Distributins of some interstitial harpacticoid copepods in an intertidal sediment (Preliminary report)

Abstract

Three species of interstitial harpacticoid copepod (Phyllopodopsyllus punctatus, P. setouchiensis and Oniscopsis inabai) are characteristic inhabitants at the upper shore of Mukaishima Island in the Inland Sea of Japan. These species occurred jointly in the narrow zone, but their center of distributions were delicately separated. The depth distribution of each species in the sediment and their seasonal and diurnal migrations were investigated. Each species had characteristic depth-distribution pattern, and their relative positions were unchanged throughout most of the year irrespective of vertical seasonal mi.gration. P. punctatus, dweller of the shallow layer, made clear seasonal shift to the deeper layer in winter, but the tendency was not so obvious in other two deeper zone dwellers. Two Phyllopodopsyllus species made slight vertical movement during one daily tidal cycle, moved toward surface at ebb tide and toward deeper at flood tide. Some physical properties of the sediment were measured, but none of them positively correlated with species specific distribution patterns. Positive evidence of interspecific competition was not observed. To elucidate difference of species specific distribution by biological nature of the sediment, a series of choice experiments was carried out. Each harpacticoid species showed positive preference to the sand of the depth in which the species highly populated. It is suggested that the species specific preference to the organic film on the surface of sand grains may be one of the factors inducing microhabitat segregation within the sand-dwelling copepod community.