Yo Miyake

Relationships between length and weight of freshwater macroinvertebrates in Japan

Relationships between weight (W; dry weight) and length (L; head capsule width, total body length or head carapace length) were examined in 31 Japanese freshwater macroinvertebrate taxa, using the form W = aLb. The relationships were expressed as data of the lowest taxonomic level and data of higher taxonomic levels. The length–weight relationships obtained in this study were similar to those obtained in North America and Europe at the lowest taxonomic level, whereas they could be different from those obtained in North America and Europe at the higher taxonomic levels. We suggest that researchers should make their own regressions for a target taxon or use the regression for the same taxon as possible lower taxonomic level in the local area.

The role of the hyporheic zone for a benthic fish in an intermittent river: a refuge, not a graveyard

In lotic systems, the hyporheic zone has been suggested as a potential refuge for aquatic organisms during disturbances (hyporheic refuge hypothesis). However, the supporting evidence is unclear, especially regarding the survival of hyporheic refugees and their contribution to the recovery of post-disturbance populations. Moreover, few studies have focused on the importance of the hyporheic refuge for aquatic vertebrates such as fish. In this study, we present evidence that the hyporheic zone acts as a refuge for a small benthic fish (Cobitis shikokuensis) following surface drying in an intermittent river. We examined its survival during and recolonization after dry periods by direct hyporheic sampling and mark-and-recapture surveys. When the streambed dried, hyporheic sampling was conducted 58 times across 33 locations in the intermittent reach and 31 individuals of C. shikokuensis were captured from extracted hyporheic water. Mark-and-recapture surveys revealed that recolonizers after re-wetting included C. shikokuensis individuals that had survived dry periods in the hyporheic refuge. The condition factor of C. shikokuensis significantly declined after dry periods, suggesting that most recolonizers suffered from physiological stress, probably within the hyporheic refuge. These results clearly support the long-debated, hyporheic refuge hypothesis, and provide a striking example of the critical role of the hyporheic zone in population maintenance of lotic organisms.

Effects of frequent streambed disturbance on the diversity of stream invertebrates

We conducted a field experiment to reveal the effects of frequent streambed disturbance on the diversity of stream invertebrates in a local habitat patch in a Japanese stream. We used wire mesh baskets as experimental substrata and manipulated five levels of disturbance frequency (every 2, 4, 8, 16 or 32 days) in order to describe the pattern of the diversity of the stream invertebrates under different disturbance frequency and to explore possible factors generating the pattern. The total abundance and taxon richness recovered during 8-day and 2-day periods between each experimental disturbance, respectively, indicating that the stream invertebrates were highly resilient to disturbance due to their high mobility. The evenness of the invertebrate community was high in streambed patches with frequent disturbance. Patterns of the absolute abundance among the different disturbance frequency treatments differed substantially among nine common taxa. The absolute abundance of the most common taxon, Chironominae, was low in streambed patches where the disturbance frequency was high and intermediate, suggesting their low colonizing ability owing to their low mobility, compared with other common taxa. These results suggested that the diversity, in terms of evenness, of stream invertebrates in a local habitat patch is maintained by frequent streambed disturbance when the most common taxon has low colonizing ability. Our study demonstrated that differences in colonizing ability, caused by different mobilities, among community members may have a prominent importance when investigating the relationships between disturbance frequency and the diversity of organisms that have high mobility and actively colonize an opened patch.

Input, retention, and invertebrate colonization of allochthonous litter in streams bordered by deciduous broadleaved forest, a conifer plantation, and a clear-cut site in southwestern Japan

In headwater streams, conifer plantation forestry may affect stream communities through the quantity and quality of basal resources (allochthonous litter). We compared (1) the seasonal patterns of litter input from the riparian canopy, (2) those for the abundance of benthic and drifting litter in streams, and (3) the density of litter-associated invertebrates among streams bordered by deciduous broadleaved forest, a plantation of Japanese cedar (Cryptomeria japonica), and a clear-cut site, to extract the characteristics of conifer-plantation streams in terms of litter dynamics and benthic invertebrates. The results illustrate differences in litter input and in-stream processes between the broadleaved and plantation sites, although the total annual inputs from canopy were similar. In the broadleaved site, high litter storage was limited to winter, probably because pulsed inputs of litter in autumn were retained on the streambed but rapidly processed. In contrast, litter input was more constant at the plantation site, and litter was stored throughout the year. Although the litter-patch-specific density of total invertebrates was similar between the broadleaved and plantation sites, estimates of the reach-scale, habitat-weighted density considering differences in the coverage area of litter patches revealed considerable differences. Although the habitat-weighted density of total invertebrates was lower at the plantation site than at the broadleaved site in winter, it was noticeably higher at the plantation site in summer, owing to the seasonal stability of benthic litter abundance. Our results emphasized the importance of considering the spatiotemporal availability of benthic litter when assessing the effects of conifer plantations on stream ecosystems.

Comparison of DNA metabarcoding and morphological identification for stream macroinvertebrate biodiversity assessment and monitoring

Conventional morphology-based identification is commonly used for routine assessment of freshwater ecosystems. However, cost and time efficient techniques such as high-throughput sequencing (HTS) based approaches may resolve the constraints encountered in conducting morphology-based surveys. Here, we characterized stream macroinvertebrate species diversity and community composition via metabarcoding and morphological analysis from environmental samples collected from the Shigenobu River Basin in Ehime Prefecture, Japan. We compared diversity metrics and assessed both approaches’ ability to evaluate the relationship between macroinvertebrate community and environmental variables. In total, we morphologically identified 45 taxa (3 families, six subfamilies, 31 genera, and five species) from 8,276 collected individuals from ten study sites. We detected 44 species by metabarcoding, with 35 species collapsed into 11 groups matching the morphologically identified taxa. A significant positive correlation between logged depth (number of HTS reads) and abundance of morphological taxa was observed, which implied that quantitative data can be used for subsequent analyses. Relatively higher estimates of alpha diversity were calculated from the metabarcoding data in comparison to morphology-based data. However, beta diversity estimates between metabarcoding and morphology data based on both incidence and abundance-based matrices were correlated proving that community differences between sampling sites were preserved in the molecular data. Also, both models were significant, but metabarcoding data (93%) explained a relatively higher percentage of variation in the relationship between community composition and the environmental variables than morphological data (91%). Overall, we present both the feasibility and limitations of HTS-driven estimations of taxonomic richness, community composition, and diversity metrics, and that metabarcoding was proven comparable and more sensitive against morphology-based analysis for stream macroinvertebrate biodiversity assessment and environmental monitoring.