THE STRUCTURE OF DOMINANT INVERTEBRATE ASSEMBLAGES IN A SMALL SOUTHEASTERN STREAM

Invertebrates were collected following near-average, extremely low, and above-average discharge in the winters of 1987, 1988, and 1989, respectively, in Luxapalila Creek, Mississippi and Alabama. Total invertebrate density was lower in pools (mean = 7,364, range = 5,427-12,561 individuals/sq m) than in riffles where it was also more variable (mean = 15,964, range = 9,662-28,820 individuals/sq m). There were no significant seasonal density differences among pools (p > 0.05). In samples collected during the fall, total density in riffles was two times higher than in pools. Following high discharge in December-February 1988-89, there were no significant density differences between pools and riffles. Interhabitat differences in chironomid and oligochaete species composition existed in Luxapalila Creek; seasonal periods of high water had a greater effect on invertebrates in riffles than pools.