Population dynamics and production of Neanthes japonica (Izuka) in a shrimp pond

During late February to mid-March, 1991, when mature N. japonica swarmed in the sea surface off Jimo County, Qingdao, seawater containing numerous early embryos was pumped into a nearby 2.7 ha. muddysand shrimp pond, where the embryos continued to develop. 800000 Penaeus chinensis seedlings were introduced into the pond on May 30, 1991. Monthly benthic samplings were carried out to determine the population dynamics and production of N. japonica in this atypical environment. The density of N. japonica varied from 0 to 20 400 ind./m². The predation of P. chinensis was considered to be responsible for the mass mortality of N. japonica in June through July, when the worms were 2.2-3.3cm in length and lived in the top 2-4cm sediment. From August to September of 1991, the hottest period in the site, there was no substantial mortality of N. japonica as reported in earlier literature. This was explained by the deeper burrowing of the worms that protected them from predation by shrimps. Monthly biomass ranged from 45.2 to 385.3 g/m², with a mean of 187.7 g/m². Production of May. 1991 through March, 1992 was 1071.4 g/m², with a P/B ratio of 5.7.