Secondary production and trophic basis of sinopotamon teritisum in Heizhuchong Stream, Hanjiang Catchment

Abstract

Macrozoobenthos community plays an important role in material cycle and energy flow in riverine ecosystem. During the period of June, 2003 to June 2004, an investigation on the life cycle and production of the dominant species of macrozoobenthos community in a second-order river of Hanjiang River Basin was carried out. From the upper to the lower reach of Heizhuchong stream, we chose six types of habitats to collect quantitative samples. Station 1 (S1) lied in the middle of the stream with big round rocks in the upper reach, station 2 (S2) was in the inner part of a weir with cobble substratum, station 3 (S3) in the middle of a peacefully flowing section with gravel-sand bottom, station 4 (S4) at the side of the riparian with aquatic macrophytes and snags, station 5 (S5) in the middle of the riffle, station 6 (S6) at the lower reach with a sewage outlet ca 100 meters uppstream. At each station, four quantitative samples were taken with a 167μm D-frame kick net or a Surber net, and the samples were sieved with a 167μm net, sorted in a porcelain dish with naked eye. The specimens were kept in 10% formalin for later processing. The life cycle of the S. teritisum Dai et al. population was analysed by the monthly size-class frequency distribution, the cohort and annual production were estimated by size frequency method. The results showed that S. teritisum completed one generation for nearly 4 years, the reproduction mainly occurred in from middle August to middle October, and most of the senescent individuals died in February. The abundance of the population varied greatly during the year, probably due to the relatively smaller sampling area compared with the strong activity of motion of S. teritisum. Whereas, the variation of the biomass followed the same pattern of the abundance. The a-bundance attained its peak in September with 35 ind/m2, and biomass reached its highest level in June at 41. 7 g/ m2. The estimated cohort production and cohort P/B ratio by size-frequency method were 605.2g/(m2·a) (wet wt) and 5. 5, respectively; the annual production and P/B ratio were 151. 3g/(m2·a) ( wet wt) and 1.4. The reason why the annual production of the animal in Heizhuchong Stream was the relatively higher was because of its high density. By analyzing its stomach content, the proportions of amorphous detritus, caridina, aquatic insect larvae, gastropods and vascular tissues were 45.4% , 10.9% , 35.6% , 5.7% , 8. 1% . Therefore, the contribution rates of the above types of food to production were 10.84% , 18.21% , 59.49% , 9.52% , and 1.94% , respectively.