Fluctuation patterns of macrobenthic fauna during the stratification period in the eastern part of Hiuchi-Nada, Seto Inland sea.

Abstract

The spatial distribution patterns of macrobenthic fauna and their temporal fluctuation were investigated in the eastern part of Hiuchi-nada during the stratification period (July-September) in 1982. To analyse re-cruitment patterns of benthos in the hypoxic environment, weekly sampling was carried out at the station of the deeper area in the same season. The dominant macrofauna in the hypoxic stations consists of two categories with different types of life cycles and reproductive patterns. One is represented by Prionospio ehiersi and Paraprionospio sp. type B which have annual life cycle with single reproductive season. The other group which includes Theora fragilis, Prionospio cirrifera, Cossura coasta and Sigambra tentaculata are short-lived species, considerable number of juveniles recruited several times during the stratification period. However, most of the juveniles found at hypoxic stations died off immediately after settlement and never grown up to adult size.