Volume XX - 1954

The depth below the surface to which green plants are able to penetrate depends primarily on the availability of light, which is essential for photosynthesis. Turbidity, color, and amount of surface disturbance are the prime factors in determining the depth to which sufficient light for photosynthesis will penetrate. Based in large part upon these conditions, green plants occupy what is termed the photosynthetic zone, the upper six to seventeen feet (two to five meters) of water in most lakes. The growth of mosses at a depth greater than 400 feet (122 meters) in Crater Lake is therefore a tribute to the clarity of its water.

Peters grapple used by the authors

Hasler (1938), a member of the naturalist staff at Crater Lake National Park during the summers of 1937 and 1938, states that, "The most startling biological finding at Crater Lake was the collection, by dredge, of green mosses...at the astonishing depth of 394 feet (120 meters). This is the greatest depth that growing green plants have been known to live in any fresh water body." (Hasler, 1937).

Collections made this past summer, using the grapple pictured, confirm and extend Hasler's findings, which indicated that green plants cover a large part of the bottom of Crater Lake down to a remarkable depth. Mosses were collected by the authors from maximum depths of 384 feet (117 meters) in Cleetwood Cove, 410 feet (125 meters) at a point south of Wizard Island, and 425 feet (129 meters) at a place south of the Wineglass. In fact, very few attempts below 110 feet failed to be rewarding in this respect. Material from this 425 foot collection has been identified as Drepanocladus fluitans (Hedw.) Warnst. by Dr. Francis Drouet, Curator of Cryptogamic Botany, Chicago Natural History Museum, to whom appreciation is expressed for making this determination.

These figures do not necessarily represent maximum depths at which mosses occur in Crater Lake. They represent, rather, near-maximum working depths attainable with the 450 feet of cable available for the operations. Two other factors need to be considered in interpreting these figures: (1) the difficulty in locating a portion of the generally steep-sloping lake bottom that allows full use of the equipment, and (2) the difficulty in then maneuvering a small boat so as to remain over such a spot.

The minimum depth at which mosses occur in Crater Lake appears to be more definable. Hasler (1938) found no moss above a depth of sixty feet, and the least depth at which we recovered mosses was eighty-five feet. In some areas, such as at Cleetwood Cove and Eagle Cove, no mosses were obtained at depths less than 110 feet.

It is difficult to suggest valid reasons for such findings. Wave action could be a factor, although the situation at Fumarole Bay, which is quite protected and in which mosses are not found at lesser depths than elsewhere in the lake, would seem to preclude this explanation. Another possibility is that the species may be light intolerant. Collections of mosses made from a log (Brode, 1938; Fairbanks, 1953), called the "Old Man of the Lake," that has been floating about the lake for many years in a vertical, "dead-head" position, would seem to lend doubt to such a conclusion. It appears that this problem will not yield to simple explanation and will have to await further investigation.

References

Brode, J. Stanley. 1938. The denizens of Crater Lake. Northwest Sci. 12(3):50-57.

Fairbanks, C. Warren. 1953. The Crater Lake community. Nature Notes from Crater Lake 19:21-25.

Hasler, Arthur D. 1937. Preliminary report on bottom flora and fauna of Crater Lake. (MS. in Crater Lake National Park Library).

-----. 1938. Fish biology and limnology of Crater Lake, Oregon. Journ. Wildlife Management 2(3):94-103.

Frederick V. Coville (1897) reported that in 1896, "The Lake itself is wholly devoid of aquatic vegetation. No algae, no mosses, and no aquatic flowering plants were found in its water." Crater Lake is now known to support a large number of small (microscopic) animals and plants, and the lake bottom, at depths of 60 to 425 feet, appears almost everywhere to have a thick covering of mosses. The types of aquatic flowering plants thus far discovered in Crater Lake, however, are limited to a very small number.

During the summer of 1954, six different species of flowering plants were observed in the lake. Water buttercup, Ranunculus aquatilis L. var. capillaceus (Thuill.) DC., occurred in several large beds eight to ten feet below the lake surface in the northeastern corner of Fumarole Bay, on the western side of Wizard Island. One solitary emergent plant was found close to the shore of the island. This individual bloomed on August 17.

Water buttercup was collected by Brode (1938) near this same location in 1935. Until this summer, it was regarded as the only aquatic flowering plant in Crater Lake.

Two other plants were growing, both submersed and emergent, in the same part of the lake. A member of the mustard family, tentatively identified as Pennsylvania bitter-cress, Cardamine pennsylvanica Muhl., was rooted as much as a foot below the surface. When first observed, early in August, none of the fifteen to twenty individuals found had emergent leaves or stems. Later that month, the leaves of several plants had extended above the water. High winds in early September severely damaged these plants, and when last observed, on September 10, none had flowered. Two plants, however, which had been transplanted to an aquarium at Park Headquarters produced flowers and fruits.

Baltic Rush near Wizard Island. Photo by C. Warren Fairbanks.

This little mustard had an enormous amount of root development for its size. This feature is undoubtedly important in its moderate success, thus far, on the rocky and inhospitable bottom of Crater Lake. The tuber- like root and its many smaller rootlets were, in fact, not rooted in the usual sense at all but were merely entwined about these rocks.

Rather extensive groups of a rush, Juncus balticus Willd., were rooted below the water in at least four different spots in or adjacent to Fumarole Bay. In each of these areas, part of the rush growth is above water. This Baltic rush, in common with most other rushes, multiplies both by seeds and by runners (rhizomes) under soil or water. Hence, its spread from the damp, semi-aquatic shore into the water - or vice versa - could be expected. It is likely that the roots of the highest plants were submersed during the spring high-water level (cf. Fairbanks, 1954). Both the Baltic rush and the Pennsylvania bitter-cress are found in several other locations in the park outside the caldera and are common in wet places along the Pacific Coast.

At least one species of willow, Salix coulteri And., and the red elderberry, Sambucus racemosa L. var. callicarpa Greene, were occasionally found near and in the water. Both of these are sometimes considered to be aquatic plants since they are water tolerant; one Coulter willow is rooted in eight feet of water. There is evidence, however, that they are being drowned by the increase in water level since 1940. At that time, the lake was slightly more than fourteen feet below its present average elevation of 6,176 feet above sea level (Fairbanks, 1954). There were no young plants noted in the water.

Fennel-leaved pondweed, Potamogeton pectinatus L., was found growing in abundance on the bottom at depths of ten to fifteen feet in a channel near the westernmost extension of the Wizard Island block lava flow into Skell Channel. The portion of this channel supporting this pondweed would undoubtedly have been a pool in 1940 when the lake was fourteen feet below its present level. Since the bottom is now twenty feet below the surface and has a layer of diatomaceous ooze as much as three inches in thickness on top, a long period of submersion is suggested.

Sago, or fennel-leaved, pondweed is cosmopolitan in its distribution, being found in fresh or saline waters from sea level to 7,000 feet in elevation. Although this plant has not been observed previously in Crater Lake National Park, its presence now is not particularly surprising.

This pondweed is considered to be an important food for waterfowl. There is a small, pea-sized tuber at the base of its stem. It is abundant in many ponds and lakes, such as Upper Klamath Lake only a relatively few miles to the southeast. It may, therefore, be fairly safely assumed that ducks and other water birds occasionally carry around such plants on their feet. Eventually a hitch-hiking pondweed could be expected to drop off into Crater Lake in a location which would provide protection from wind and wave action and which would supply a sufficiently favorable bottom for its establishment and reproduction. Of course, it may have arrived in some entirely different manner.

In this connection, it might be mentioned that Crater Lake at present has very few areas where the bottom is both sufficiently shallow and adequately protected to offer a favorable environment for colonization by aquatic flowering plants. It is true that a shelf has developed under much of the lake edge at the base of the rim wall. However, the major factors responsible for the formation of the shelf -- falling debris from the steep wall above, and wave action -- tend to deter the successful establishment of plants. These are undoubtedly among the more important reasons why the waters adjacent to Wizard Island support most of the aquatic flowering plants found in Crater Lake. The greater stability of the debris near the shore of Wizard Island greatly reduces the amount of disturbance caused by this factor in the underwater shelf around the island. The greater irregularity of the shore line around Wizard Island - with its small but numerous inlets, bays, promontories and off-shore islets, especially in the Fumarole Bay area -- undoubtedly contributes toward a considerable reduction in the intensity of wave action. These two factors would therefore tend to produce around the island areas much more favorable to the establishment of aquatic flowering plants than any area along the shore of the rim wall.

The concentration of these plants in the Fumarole Bay area of Wizard Island is no doubt also a result of the greater accessibility of this western side of the island to plants. Wizard Island here approaches most closely the wall of the caldera itself, the distance across Skell Channel at its narrowest being approximately three hundred feet. The water between the island and the caldera shore is also at its shallowest in this channel. Changes in lake level would therefore operate most effectively here in exposing additional land surface which could act as a passageway for migrating plants.

It has been suggested many times (Shelford, 1918) that the quantity of plant and animal life increases with the age of water bodies, especially where the outlet is small. If this is true, the number of aquatic flowering plants in Crater Lake could be expected to increase steadily and perhaps quite rapidly. This would be due not only to the fact that it is a relatively young lake, but also to the fact that the lake level may remain fairly constant, with the exception of seasonal variations, for several successive years. This latter factor would perhaps tend to operate in the same manner as a small outlet and, in any case, would contribute favorably to the establishment of new species.

Thus it is possible that Coville's reference to a complete lack of plants in Crater Lake, although undoubtedly not strictly true, may have been very nearly so in 1896. There is ample evidence, from other regions that have been formed by volcanic eruptions, for radical changes of this sort within a period of fifty years.

Except for the trees that come down to the shore line on parts of the caldera wall and on Wizard Island, the lake appears -- even after some exploration -- to be quite barren. Who would suspect that from less than one hundred feet to more than four hundred feet below the surface there grows a lush mat of mosses in every place in which we have grappled so far? Furthermore, how many would realize that these mosses harbor an even greater number of smaller plants -- algae -- and animals?

Specimens of these aquatic plants are deposited in the herbarium at Park Headquarters, Crater Lake National Park. Perhaps you would like to know some of them better but will not be able to meet them first-hand in the lake. You will be welcomed at the park herbarium if you are particularly interested in these plants.

References

Brode. J. Stanley. 1938. The denizens of Crater Lake. Northwest Sci. 12(3):50-57.

Coville, F. V. 1897. The August vegetation of Mount Mazama, Oregon. Mazama 1(2):170-203.

Fairbanks,. C. Warren. Crater Lake waters. Nature Notes from Crater Lake 20:31-35.

Shelford, V. E. 1918. Conditions of existence. In: Ward, H. B., and G. C. Whipple. Fresh-water Biology. New York, John Wiley & Sons, Inc. ix, 1111 pp.