Abstract: ased on the survey from July 1985 to June 1986,this paper discusses the distribution of biomassand its density and the composition of species of benthic animals in Yantai inshores. It revealsthat benthic animals have lower biomass, higher density and more complicated species composi-tion with less obvious seasonal variation. Polychaeta has the largest biomass and the highest den-sity. being the dominant species in survey area. The density and biomass of benthic animals areevenly distributed in all survey stations except higher in No.8 and lower in No.9 and No.10 sur-vey ones.The highest biomass is determined in spring,and the lowest in summer,and the re-vease is its density. The reason of lower biomass in No.9 and No.10 survey stations is also ana-lyzed.

Key words: diatoms, diatom indices, river health, bio-assessment.