Distribution of Intertidal Macrobenthos in 1993 around Hatakejima Island, Central Japan, Compared with 1969 and 1983-84

Abstract

The intertidal biota of Hatakejima Island in Tanabe Bay, central Japan, was investigated in May, 1993. A survey of selected animal species around the entire coast of the island revealed different patterns of distribution in relation to wave exposure and substratum type. Comparison between the present data and those obtained in 1983 shows that several species obviously extended or contracted their distribution ranges around the island. In the survey of a selected area on the south coast, 173 macro-benthic species including 112 animal and 61 plant species were recorded. Mollusca and Crustacea were dominant among the animals, and Rhodophyta among the plants, in terms of number of species. Comparison between the present data and those obtained in 1969 and 1984 on the south coast reveals that the total number of animal species and their distribution ranges decreased from 1969 to 1984 and increased from 1984 to 1993. The species with a southern geographical distribution (<35°N) contracted and the indicator species of eutrophic water expanded their ranges from 1969 to 1984, and the reverse changes occurred from 1984 to 1993. Photographs show drastic changes in the shore scene: obvious sedimentation in 1984 and alternation of the dominant sessile bivalves between 1969 and 1993. The fluctuation in abundance of the species with a southern geographical distribution paralleled changes in the water temperature, and the fluctuation in abundance of the indicator species of eutrophic water paralleled changes in the indices of nutrient level. An influence of these environmental factors on the faunal changes of the intertidal Hatakejima Island during the last 25 years is inferred.