moss population supported a diverse
assemblage of epiphytic algae, of which the most abundant genera included Cladophora,Oedogonium, Rhizoclonium, Tribonema, Vaucheria, and the diatoms Cocconeis,
Cymbella, Epithemia, Fragilaria, Gomphonema, Melosira, Navicula, and Synedra. Chemical and
physical data supported the hypothesis that the lower limit of distribution of the moss is
determined by light limitation, whereas the upper limit is related to the availability of nutrients, particularly nitrate-nitrogen and trace elements. Deep-water videotapes of the moss population indicated that D. aduncus with its epiphytic algae was abundant enough in regions associated with the metalimnion and upper hypolimnion to have a potential influence on the nutrient dynamics of the Crater Lake ecosystem. Although the maximum depth at which living bryophytes occur in Crater Lake is similar to that found for Lake Tahoe, conditions in Lake Tahoe allow the growth and survival of a much more diverse assemblage of bryophytes and charophytes than is present in Crater Lake.
