Distribution of Macrobenthic Animals in the Rivers and the Harbor Area of Osaka City

Abstract

To clarify the effects of organic pollution on the macrobenthos, quantitative samples were obtained from the rivers and the harbor area in Osaka City between August 1984 and April 1987. The rivers were shown to be a polysaprobic zone by the predominance of oligochaetes. The densities and biomasses in the rivers were low, excepting in Neya River, where an extremely dense population of a tubificid oligochaete was found throughout the year. In the mouths of the rivers, i. e., the innermost part of the harbor, animals were scarce from spring to autumn owing to severe oxygen deficiency. In winter, however, Capitella capitata and several euryhaline species appeared in abundance by the rapid increment of the population. Then, clear faunal boundary was found to lie between the innermost part of the harbor and the area around the mouth of the horbor where Paraprionospio sp. (form A), Lumbrineris longifolia, Sigambra sp. and season-specific species such as Euchone sp. and Theora fragilis were distributed. Comparison of the dominant species in the present study with those in the previous studies suggests the change of environment during the past 30 years.