The relative importance of natural and anthropogenic factors, especially topographic type, riparian canopy, altitude, temperature and bank protection, on larval chironomid assemblage was investigated in a Japanese basin. To focus on the macro-scale factors, a concrete block, as an artificial substrate, was used for chironomid collection so that sampling regime may be identical among the sites. Partial CCA using sampling month as a covariable revealed that topographic type, riparian canopy coverage, water temperature and altitude were the main factors influencing species distribution. Stempellinella tamaseptima, Polypedilum tamanigrum and five Rheotanytarsus species showed positive, whereas five Cricotopus species showed negative associations with canopy coverage. Some traditional longitudinal zonations of species were still shown. Chironomus flaviplumus and Chironomus yoshimatsui were merely associated with lower reaches. Stepwise multiple regressions of the assemblage indices on the environmental variables were applied. Bank protection and depth showed negative correlations with Shannon diversity H 0 . Both topographic type and depth showed negative correlations with Pielou equitability J. Topographic type (lower reach) and specific conductance showed positive, while bank protection showed a negative correlation with abundance. Species richness was not explained by any variables. As a whole, topographic type was the most directly related factor to chironomid assemblages.

No abstract

Occurrence patterns in relation to sorne environmental factors in river environments were examined among the chironomid species of some subgenera of genus PolyPedilum by a method of identifying male adults emerging from the materials attaching to blocks submerged on the bottom at rapids. In terms of altitude, PolyPedilum Pedestre and R takaoense occurred only in high ()600 m) and low (<300 m) altitude ranges, respectively, among the subgenus Pblypeditum, PblyPedilum. tamahosohige occurred in the largest number in a middle (300-600m} range. Among the subgenus U}resipedilum, P. sp. nr, Pedestre occurred only in a low range. POlypedilum. hiroshimaense occurred in the largest number in a high range, In terms of topographic type.R pedestre occurred only in an Aa (mountainous stream) type among the Ilolypedilum. I]blJipedilum tamaharaki occurred in a larger number in an Aa-Bb (interrnediate type between mountainous stream and rnidstream). Among the [fresipeditum, R paravicops occurred only in Bb 90 pmhoslcm) ranges, respectively, among the llo()LPedilum, PblyPeditum tsuleubaense occurred in a larger number in a middle (45-90ptmhoslcm) range. Arnong the Utesij)edilum, R surugense occurred only in a middle range. jR hiroshimaense and R convictum occurred in larger numbers in low and high ranges, respectively. These results suggest that there are multidimensional habitat-segregations among the species of subgenera POI){Pedilum and Uirestpedilum.

The JapanSociety ofMedicalEntomology andZoology (Med. Entomol. ZooLVol, 49 No. 1p.41-50 1998]

Variations in body size of the suspension-feeding lancelet Branchiostoma belcheri were examined from April 2001 to December 2001 at different water depths of 10-80 m. The lancelets were abundantly collected (220 indiv./dredge) at water depth of 10 m. The maximum size, ranging from 36.8 to 50.4 mm BL, decreased with increasing water depth. However, the minimum size of 7.4-7.8 mm BL, which corresponds to settling size, did not different with water depth. From seasonal changes in the length-frequency histograms, five cohorts were observed at every water depth. The lancelets grew to 44 mm BL at water depths of 10-20 m and to 34 mm BL at water depth of 80 m with four years of life span. Developmental stages of the gonads at an age of two years showed that no individuals had undeveloped gonads at water depth of 10 m, but 82% of them did at water depth of 80 m. The analysis of the stepwise multiple regressions of monthly growth rate on environmental variables showed that chlorophyll a was the best explanatory variable and showed a significant positive correlation with the growth of 1-2 years age groups. These results suggested that variations in the body length were mainly fluctuated by phytoplankton supply.