THE IMPACT OF OVERSTOCKING OF MITTEN CRAB, ERIOCHEIR SINENSIS, ON LACUSTRINE ZOOBENTHIC COMMUNITY

To examine the impact of mitten crabs(Eriocheir sinensis) on zoobenthic community, a comparative study was conducted along Changjiang River in 1998-1999 between crab-overstocking-lake, Huanghu Lake, and the reference waters, viz. unstocked vicinity of Huanghu Lake, natural-fishing-lake, Longganhu Lake, and fish-stocking-lake, Niushanhu Lake. The parameters include species composition, body size, standing crop, functional feeding group and production. The results showed that the species diversity of Huanghu was substantially lower than that of the references. Due to the extinction of submerged macrophytes, small scrappers on the plants were greatly decreased in Huanghu, and subsequently, big gastropods, Bellamya, feeding on the bottom, became dominant. Under the stocking density of about 1kg穐m-2 of crab larvae or juveniles, zoobenthic density and production were reduced by more than 60%. Inferentially, zoobenthos are affected by mitten crabs in two ways, i.e. direct feeding on benthos, and indirect effect through damage of submerged macrophytes. Considering that the method of capacity estimation of mitten crabs has not yet been established, the authors are of the opinion that mitten crabs and planktonivorous fishes should be in rotation of stocking for the purpose of sustainable utilization of natural resources.