Copepoda and Cladocera in the Uryu-numa moor, Hokkaido

Abstract

The Uryu-numa moor, 900 m above sea level, is situated at the northwest suburbs of Uryu-mura in Hokkaido. The moor, about 2 km from east to west and 1 km from south to north, is surrounded by four high mountains. In the moor, there are a great number of ponds in various forms and sizes. Most of them are round in form, with diameters 1-50 m and water depths 1-4 m.
Water temperature, pH and the aquatic plants of the ponds surveyed are shown in the Table 1.
Eighteen species of crustacean plankton, three copepods and fifteen cladocerans were found inhabiting the ponds in the moor. These species are listed in the Table 2.
In the crustacean plankton, Acanthodiaptomus pacificus (BURCKHARDT), Diaphanosoma brachyurum (LIÉVIN), Daphnia longispina (O. F. MÜLLER) and Chydorus sphaericus (O. F. MÜLLER) occurred most widely. The dominant species was Acanthodiaptomus pacificus, followed by Daphnia longispina and Diaphanosoma brachyurum. Holopedium gibberum ZADDACH was found only in a few ponds in which it was the dominant species.
Drepanothrix dentata (EUREN) and Eurycercus glacialis LILLJEBORG were found by this survey for the first time in Hokkaido. Eurycercus glacialis has been kown to be an arctic species, the southern limit of its distribution having been reported to be the Island of Paramushir of the North Kuriles (UENO, 1933, 1938). Therefore, its occurrence in Uryu-numa, Hokkaido, is noticeable from the zoogeographical standpoint.