Geographical distribution and habitats of a spring-dwelling amphipod, Jesogammarus fluvialis Morino (Amphipoda)

Abstract

Jesogmmarus fluvialis Morino is one of spring-dwelling amphipods in central Japan. I collected this amphipod from 1986 to 2006 to know the geographical distribution and the environmental features of its habitats. The wide-area survey indicated that this species was distributed apart the two spring zones around the Suzuka Mountains and Mt. Fuji, and that the high density of the amphipod was restricted near the headspring. Most of the habitats were springbrooks with the following features: (1) water temperature ranging from 10 to 17°C, (2) sand and/or gravel on the bottom, (3) on flat ground, (4) exposure to the sun (i. e. open field), and (5) luxuriant growth of emerged and/or submerged plants. In such springbrooks, the amphipods gathered and attached on water plants with asselids and some insects. Survey of the microdistribution suggested that the amphipod appeared to aggregate into a dense assemblage of water plants, and that the inhabitance was impeded by accumulation of sludge and predators such as shrimps and fishes.