The Crater Lake Community
By C. Warren Fairbanks, Assistant Park Naturalist
Probably the most asked question concerning Crater Lake is "Are there any fish in the lake?" To answer "yes" is easy. Such a reply, however, calls to mind the question of what they use for food. This, in turn, leads to a discussion of conditions which make it possible for fish to live and maintain themselves in Crater Lake.
Crater Lake rests in an unusual setting in comparison with most bodies of fresh water. It lies in the top of an ancient mountain - - old as man reckons time, but geologically recent - - the upper 5000 feet of which was destroyed about 6450 years ago. This destruction was in nature of a collapse which dropped the top of the mountain into a great void within its lower reaches and produced a cauldron - - or "caldera," in the geologist's terminology - - nearly 4000 feet deep and from four to six miles in diameter.
Preceding the collapse, a brief series of gigantic pumice eruptions withdrew great amounts of material from below the mountaintop and contributed to formation of the mammoth chamber. Some of these outpourings rushed down the slopes as flaming avalanches of gas-charged lava, each pushed along by its own jet-propelled impetus. Aside from filling stream and glacier-cut valleys, they engulfed and destroyed the forests and all other life, effectively sterilizing the area for miles around. Incidentally, the engulfed forests, through the medium of radioactive carbon, give us our best evidence as to the date of these last eruptions.
Since the collapse, precipitation has filled the cavity to a depth of nearly 2000 feet with water of great clarity and pureness. Its salt content is less than one-sixth that permitted for drinking purposes. Its bacteria count, even in parts where recent storms had carried large quantities of sediment into the lake, was found to be exceedingly low. The shores and bottom are rocky and the lake bed drops rapidly into deep water. There is no true shallow zone or real emergent vegetation. This geologically young lake - - probably less than a thousand years old at its present level - - has no beach worthy of the name.
The unusual setting of Crater Lake in the top of a mountain isolates it from the ordinary channels through which living things migrate and extend their ranges. This old volcanic cone slopes away on all sides. There is no higher ground from which rivers flow into the lake and which could carry living organisms, although there are numerous small cascades whose origins are in melting snows higher within the walls. Neither are there known channeled outlets, which could also serve as pathways of migration. Compared with most lakes, which in reality are only widened streams, Crater Lake is separated from the usual sources of plant and animal population. The life which exists there had to come into the lake by extraordinary means- - the hard way. There was no readily accessible reservoir.
It is interesting to conjecture just how life did come to Crater Lake Briefly, many lower plants and animals pass into stages of existence which are resistant to drying, freezing, and other conditions inimical to normal active life. Frequently, such inactive stages are associated with reproductive processes and involve eggs or spores which can renew activity at some later time when conditions are right. The shallow vernal pond which appears each spring, blooms rapidly and abundantly with diverse plant and animal life, and completely dries up later each summer is an example of this phenomenon. Since many of the forms found in Crater Lake have such inactive stages, it is easy to understand how they came to be there. Bits of mud clinging to the feet of bird could have brought many of them. Some could even have been carried by wind. Others could have been introduced with planted fish.
The Crater Lake community is complex. While the number of forms is small compared with many lakes, among the animals are representatives of most groups found in other fresh waters. In considering the community, however, the green plant is the key to its existence. As is true elsewhere, the green plant with its almost magic chlorophyll supplies all the energy used by animals. It alone has the unique ability to trap energy from the sun and make it available to other living things. It does this by combining two simple substances, carbon dioxide and water, to form grape sugar which is rich in tied-up energy.
This energy is passed on in one form or another to animals and some other plants. The fish - - or man, who eats the fish - - thus derives its very existence, perhaps through a long line of progressively smaller animals, from the simple green plant which started the processes. The biologist calls this a food chain, with the green plant at one end and the large animal at the other. This is the sort of relationship which makes it possible for fish to live in Crater Lake.
Of the green plants in the lake the most important, and practically the only ones, are the algae. These simple, essentially one-celled plants exist singly or in small groups that ordinarily can be seen only with the aid of a microscope. Some are grouped into long thread-like filaments. The filaments in turn may be gathered into jelly-like balls or masses large enough to be seen with the naked eye.
It would be difficult to assign relative importance to the members of this large plant group. Surely those classed as blue-greens, having a blue pigment which partially masks the green of the chlorophyll, appear most abundantly. One of these, Nostoc, is found growing in ball-like masses attached to rocks and among mosses. Other blue-greens are Oscillatoria, Calothrix, and Chroococcus (Brode, 1938). Other important algae, however, are certain filamentous greens, for example, Mougeotia and Zygnema. Rocks and logs along the shore show a conspicuous growth of Cladophora (Brode, 1938) and Ulothrix. Diatoms comprise the third important algal group. They are so abundant in "Fumarole Bay," on the western side of Wizard Island, that the glass cases which enclose the living portion of this one-celled plant have formed, as countless numbers have died and settled to the bottom, a thick floor of diatomaceous ooze. This, of course, does not exhaust the algae found in Crater Lake but is only representative.
Mosses also are represented in the waters of the lake. Near Wizard Island, Fontinalis and Drepanocladus form a very thick mat on the bottom at a depth of 394 feet (Hasler, 1938) - - an indication of the great clarity of the water, which permits light to penetrate to such a depth in sufficient quantity for these plants to carry on the essential process of food manufacture.
Fontinalis also occurs on the "Old Man of the Lake," the only place it is found near the surface (Brode, 1938). During the summer of 1953, a collection of several moss specimens was made on the "Old Man of the Lake." Recent examination of these specimens by Dr. Henry S. Conard, Grinnell College, Iowa, showed all the material to be Scleropodium obtusifolium (Hook.) Kindb. It would appear, therefore, that this specie. is now the most abundant, if not the only, moss in this unusual habitat. Appreciation is expressed to Dr. Conard for making this identification.
According to Brode (1938), the only flowering plant growing rooted in the lake is the water buttercup (Ranunculus aquatilis capillaceus), found at depths of five to fifteen feet.
These, then, are the green plants which form the base of the great pyramid at the apex of which are the fish which dominate the waters.
Green plants alone, however, would not support a population of rainbow trout or sockeye salmon. These animals require a "meat" diet. Between them and the plants there is of necessity at least one intermediate animal which feeds upon plants and serves to convert plant materials into animal substance. Several inhabitants of Crater Lake serve in this capacity. Some feed directly upon the living plants while others function as scavengers which utilize dead organic matter for food. Hubbard (1934) lists five such converters. The most important is the "bloodworm, " or midge larva, which feeds almost exclusively upon algae. While some larvae are taken by fish, the pupal stage, since it is less active, appears to be a more important component of the fish diet. Caddis fly pupae are also found in some abundance in fish stomachs.
Snails, which feed on diatoms as well as upon dead animal matter are often taken by fish. Chief Ranger L. W. Hallock reported the catch of a 23-inch rainbow, the major food item of which was the snail. This returning of dead animal matter directly to living flesh is an important short cut in the food cycle.
Certain small relatives of the crayfish which live in the lake also play their part in food conversion. Daphnia, the so-called "water flea," is very tiny--it measures perhaps 2mm., 1/12 inch, in length--but exists in rather large numbers. Kemmerer et al. (1923) state that they are found mostly between about 250 and 300 feet or more below the surface. The preferred food item of these small crustaceans is the diatom. They, in turn, are of primary importance to the fingerling fish and often make up a considerable portion of the food of larger fish. Brode (1938) reported 7500 in the stomach of one fish. The freshwater shrimp, Hyalella, also forms part of their diet. The copepod, Cyclops, though not as abundant as Daphnia, plays a similar role as a converter.
Many of the smaller converters are also fed upon by large carnivorous water insects, which then fall prey to fish. Of these intermediate forms, dragonfly nymphs play an important part. While they themselves are seldom taken by fish, adults, as they fly over the water, often are caught by them. Adult whirligig beetles, which live in the water, also are important intermediates.
During the summer months, those fish which feed at the surface take advantage of any food items that may come their way. While no considerable number of fish stomachs were examined this season, those studied-- from fish taken exclusively by casting from shore--had fed predominantly upon terrestrial insects. These consisted of various flies, bees, ichneumons, a great many long- horned beetles, butterflies and dragonflies. A few spiders were also found. Strictly aquatic forms were few and were primarily midge larvae and pupae.
Most of the fish reported were taken by Ranger Joseph C. Hunt. These were largely rainbow trout (Salmo gairdnerii irideus), although a few were sockeye salmon (Oncorhyncus nerka kennerlyi). The former ranged in length from about 12 to 22 inches, while the sockeyes had a maximum of about 12 inches. The fish, therefore, is an opportunist and takes advantage of what may come his way. In this manner he is able to encroach upon food supplies from outside the lake.
Other forms of animal life not of great importance as fish food are also found in Crater Lake. The endemic salamander, the Mazama newt (Triturus granulosus mazamae), occasionally furnishes a meal for a fish. This near relative of the frog, in company with the long-toed salamander (Ambystoma macrodactylum), lives under rocks along the shore.
Water-dwelling annelids, related to the common earthworm, are found in small numbers and sometimes are retrieved from fish stomachs. In a rather cursory examination of the aquatic community on the "Old Man of the Lake," the remains of a hemlock tree with part of its root system below, and about five feet of stump extending vertically above, the water surface and which is carried about the lake by wind currents, there were found two kinds of these annelids. Among other interesting forms in this community were a large number of mites--relatives of the spider. Quite abundant also, were copepods belonging to the harpacticid group. Specific identification has not yet been made. The available literature indicates, however, that this group of microcrustaceans has not been previously reported from Crater Lake.
Fish, as previously stated, are the dominant forms of animal life in the lake. It should be evident that these inhabitants did not enter the lake by natural means. The first planting was made September 1, 1888, by William Gladstone Steel when he released 37 of an estimated 600 rainbow trout "minnows" with which he had started from the Gordon Ranch, 41 miles from the lake. The first trout was caught in 1901. In 1902, and in many years thereafter, other plantings were made by the National Park Service. A number of species were tried but, with plantings discontinued in the early 1940's, the only ones that have persisted and reproduced are the rainbow trout and sockeye salmon.
The Crater Lake community is thus seen, from this brief review, to be a relatively closed community, at present essentially self-sustaining.
Some forms have been introduced artificially. Most of the inhabitants, however, have found their own ways there and have become established as important components which make their own peculiar contributions toward the total economy.
Brode, J. Stanley. 1938. The denizens of Crater Lake. Northwest Sci. 12 (3):50-57.
Hasler, Arthur D. 1938. Fish biology and limnology of Crater Lake, Oregon. Jour. Wildlife Management 2(3):94-103.
Hubbard, C. Andresen. 1934. Fact and fancy about Crater Lake fish. Report submitted to the Research Branch of the National Park Service, March 1, 1934. (MS. in Crater Lake National Park Library).
Kemmerer, George, J.F. Bovard and W. T. Boorman. 1923. Northeastern lakes of the United States: biological and chemical studies with reference to possibilities in production of fish. Bull. Bur Fisheries 39:51-140.
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