The Ecology of the Macroscopic Bottom Fauna in Lake Texoma (Denison Reservoir), Oklahoma and Texas

Abstract

With the advent of extensive flood control and hydroelectric projects, the field of limnology has had a new and imperfectly understood facet added in the form of numerous impoundments. While several studies have been made on smaller impoundments, few have been done on the larger and deeper ones of the Southwest. This is particularly true of studies of benthic organisms, as Greenbank's (1937) results from Elephant Butte Reservoir in New Mexico were the only ones suitable for comparison with the work presented here. Emphasis of this study has been on horizontal and vertical distribution and seasonal succession of the macroscopic bottom animals. A cursory examinatiotn of the other limnological features was also made (Sublette, 1955). The major community which Klugh (1923) referred to as the lake bottom association has commonly been divided by limnologists into the littoral, sublittoral, and profundal zones. These zones are defined as follows: littoral, from the lake margin to a 'depth which marks the lakeward limits of the rooted aquatic vegetation; sublittoral, the area bounded by the littoral above and the profundal below; and profundal, roughly, the area of the bottomn in contact with the hypolimnnion. An examination of the literature shows the extreme variability of zones so described, not only between different bodies of water, but within a lake itself. This variability is primarily the result of two factors. One of these is the lakeward extension of rooted aquatic plants. It has been demonstrated, (vide Welch, 1952) that different plant species have differing depth tolerances. Are two bodies of water, similar in every respect except that one has a shallow water and the other a deep water flora, to be considered as having entirely different littoral zones? The other variable factor is that of hypolimnion depth distribution. When a hypolimnion iS present it varies in depth from season to season. Are the profundal zone limits then to change with the fluctuations of the hypolimnion? And what of the lake which rarely or never has a hypolimnion? Many writers, in order to avoid such poorly defined categories, have instead used the categories mentioned (littoral, sublittoral, and profundal) but have defined them by stating the exact depth limits of each zone. A more logical system would be to designate the zones on the basis of sediment substratum as has been pointed out by Pearse (1939) for marine communities. The two major divisions, littoral and profundal, can readily be recognized as major communities since each exhibits a very different assemnblage of organisms. What is not usually recognized is thait within each major community (zone) there are minor communities. Observations on these minor 371