Ecological Studies Of Macrozooplankton Communities In Salt Marsh Creeks Of The Yangtze River Estuary

It is a general accepted view that the primary productions of saltmarshes could delivered to the adjacent estuary and offshore ecosystem through tide dynamic an biological migration and might become main energy resource maintaining the secondary productivity of the food web in these ecosystems. At present, a lot of previous studies have confirmed that the most biomass of zooplankton was contributed by macrozooplankton. Also many studies have revealed the intermediate linking role of macrozooplankton between primary producers and higher level consumers. Therefore, learning the community structure of salt marsh macrozooplanktons and the trophic connection between them and other biomes is very important for us to understanding the wetland ecosystem function and the linking of material and energy with adjacent water ecosystem. In this study, saltmarshes in the Chongming Island and Jiuduansha Islands of the Yangtze River estuary are selected as study sites. We estimated the input and output of the macrozooplankton in the salt marsh creeks. Meanwhile, the technology of stable isotopic analysis and stomach content analysis were used to reveal the predator and prey relationships between macrozooplankton and others organisms. Also the role of macrozooplankton in the material connection and exchange between the salt marsh and the estuarine ecosystem was preliminarily explored. The main results are listed as follows:1) To understand the composition, diversity and the spatial and temporal pattern of macrozooplankton in saltmarshes of the Yangtze River estuary, using fyke-net, I researched the community structures of macrozooplankton in Xiaonangang creek which had higher salinity and turbidity and Tuanjiesha creek which had lower salinity and turbidity, of the Chongming Dongtan salt marsh. During the study, a total of 28 taxa belonging to 9 orders and 18 families were found from the salt marsh creeks of the Yangtze River estuary over two seasons. The most numerically abundant taxa were Calanoida, zoea larvae of crabs and Acanthomysis brevirostris, which contributing about 98% of the total abundance. The results of variance analysis showed that macrozooplankton distribution has obvious seasonal pattern and spatial difference. Calanoida, zoea larvae of crabs and fish larva mainly occurred in May. However A. brevirostris were found mainly in October. The dominant taxon of Tuanjiesha creek was fish larva. But the dominant taxa of Xiaonangang creek were Calanoida, zoea larvae of crabs and A. brevirostris.2) To access the input and output of the macrozooplankton in the salt marsh wetland, an annual research about macrozooplankton fluxes was carried out monthly using stow net in Jiuduansha saltmarshes from March 2010 to February 2011. The relative flux of macrozooplankton was calculated through the formula of'Ferrari index'(â… ). The calculation result suggested Jiuduansha salt marsh was the resource of macrozooplankton. There is net flux from Jiuduansha salt marsh to adjacent water ecosystem. Zoea larvae of crabs, zoea larvae of Diogenidae, Perioculodes meridichinensis, juvenile of Macrobrachium nipponense, A. brevirostris and Grandifoxus cuspis were the main biological output. Among them, a mass of larvae of salt marsh crabs releasing in breeding season had important significance for the total output. On the contrary, the input of other taxa, e.g. Calanoida, fish larva, Megalopae of Helice tientsinensis, Corophium sinensis and juvenile of Ilyoplax deschampsi, was more than output. I think some of juvenile crabs or megalopae of crabs coming into the salt marsh to finish its adult life cycle. And also the Calanoida and Corophium sinensis might be preyed in the salt marsh.3) To understand the food source of macrozooplankton and the effects of the Spartina alterniflora invasion to its diet, I compared the food source of macrozooplankton collected from creeks lying in the north of Chongming Dongtan salt marsh having S. alterniflora distribution with macrozooplankton capture from creeks lying in the south of Chongming Dongtan salt marsh just having native plant distributing area through stable isotopic analysis technology. The results showed that carbon stable isotope values of POM, particulate organic matter, in the north creeks were significantly higher than in the south creeks. The reason was the invasion of S. alterniflora affected the POM in the creeks. It can be explained that there were POM coming decomposition from S. alterniflora and higher vegetation in the creeks. And the POM might be food resource of macrozooplankton. The carbon stable isotope values of Calanoida, fish larva and juvenile shrimps from the north creeks were significantly higher than that from the south creeks. The result suggested that macrozooplankton feeding POM from salt marsh primary productivity. Moreover macrozooplankton in the north creeks ingested organic matter from Sp. alterniflora. 4) In order to understand the energy basis of crab larvae, which is the dominant macrozooplankton species in salt marsh creeks, we sampled crabs from.S. alterniflora and Phragmites anstralis monoculture patches in autumn and winter of 2007 as well as spring and summer of 2008, and made stomach content analysis of the dominant species. The results indicate that the main components of the stomach content of the dominant species, Helice tientsinensis and Chiromanles dehaani arc plant material. The plant material accounts for 37.64-83.99% and 52.77-84.16% in the food composition of H. tientsinensis and C. dehaani, respectively. S. alterniflora invasion does not alter the feeding characteristics of crabs. Plant material still accounts for the largest proportion in the stomach contents of the two dominant crabs. It indicates that salt marsh crabs play a role in transport organic matters from salt marsh to estuary through the adult crab feeding on the vascular plants in salt marsh and release larvae in breeding season.All the results shows that some salt marsh macrozooplankton could transport the primary productivity of the salt marsh plants (including exotic plant) through feeding and releasing larvae to the estuarine and offshore ecosystem. But also there were part of macrozooplankton taxa having net input from estuary to the salt marsh, thus exogenous organic matter were brought into the salt marsh ecosystem. In summary, macrozooplankton play an important role between the salt marsh and estuary offshore ecosystem material transporting processes through its own activities, as well as other biological food web links...