Ecological Studies of the Sand-Dwelling Community of an East Texas Stream

Abstract

Between February 1976 and January 1977, an ecological study was made of sandy riffle areas of Mill Creek, Newton County, Texas. The psammonic community in the main channel of Mill Creek consisted of midges, oligochaetes, flatworms, micro-crustaceans, nematodes and tardigrades. The six dominant psammonic taxa with their annual mean densities and standard deviations (102 × animals / m2) were Aeolosoma spp. (1455 ± 3448), Catenula sp. (188 ± 605), Parakiefferiella spp. (307 ± 1169), Nematoda (43 ± 105), Robackia demeijerei (20 ± 30), and Polypedium spp. (20 ± 148). The following taxa were also present in descending order of abundance: Eucyclops agilis, Macrobiotus sp., Hexagenia limbata, Tanytarsini and Parastenocaris sp. Psammon densities were lowest in summer and highest in winter. Densities were highest in mid-riffle stations of upper and lower Mill Creek, and between mid-riffle and margin. Densities were lowest at the riffle's margin, pool and the Copperas Creek stations. Highest densities may be associated with intermediate water velocities which are slow enough to permit adequate deposition of detritus, but fast enough to prevent silt clogging and deoxygenation of sand interstices. Parastenocaris sp., Rhynchataloma falcata, Tanytarsini, and Nematoda did not differ significantly in vertical distribution (α=0.05). Aeolosoma spp., Robackia demeijerei, Parakiefferiella spp., Polypedilum spp., Catenula sp., Eucyclops agilis and Hexagenia limbata populations decreased with sand depth, while Macrobiotus sp. density increased with sand depth.