STUDIES ON ASSEMBLAGE CHARACTERISTICS OF MACROZOOBENTHOS IN THE WEST RIVER

Rivers have many service functions such as water supply, food production, sightseeing, shipping and so on, hence playing an important role in people's living and agricultural production. During the last decades, intensive human activities have been threatening river ecosystem. Macrozoobenthos are important components of river ecosystems, playing an important role in trophic dynamics by cycling nutrients and providing food for higher trophic levels such as fish and birds, and they are often considered as good indicators of long-term changes in environments due to their confinement to the bottom, long life cycles and limited abilities of movement. A better understanding of macrozoobenthic assemblages is of great significance to river conservation and management. For shipping, spur dikes have been built along river bank to increase water depth, thus, river ecosystems face the threat of reduced service functions. To conserve and manage the West River, field investigations of macrozoobenthos were conducted in November 2009 (at low water level) and May 2010 (at high water level). Altogether 70 taxa of macrozoobenthos belonging to 30 families and 59 genera were identified. Among them were 16 annelids, 21 mollusks, 32 arthropods and 1 miscellaneous animal. The average density and biomass of total macrozoobenthos were 140 ind/m2 and 0.23 g dry weight/m2, respectively. Macrozoobenthic density peaked in the cobbles, while biomass reached the maximum in the bedrock. Detrended Correspondence Analysis (DCA) revealed that substrate played an important role in structuring macrozoobenthic assemblages. The higher substrate stability was more favorable to survival of benthic animals. Macrozoobenthic assemblages in soft sediment were characterized by dominance of collector-gatherers (mainly Tubificidae and Chironominae), while macrozoobenthos in stone substrates were dominated by scrapers (e.g. Semisulcospira spp.) or collector- filterers (e.g. Limnoperna lacustris). In recent years, channel regulation projects have led to reduction of habitat quality and habitat loss, which will have a negative impact on survival of benthic animals.