Distribution of Hoplocarida and Decapoda shrimps in Oujiang estuary,East China Sea

Based on the data of two oceanographic surveys in the Oujiang Estuary in June and September 2007,this study investigated distributions of Hoplocarida and Decapoda shrimp(simplely called"shrimp")resource density, species composition,richness and diversity(H′)and the effects of some impact factors such as dominant species, background of water masses as well as hydrological features on these distributions.Results showed that 17 shrimp species were identified.Among them Oratosquilla oratoria and Parapenaeopsis hardwickii were key species in June, while O.oratoria was the key species in September.Weight density was 41.14 kg/km2 and individual density was 18.41×10 3 ind/km 2 in Jun,and 32.36 kg/km 2 and 10.66×10 3 ind/km 2 in September respectively.Both weight and individual distribution showed the same tendency that the densities in the east area were higher than those in the west area,and the densities in the south area were higher than those in the north area.This is the reason why shrimp density was positively related with water depth.Two dominant species and their high richness made even distribution of total shrimp weight and individual in different species,and finally formed high H′values in June.Different from June,O.oratoria,as a single dominant species in weight,aggregated in outer water and formed single dominant species low H′values in outer waters in September.The shrimp population continually stay from June to September at outer waters of investigated areas,especially in south east where the water was affected by Taiwan current.The low shrimp density in north waters of the Oujiang estuary was caused by the Oujiang dilute water from the estuary. Seasonal and regional Oujiang dilute water was critical hydrological factors affecting shrimp species and diversity in this area.