Abstract
Transectional distributions of chironomid larvae were investigated at 14 sampling stations covering the estuaries of 7 rivers, all flowing into Hiroshima Bay. Benthic sediments were quantitatively sampled at 3 different levels along the transectional line at each station, i. e., a submerged level at ebb (S), a water level at ebb (Z) and a dried-up level at ebb (D), and emerging male adults from the sediment samples were identified. A total of 183 males, belonging to 31 species, were collected. Procladius simplicistilus, Rheopelopia eximia, Cricotopus bicinctus, C. bimaculatus, Paratrichocladius rufiventris, Chironomus salinarius, Dicrotendipes enteromorphae, Nilothauma brayi and Tanytarsus yunosecundus occurred only in S. Chironomus nipponensis, Polypedilum masudai and Stictochironomus pictulus occurred only in Z. Cricotopus sylvestris, Paratendipes tamayubai, Polypedilum japonicum, Cladotanytarsus vanderwulpi and Tanytarsus unagiseptimus occurred only in D. On the other hand, Chironomus kiiensis, C. yoshimatsui and Dicrotendipes flexus occurred in all the levels. These results suggest that there are transectional habitat-segregations in estuaries among the species in relation to their resistance to salinity and dessication.
