中海・宍道湖に生息するトンボ類とその塩分耐性

Survival of Odonata nymphs was experimentally compared in waters with different salinities. Nymphs were monthly collected from Shinjiko and Nakaumi lagoons (at two issues), near Matsue. Survival period varied evidently from season to season but slightly by sample provenance. A dominant species in a community, Cercion hieroglyphicum, tolerated 2.0% salinity for more than 21 days in November, while in July survived only for 5 days. Another dominant, Calopteryx atrata, was more susceptible to the salinity; died within 3 days in May. The whole community including C.atrata was observed to be absent during summer season, presumably due to accidental invasion(s) of brackish water. Seasonal variation in salinity of the lagoons should thus be signifi-cant to the restriction of the habitat of these Odonata species.
Key words: habitat, lagoon, Odonata, salinity tolerance, seasonal variation