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To assess the effectiveness of different fisheries management strategies in freshwater reservoirs in China, we use hydroacoustic techniques to quantify the density, biomass, size, and patterns in distribution of fishes in Wanyao (WY), Laohutan (LHT), and Qiaodun (QD) reservoirs (Zhejiang Province), each of which has been managed differently. Significant differences in density, biomass and size distribution are reported among these reservoirs. In the overfished WY, fish density and biomass are lower than that in LHT (P 48 cm) were caught and the smaller ones were left in the reservoir, proportionally more mid-sized fish (˜11–48 cm, 84.63%) are present than smaller or larger fish. Our research improves the understanding of the relationships between fisheries management strategies and the density, size and biomass of fishes in reservoirs.We demonstrate that fisheries management strategies play an important role in maintenance of fish resources in reservoirs, and that hydroacoustics techniques can be successfully used to quantify fish density and size distributions.

Macrozooplankton may play important roles in influencing nutrient exchange between salt marsh and nearby estuarine ecosystems through predator-prey interactions and their transport by tidal flows. In this study, macrozooplankton transport through year-round monthly sampling was investigated in a salt marsh creek of the Yangtze River estuary. Twenty-one orders of macrozooplankton were captured. Calanoida and Decapoda were dominant and numerically comprised 59.59% and 37.59% respectively of the total captured macrozooplankton throughout the year. Decapoda mainly occurred in April, May and June. In other months, the Calanoida contributed over 90% of the total individuals. The annual Ferrari index ( I ) for total individual number of macrozooplankton was 0.27, which generally supports the viewpoint that salt marshes are sources of zooplankton. The salt marsh was mainly a source for decapods and mysids, possibly because of larval release in their breeding seasons. The marsh was also a source for amphipods, probably because some benthic forms became transient planktonic forms during tidal water flushing. Copepods and fish larvae exhibited net import into the salt marsh, which may result from predation from salt marsh settlers or retention in the salt marsh. Monthly Ferrari index ( I ) estimations revealed that the role of the salt marsh as a sink or source of macrozooplankton was time-dependent, which is related to the life history of animals. This study showed that whether the salt marsh zooplankton act as energy importers or exporters is group/taxa-dependent and time-dependent.

The response of deposit-feeding animals to plant invasions is still unclear, because their food sources are often difficult to identify. We examined the effect of the exotic plant species, Spartina alterniflora, on the food source composition of two dominant snail species, Assiminea latericea and Cerithidea largillierti, in the Yangtze River estuary salt marsh using a combination of stable isotope and fatty acid analyses. We collected the snails and their potential food materials (sediment organic matter, particulate organic matter, and plant material) in S. alterniflora and native plant Phragmites australis marshes and then determined the composition of food sources of snails based on fatty acid markers and stable isotope composition. Our results indicated that A. latericea and C. largillierti are deposit feeders grazing on sedimentary particles originating from diatoms, bacteria, and vascular plants. Invasive S. alterniflora did not result in a change in the relative contribution of microalgae, bacteria, and vascular plants to the food source of the snails. Spartina alterniflora was confirmed to be assimilated by both snail species. The higher assimilation of S. alterniflora by A. latericea compared with C. largillierti is probably related to the greater ability of A. latericea to assimilate plant materials from detritus, as evidenced by fatty acid composition. Overall, S. alterniflora can be incorporated into the food web of the estuarine salt marsh by the dominant snail species with generalist-feeding habits.

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 Helice 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−2 year−1, 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−2 year−1. The consumption of vascular plants 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. 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.

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. Spartina- invaded 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 corre- lated 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 compati- ble 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.

Zooplankton are important grazers of primary production within intertidal marshes and are the optimal prey of higher trophic consumers; however, the patterns of their spatial distribution in marsh creeks are rarely reported. The zooplankton in the intertidal creeks with different salinities at Dongtan marshes of the Yangtze River Estuary was surveyed. The mean zooplankton densities in the intertidal creeks were 53,638 ind. m −3 in April and 132,916 ind. m −3 in July, respectively, which were as high as in the near-shore subtidal waters of the Yangtze River Estuary. This high abundance implied the important roles of zooplankton in the matter flux between marshes and near-shore waters through complex intertidal creek systems. Zooplankton total densities changed significantly from northern to southern creeks. ANOSIM and CCA analyses revealed that the zooplankton community structure were significantly different among the northern, eastern and southern creeks, and between two sampling seasons. Salinity accounted for most of the spatial variation of zooplankton community, whereas water temperature, chlorophyll a concentration, and pH were the main reasons of the temporal variation observed. Copepods were the most abundant zooplankton group. A total of 24 copepod species, belonging to 15 families and 20 genera, were recorded. Planktonic copepods preferred the northern and eastern creeks, with higher densities in July than in April, while benthic copepods predominated only in the northern creeks in April. Since the role of benthic and planktonic copepods may differ in transporting nutrients in the intertidal creeks, it is suggested that the variations in their distribution may influence the ecological functions of zooplankton in the estuarine matter fluxes both spatially and temporally.

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.