VERTICAL-DISTRIBUTION OF A DEEP-WATER MOSS AND ASSOCIATED EPIPHYTES IN CRATER LAKE, OREGON

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 r ocks at depths between 25 m and 140 m. Dense beds of the moss were obs erved at depths between 30 m and 80 m, a region that corresponded roug hly to the zone of maximum primary production by phytoplankton. The mo ss population supported a diverse assemblage of epiphytic algae, of wh ich the most abundant genera included Cladophora,.Oedogonium, Rhizoclo nium, Tribonema, Vaucheria, and the diatoms Cocconeis, Cymbella, Epith emia. Fragilaria, Gomphonema, Melosira, Navicula, and Synedra. Chemica l and physical data supported the hypothesis that the lower limit of d istribution 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 mos s population indicated that D. aduncus with its epiphytic algae was ab undant enough in regions associated with the metalimnion and upper hyp olimnion to have a potential influence on the nutrient dynamics of the Crater Lake ecosystem. Although the maximum depth at which living bry ophytes 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 Cr ater Lake.