Exploration of the bottom of Crater Lake in August 1988, using a one-person submersible provided a unique opportunity to observe and collect benthic fauna and flora directly off the lake bottom. Several oligocheates were collected from the soft mud surface. One dive was dedicated to exploring the caldera walls for moss (Drepanocladis) and periphyton. Moss was observed at 253 meters (about 759 feet deep), and a sample ws collected at a depth of 221 meters, or 663 feet. The sample extended the known depth of the moss by about 100 meters, and this is probably a world record depth. Periphyton ws observed on the caldera walls to a depth of 147 meters, or 441 feet, but no samples were collected.

The moss sample ranged in color from bright green through greenish golden to a dark brownish red. The cells of the axes and "leaves" of green axes exhibited numerous and prominent chloroplasts. The plastids in plants that had aged and darkened were impossible to discern. The cells of the darker leaves appeared to have reduce cell contents, including reduced numbers of plastids. The leaves of the darkest axes had usually lost their tips, and commonly, all of the lamina had eroded except for the very base of the leaf. Three means of vegetative reproduction were observed. No sexual or asexual reproduction was observed.

The moss sample supported a rather uniform epiphytic flora as well as some loosely entwined filaments. The latter consisted of and unbranched green alga Rhizoclonium and a branched siphonaceous alga Vaucheria (Xanthophyceae). The epiphytes were a filamentous diatom Melosira and three species of green algae, two Oedogonium species and a Bulbochaete. In addition, there were a number of pennate diatoms attached to the primary leaves of the moss and to a less extent to Rhizoclonium, Melosira, and Vaucheria.

A sparse fauna was found in the moss sample. This included a single tartigrade, two unidentified nematodes, two species fo rotifer, probably Collotheca and Philodina, several species of ciliates, including Strichotricha and Vorticella, and midge larvae.

A rock was collected at 379 meters, or 1,137 feet deep, and was examined in the laboratory, and a single living specimen of epilithic algae was found. Although it was impossible to remove the speciment from the rock, it was photographed and tentatively identified as Tribonema. This appears to be a world record depth for epilithic algae in fresh water.

The great depths at which plants were found living in the Lake is an important discovery to the ten-year limnoligical assessment of Crater Lake. Such growth is probably an integrated measure of water clarity. Since small changes in turbidity could have substantial impacts on the amount of available light at these great depths, documentation of the floral assemblages and their depth distributions provide very importatn baseline information for future monitoring of the clarity of Crater Lake.

by: Gary Larson, Oregon State University
with contributions by: H. Phinney, D. McIntire, S. Loeb, M. Buktenica, N. Anderson, S. Earle

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