和歌山県日置川における中・下流域の大型底生動物群集

Abstract

Macro-benthos communities in the middle and downstream of the River Hikigawa are compared statistically in terms of riverbed types, sampling sites and seasons. More than 90 species of animals inhabit this area, and most of them are aquatic insects. Although the number of taxa, total individual numbers and total biomass tend to be abundant at the Hayase rapids in the middle stream in summer and autumn, their differences in each type of riverbed are hardly detectable downstream and in all sites in winter and early spring. Comparisons of these three measurements among sampling sites reveal significant differences in all riverbed types and seasons. But no correlation is found between these measurements and the horizontal gradient of the riverbed in this area. They also change with the season in most riverbed types and sites. In the main stream, the variance ratios differ significantly at one percent probability levels in all sites, and the maximum amounts are attained between winter and early spring. Simpson's species diversity index does not show any seasonal periodicity when it is compared on the above three bases, although differences between them in terms of sites and seasons are often observed. This result may be mainly caused by the significant positive correlations between the number of taxa and total individual numbers.