Abstract
Aquatic oligochaetes are important fauna in paddy fields because they suppress annual weeds and enhance
nutrient cycling. However, further investigation is needed into the use of aquatic oligochaetes in rice production. Abundance surveys of aquatic oligochaetes in paddy soils have predominantly been conducted by time- and labor-intensive hand-sorting. A wet funnel apparatus is useful for efficiently extracting organisms such as nematodes and enchytraeids from soil. In this study, I first compared the extraction efficiency and counting speed of oligochaetes between handsorting and wet funnel apparatus application. While soil is generally used for the latter, I instead used soil residue separated from the soil. Second, extraction efficiency was compared between two major wet funnel apparatus methods, the Baermann and O’Connor approaches. Mustard powder with the active agent of allyl isothiocyanate was used to extract oligochaetes from the soil. The effectiveness of the addition of this agent, likely repellent for aquatic oligochaetes, in the Baermann apparatus was confirmed in terms of extraction efficiency in the third experiment. Lastly, the feasible storage duration of oligochaetes at three different temperatures after extraction was determined. The Baermann apparatus could effectively extract approximately 90% of oligochaetes and increased the counting speed. Compared with the Baermann apparatus, the O’Connor apparatus slightly increased extraction efficiency in Gleyic Fluvisols and Hydragric Anthrosols; however, adding mustard (0.01 g L－1) did not affect efficiency in this case. Extracted oligochaetes were stored in tap water at 6°C, 10°C, and 15°C. Oligochaete survival rate decreased to approximately 90% after four days, but then remained constant for 2 weeks. This study demonstrates that the wet funnel apparatus technique is a powerful tool for abundance surveys of aquatic oligochaetes in paddy fields.
