Secondary Production Of Macrobenthos In Salt Marsh Of The Yangtze River Estuary

Salt marsh is one of the most productive ecosystems in the world. This high level of primary production forms the energy and material base for estuarine ecosystem in the sub-tropical and temperate zone. Macrobenthos constitute the key linkages between primary production and higher trophic levels. Secondary production is essential to reveal the role of animals in the energy flow and material cycle. Intertidal creek in the Jiuduansha Island and vegetations in the Chongming Island are selected as study sites. In this study, we focused on the secondary production and combined with information of ingestion, population dynamics, community structure and spatial heterogeneity to reveal the secondary production of macrobenthos in different orders and positions of creek system, and to quantify the primary production through crab community. Major results were as follows:1) Macrobenthos spatial pattern of fine scale along a creek order gradient (1-4 orders) was investigated in Jiuduansha salt marsh. A total of 37 macrobenthos species were identified, the number of dominant species were Dentinephtys glabra, Notomastus latericeus, Ilyoplax deschampsi and Sinonovacula constricta. Planktophagous group was the dominant group which comprised almost 34.29% macrobenthos taxa and 38.00% total individuals, the density was higher in high order creeks than low order creeks. In edge site, the density of total macrobenthos was higher than in bottom site and detritivorous group was in the majority, whereas diversity lower than in bottom site. The difference of macrobenthos community structure between edge and bottom decreased with the increasing creek order.2) Monthly sampling was taken to investigate the secondary production of dominant macrobenthos species(Dentinephtys glabra). In high order (3rd and 4th) creeks, the density and biomass of D. glabra were higher in creek edge sites than in bottom sites, whereas the reverse was true for low order (1st and 2nd) creeks. Density, biomass, and production of D. glabra were found to be higher in intermediate order creeks. The density and biomass of D. glabra was highest in the 3rd order creeks (332.0 ind m-2,0.297 g AFDM m-2), production was highest in the 2nd order creeks (0.560 g AFDM m-2 year-1) and was ca.2 folds higher than in the 1st and 4th order creeks. Density, biomass, and production were negatively correlated with the percentage of sand and positively correlated with the clay-silt content of sediment.3) Empirical method was used to estimate the secondary production of macrobenthos community in creek network. The biomass (13.35 g AFDM m-2) and secondary production (12.48 g AFDM m-2year-1) of macrobenthos community was significantly higher in the 4th order creek than other order creeks. The secondary production (10.29 g AFDM m-2 year-1) of bivalves was highest in the 4th order creek, however, the secondary production (0.64 g AFDM m-2 year-1) of polychaetes was lowest in 4th order creek. The secondary production of macrobenthos was positively correlated with cross-sectional area (F=14.94, P=0.008). Combining the area of each order creek, we estimated the total production of macrobenthos in Jiuduansha Island creek system was 1.74 × 107 g AFDM year-1.4) Crabs were always shown to be the dominant macrobenthos in the vegetation of salt marsh. The secondary production and ingestion analysis were estimated to evaluate the ecological function of crabs. Crabs captured belong to 7 families,10 genus and 12 species, the number dominant crabs were Chiromantes dehaani (67.57%) and Helice tientsinensis (17.28%). The highest production of C. dehaani was in Scirpus mariqueter, followed by Phragmites australis and was lowest in Spartina alterniflora communities. The highest secondary production of H. tientsinensis was in S. alterniflora communities and the lowest in S. mariqueter communities. The production of C. dehaani and H. tientsinensis was 43.981 and 4.247 g AFDM m-2 year-1. The consumption of vascular plant by C. dehaani and H. tientsinensis was 480.831 and 42.640 g AFDM m-2 year-1. About 20.4% of plant primary production was ingested by these two herbivorous crabs in Chongming Dongtan saltmarsh ecosystem.In summary, the study sites were selected in intertidal creeks and vegetation of salt marsh. Spatial difference of macrobenthos was showed by the secondary production and community structure. The study provides information to accurately evaluate the biological resource in ecosystem, lay the foundation of quantitative food web and energy flow research.