The effects of invasive cordgrass Spartina alterniflora on burrowing crab communities in the salt marshes of the Yangtze River Estuary, China, were studied. Crab abundance, distribution and diets were compared in native Phragmites australis and invasive S. alterniflora stands. Spartinainvaded stands had 42% higher crab density than did native P. australis stands, largely because 2 dominant grapsoid crabs, Helice tientsinensis and Chiromantes dehaani, thrived in S. alterniflora stands. Sediment grain size, water content and vegetation stem height were the main factors correlated with crab distributions. Crab diet analyses revealed that crab stomach fullness was similar in stands of different plant species, indicating that in Spartina-invaded stands crabs can find compatible food quantity as in native plant stands. Both H. tientsinensis and C. dehaani from S. alterniflora stands had significantly higher δ 13 C values than those from P. australis stands, suggesting that the crabs consumed S. alterniflora in the invasive marshes. This non-selective feeding may be driving the success of H. tientsinensis and C. dehaani in invasive Spartina stands.

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In many salt marsh ecosystems, crabs are the most prominent members of the macrobenthic community, influencing material cycling and energy flow. Studies on population dynamics and secondary production are important for quantitative evaluation of the ecological function of crabs; however, few studies have been conducted in salt marsh ecosystems. In this study, we investigated the secondary production and population dynamics of two Thoracotremata species in an Asian salt marsh. A year-round sampling on a monthly basis in the Dongtan salt marshes of the Yangtze River estuary yielded 12 species of crabs belonging to 7 families and 10 genera. The dominant crabs were Chiromantes dehaani (67.57%) and Hélice tientsinensis (17.28%). The overall size frequency distribution was bimodal for C. dehaani and unimodal for H. tientsinensis. The estimated annual production of C. dehaani and H. tientsinensis was 43.981 g and 4.247 g ash-free dry weight (AFDM) m~^ year" ', respectively. The annual P/B ratio was 1.22 for C. dehaani and 0.75 for H. tientsinensis. In total, the annual secondary production of all crabs at the Dongtan salt marshes was estimated to be approximately 49.405 g AFDM m"^ year" '. The consumption of vascular plants by C. dehaani and H. denLnnensis was 480.831 and 42.640 g AFDM m"^ year"'. About 20.4% of plant primary production was ingested by these two herbivorous crabs. The production of C. dehaani was high compared with those reported from other coastal wetland ecosystems. This suggests that the ecological functions of C. dehaani at the Yangtze River estuary salt marshes need more quantitative studies to be fully described. RÉSUMÉDans de nombreux écosystèmes lagunaires, les crabes sont les représentants les plus dominants de la communauté macro benthique, influençant le cycle de matériaux et le flux d'énergie. Les études en dynamique des populations et production secondaire sont importantes afin de quantifier la fonction écologique des crabes ; cependant, peu d'études ont porté sur les écosystèmes lagunaires. Dans cette étude nous avons investigué la production secondaire et la dynamique des populations de deux espèces Thoracotremata dans des lagunes asiatiques. Des échantillonnages mensuels pendant toute une année dans les lagunes de Dongtan de l'estuaire de la rivière Yangtze ont fourni 12 espèces de ')

Dendritic tidal creek networks are important habitats for sustaining biodiversity and ecosystem functioning in salt marsh wetlands. To evaluate the importance of creek heterogeneity in supporting benthic secondary production, we assess the spatial distribution and secondary production of a representative polychaete species (Dentinephtys glabra) in creek networks along a stream-order gradient in a Yangtze River estuarine marsh. Density, biomass, and secondary production of polychaetes were found to be highest in intermediate order creeks. In high order (3rd and 4th) creeks, the density and biomass of D. glabra were higher in creek edge sites than in creek bottom sites, whereas the reverse was true for low order (1st and 2nd) creeks. Secondary production was highest in 2nd order creeks (559.7 mg AFDM m−2 year−1) and was ca. 2 folds higher than in 1st and 4th order creeks. Top fitting AIC models indicated that the secondary production of D. glabra was mainly associated with geomorphological characters including cross-sectional area and bank slope. This suggests that hydrodynamic forces are essential factors influencing secondary production of macrobenthos in salt marshes. This study emphasizes the importance of microhabitat variability when evaluating secondary production and ecosystem functions.