The Benthic Invertebrate Standing Crop and Diversity of a Small Desert Stream in the Big Bend National Park, Texas

Abstract

The invertebrate benthos of Tornillo Creek was analyzed in terms of standing crop, biomass, and species diversity. Numeric standing crop was highly variable among seasons due to physical factors such as scouring and to biological factors, particularly emergence. The mean standing crop was moderately high com- pared to other flowing ecosystems. Biomass was variable among seasons also, but an additional contributing factor was major growth in several populations. The biomass was similar to other running waters. Species diversity, using both numbers of individuals and biomass units was moder- ately high indicating a non-impacted community. Diversity using biomass did not vary as greatly among seasons as diversity using numbers of individuals. There is correlation between the occurrence of certain species of algae and the invertebrate community as indicated by an increase in biomass and species diversity. There have been few studies of natural permanent aquatic eco- systems in the desert southwestern United States (Cole 1966). Tor- nillo Creek, Big Bend National Park, Brewster Co., Texas, is typical of the infrequent small streams of this area. Because of its size, fish populations are small (Hubbs and Wauer 1971) and most of the life is associated with the substrate. The benthos has not been described ecologically. The purpose of our study was to describe quantitatively the benthic community of Tornillo Creek. Factors affecting seasonal distribution, standing crop, and diversity were used in the analysis of this small community. 1 This paper is a part of the limnological survey prepared for the Office of Natural Science, Southwest Region National Park Service over a contracted area from Hot Springs to Boquillas Canyon completed Novrember, 1975.