Biodiversity Data Journal :
Research Article
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Corresponding author: Keiko Kishimoto-Yamada (kky_kei@yahoo.co.jp)
Academic editor: Samuel James
Received: 15 Jul 2020 | Accepted: 19 Sep 2020 | Published: 29 Sep 2020
© 2020 Keiko Kishimoto-Yamada, Yukio Minamiya
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation:
Kishimoto-Yamada K, Minamiya Y (2020) Earthworm species and density in semi-natural grasslands on rice paddy levees in Japanese satoyama. Biodiversity Data Journal 8: e56531. https://doi.org/10.3897/BDJ.8.e56531
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Earthworms contribute to the sustainability of food webs in the semi-natural grasslands of levees at paddy margins, which are typical components of satoyama, the traditional agricultural landscapes of Japan. Thus far, few studies have focused on earthworm fauna of paddy levees in satoyama. In this study, we investigated earthworm fauna and regional and monthly changes in earthworm density. We found at least 11 species of earthworms living within levees on Sado Island, central Japan. Two endogeic species, Amynthas corticis (Megascolecidae) and Eisenia japonica (Lumbricidae), were dominant in terms of number of adult individuals; these two species appeared in all study regions. We also estimated an average of ~57.4 individuals/m2 for all stages of earthworms in levees, suggesting that rice paddy levees have relatively-high earthworm density. However, such tendencies differed depending on the region. In addition, monthly changes in density were observed in the topsoil of the levees. Our results imply that differences in earthworm assemblages amongst regions and months may influence the availability of food resources for various animals inhabiting satoyama.
agricultural landscapes, Haplotaxida, Lumbricidae, Megascolecidae, Oligochaeta, preys, Sado Island
Terrestrial earthworms are a high-potential food resource for secondary consumers (e.g.
The levees of rice paddies, located at paddy margins and separating paddies from secondary forests, are typical components of satoyama. They are constructed and maintained to retain water in the paddies and to allow the passage of people and transportation of tools (
On Sado Island, central Japan, typical satoyama landscapes occur throughout the island. In addition, a re-introduction programme for the once-extinct Asian crested ibis, Nipponia nippon, has been underway on the Island since 2003 (
This study was conducted on Sado Island, located in the Sea of Japan, approximately 40 km off the coast of Niigata Prefecture (138°E, 38°N; Fig.
Five study regions on the Kuninaka Plain and in Kosado were selected (Fig.
Detailed characterisations for each study paddy and region. See Suppl. material
Study Region | Paddy | Area of paddy (m2) | Farmland consolidation | Mean values of the percentages of each land-cover type (%) within a 100-m radius | Soil properties | |||||
Cultivated land | Deciduous broad- leaved forests | Planted forests | pH (H2O) | Carbon % | Nitrogen % | CN ratios | ||||
I | 1 | 1,023 | 100.0 | 0.0 | 0.0 | 5.4 | 3.62 | 0.33 | 10.87 | |
2 | 613 | none | 80.2 | 0.0 | 0.0 | 5.4 | 3.13 | 0.3 | 10.43 | |
3 | 1,023 | 100.0 | 0.0 | 0.0 | 5.5 | 4.09 | 0.4 | 10.26 | ||
II | 1 | 3,095 | 100.0 | 0.0 | 0.0 | 5.5 | 2.59 | 0.24 | 10.67 | |
2 | 3,855 | done | 100.0 | 0.0 | 0.0 | 5.7 | 2.68 | 0.26 | 10.14 | |
3 | 4,983 | 100.0 | 0.0 | 0.0 | 5.6 | 4.64 | 0.43 | 10.77 | ||
III | 1 | 762 | 39.9 | 4.6 | 55.7 | 5.3 | 3.01 | 0.26 | 11.49 | |
2 | 968 | none | 54.7 | 4.5 | 39.6 | 5.5 | 3.08 | 0.28 | 10.83 | |
3 | 2,980 | 66.9 | 0.0 | 32.7 | 5.5 | 5.19 | 0.41 | 12.6 | ||
IV | 1 | 2,848 | 63.9 | 18.7 | 0.0 | 4.9 | 3.26 | 0.25 | 13.3 | |
2 | 2,537 | done | 81.9 | 0.0 | 18.3 | 5.3 | 4.15 | 0.33 | 12.45 | |
3 | 1,047 | 61.5 | 25.5 | 0.0 | 5.3 | 3.18 | 0.24 | 13.51 | ||
V | 1 | 399 | 39.0 | 16.6 | 19.7 | 5.2 | 2.81 | 0.22 | 12.74 | |
2 | 847 | done | 25.6 | 74.8 | 0.0 | 5.5 | 2.17 | 0.22 | 10.02 | |
3 | 469 | 23.8 | 58.9 | 15.6 | 5.2 | 3.15 | 0.29 | 10.79 |
Sampling was conducted monthly from June to September 2017, which is the irrigation season. On Sado Island, earthworms were frequently fed by the wild crested ibis on paddy levees during this period (
To examine regional and monthly changes in earthworm densities, the densities were compared amongst study locations using the Kruskal-Wallis test and amongst months using the Friedman test, followed by post hoc analysis. Post hoc tests were conducted using the Nemenyi test in the PMCMR package. All analyses were performed using R version 3.3.3 (
Species occurrence data of levee earthworms collected on Sado Island are listed in Suppl. material
The examination of individuals with clitella revealed the presence of eight Megascolecidae species, two Lumbricidae species and one Moniligastridae species at the levees (Table
Functional groups, monthly individual numbers and regional occurrences of adult earthworm species. En: Endogeic species, Ep: Epigeic species
Earthworm species | Functional groups | Month | Area | ||||||||
Jun | Jul | Aug | Sep | I | II | III | IV | V | |||
Megascolecidae | |||||||||||
Amynthas corticis (Kinberg, 1867) | En | 39 | 8 | 6 | 24 | + | + | + | + | + | |
Amynthas aokii (Ishizuka, 1999) | Ep | 0 | 1 | 0 | 0 | + | |||||
Amynthas micronarius (Goto & Hatai, 1898) | En | 2 | 2 | 0 | 0 | + | + | ||||
Amynthas tokioensis (Beddard, 1892) | Ep | 0 | 4 | 3 | 3 | + | + | + | + | ||
Amynthas vittatus (Goto & Hatai, 1898) | Ep | 0 | 0 | 1 | 0 | + | |||||
Metaphire acincta (Goto & Hatai, 1899) | En | 2 | 1 | 0 | 0 | + | + | ||||
Metaphire agrestis (Goto & Hatai, 1899) | Ep | 0 | 0 | 2 | 0 | + | + | ||||
Metaphire hilgendorfi (Michaelsen, 1892) | Ep | 0 | 1 | 0 | 2 | + | + | ||||
Lumbricidae | |||||||||||
Aporrectodea trapezoides (Dugès, 1828) | En | 2 | 0 | 0 | 0 | + | |||||
Eisenia japonica (Michaelsen, 1892) | En | 45 | 39 | 3 | 0 | + | + | + | + | + | |
Moniligastridae | |||||||||||
Moniligastridae sp. 1 | - | 0 | 1 | 1 | 0 | + | + |
The ten species identified in this study can be categorised into two functional groups (
During the study period, 1,292 individuals with and without clitella were collected. The mean density was 21.53 (0–58) individuals/0.375 m2. Amongst the five regions, densities tended to be different (Kruskal-Wallis chi-squared = 22.53, p < 0.001): they were high in the Areas I and II, compared to Areas III–V (Fig.
In addition, the total numbers of individuals tended to be different (Friedman chi-squared = 29.98, p < 0.001): they were low in July and August, compared to values observed in June and September (Fig.
This study identified at least 11 species of earthworms living within levees on Sado Island. Previously, only seven species (Amynthas divergens, A. hupeiensis, Metaphire acincta, Aporrectodea caliginosa, E. japonica, Helodrilus hachiojii and Drawida hattamimizu) had been recorded at rice paddy levees in Japan (
Species diversity and evenness tended to be low at the rice paddy levees; only two species, A. corticis and E. japonica, were dominant. E. japonica is present in most ecosystems in Japan, including mountainous forests and grasslands (
Levee grasslands may also be characterised by relatively-high earthworm densities. For example, previous comprehensive studies conducted in pastures and meadows in Hokkaido, northern Japan, recorded 35.5–200.4 individuals and 14.9–49.7 g/m2 biomass (
However, in the present study, we observed that earthworm densities differed amongst regions. In particular, densities were high at the levees without adjacent forest, compared to levees with adjacent forests. The situation of farmland consolidation and characteristics in soil properties (Soil pH, C, N and C:N ratio) is unlikely to differ between these two types of levees (Table
We also observed that epigeic species were rarely found at the levee grasslands in this study. Epigeic species live in the litter layer and feed on litter (
Monthly changes in earthworm densities occurred in the topsoil of the levees. The changes are likely linked to the life cycles of some species. For example, for some endogeic species of Megascolecidae, cocoons hatch from April to September; thus, juveniles and adults appear throughout the year (
We greatly appreciate the farmers who allowed us to collect earthworms from their paddy levees. We also thank Fujio Hyodo for his analysis of soil C and N concentrations and C:N ratios, Yukiyoshi Kamihira and Satoshi Kaneda for their helpful comments on earthworm density in grasslands and agricultural lands and Hisashi Nagata for his valuable comments on the crested ibis. This research was supported by the Environment Research and Technology Development Fund (4-1606) of the Ministry of the Environment, Japan.