Study On The Community Ecology Of Macrobenthic Fauna In The Wetland Of The Zhanjiang Mangrove Nature Reserve

Mangrove vegetation plays an important role in maintaining its environmental complexity and affecting the diversity and distribution of animals related to mangrove's ecological system. Destruction of mangrove would reduce the diversity of macrobenthic fauna community. At the same time, macrobenthic fauna constructed an important part in the mangrove ecological system: they were both the consumer and transporter in the energy flow and the materials circulation in the ecological system. By activities such as ingesting food, digging cave and setting up tube, macrobenthic fauna interacted with their surrounding environment. So the community structure of them had become a significant index for us to recognize mangrove's environmental characteristics and to predict mangrove environmental quality. It had the potential designation function to biologically/ecologically recognize the environmental changes in the natural and artificial mangrove.Macrobenthic fauna communities in the wetland at the Gaoqiao, Qishui, Fucheng, Hean, Wuli town in the Zhanjiang Mangrove Nature Reserve located along coastal areas of the Leizhou Peninsula, Guangdong, China, were investigated. The aspects such as the spatial zonation of macrobenthic fauna affected by mangrove community were studied.The main research results were as follows:1. The spatial zonation of macrobenthic fauna was studied with two transects vertical to the shoreline. Along the first transect near Deyao village, three faunal zones of the mangrove swamp could be divided from the high to low tide part: Assiminea lutea–Uca arcuata–Paracleistostoma crassipilum zone, Cleistostoma dilatatum–Macrophthalmus erato–Littoraria melanostoma zone, and Paracleistostoma depressum–Cerithidae cingulata zone. Molluscs and crustacean exhibited highest individual density in this transect. Molluscs also mainly influenced the dynamics of community biomass, as well as the species diversity index. In the second transect near Hongzhai village, four faunal zones could be determined in this section: Littoraria melanostoma–Pseudoringicula sinensis–Ceratonereis burmensis zone, Assiminea lutea–Cleistostoma dilatatum zone, Upogebia sp.–Paracleistostoma depressum zone, and Metaplax sheni–Cerithidae cingulata zone. The crustacean showed highest individual density in this transect. Similar to the Deyao transect, dynamics of community biomass and the species diversity index of the Hongzhai transect were mainly influenced by molluscs. By hierarchical clustering and non-metric multi-dimensional scaling, the macrobenthic fauna communities could be divided into 3 and 4 groups in the Deyao and Hongzhai transect respectively. These groups corresponded to the different vegetation types of the mangrove swamp. In summary, our observations indicate that the spatial zonation of the macrobenthic fauna was mainly affected by characteristics of the mangrove community, sediment characteristics and the tidal line.2. The characteristics of macrobenthic fauna communities in mangrove's three successional stages (Avicennia marina+ Aegiceras corniculatum stage, Kandelia candel+ Aegiceras corniculatum stage, and Bruguiera gymnorrhizai+ Aegiceras corniculatum stage) were studied. The results showed that of these successional stages, the number of species, biomass, density, Pielou's evenness index, richness index and Shannon-Wiener index of the macrobenthic fauna communities were the highest and dominance index was the lowest at the Avicennia marina+ Aegiceras corniculatum stage. At Kandelia candel+ Aegiceras corniculatum stage, the number of species, especially those of the life forms of infaunal and adhering, reduced heavily. The biomass reduced accordingly and the density dropped to the lowest of the three successional stages. Shannon-Wiener index decreased at this stage. At Bruguiera gymnorrhiza+ Aegiceras corniculatumi stage, the number of species, especially those of the life forms of infaunal and caving, continued to decrease. Here, the density increased and the biomass became the lowest of the three successional stages. The dominant life forms at Avicennia marina+ Aegiceras corniculatum stage were infaunal and caving, while those at Kandelia candel+ Aegiceras corniculatum stage and the Bruguiera gymnorrhiza+ Aegiceras corniculatum stage were caving. The ratio of the GS/GSB of macrobenthic fauna in these three mangrove communities was 0.48, 0.38, 0.80, respectively. The community structures at the same successional stage of mangroves were all quite similar and those at Bruguiera gymnorrhiza+ Aegiceras corniculatum stage exhibited even more similarities. However, there were obvious differences among community structures at the three successional stages, which showed that the mangrove could influence the macrobenthic fauna community obviously by direct or indirect reconstruction of the environment, i.e. the change in the chemical property of the sediments and the light level in the forest, the provision of different food. Likewise, the findings from the analysis of macrobenthic fauna life forms also lend proof to the role of the mangrove and accordingly demonstrated the macrobenthic fauna adaptation capability to the specific habitats at different stages.3. The characteristics of macrobenthic fauna communities in three Sonneratia aoetala stands planted in the year 2000, 1997 and 1995 respectively were studied. The results showed that the characteristics of macrobenthic fauna communities have taken place obvious variety along with Sonneratia aoetala plantations's progress of the ecosystem instauration. The number of species, Shannon-Wiener index and richness index of macrobenthic fauna communities were significantly negative related with the development condition of the Sonneratia aoetala plantations.4. The structure and niche of the mollusca community were analyzed. The results showed that the main factor affecting the mollusks density distribution was the mangrove community but not the seasonal variation. Adopting the mollusk density data of quantitative sampling in Zhanjiang Mangrove Nature Reserves, niche breadth and niche overlap of the mollusk were measured with Shannon-Wiener index and the Pianka formula. The hierarchical cluster dendrogram and MDS ordinal configuration of mollusk were also used for further analysis. Comparing with actual quantitative sampling, the results reveal that the analysis method using mangrove and season to decide the number of the environment resources sites agrees with real situation.5. ABC curve of macrobenthic fauna communities was used to assess the environment quantity of mangrove wetland. The results indicated that the abundance curves were all above the biomass curves at these investigated sites of Gaoqiao, Qishui, Fucheng, Hean, Wuli town. This means that the study area had been plluted. Concents of heavy metals, polycyclic aromatic hydrocarbons (PAHs), dichlorodiphenyltrichloroethanes (DDTs) and hexachlorcyclohexanes (HCHs) in surface sediments from the five mangrove investigated sites were monitored. The results indicated that the average concents of As from Gaoqiao, Qishui, Fucheng, Wuli; Cr, Cu from Wuli; Ni from Gaoqiao, Qishuic, Hean; and Hg from Fucheng were higher than ERL. However, Ni levels in surface sediments of mangrove swamps from Fucheng and Wuli were higher than ERM. Concents of DDTs in sediment from Qishui, Fucheng, Hean were all higher than ERL. Concents of DDTs in sediment from Wuli were higher than ERM. Being in accordance with the results of chemistry monitor, the ABC curve of macrobenthic fauna communities can be used to assess the environment quantity of mangrove wetland.6. The richness, biomass, secondary productivity and P/B value of the macrobenthic fauna were studied with Brey's empirical formula. The results showed that in proper order, the richness, the biomass, the secondary productivity of the macrobenthic fauna at the five mangrove investigated sites were Qishui > Hean > Fucheng > Gaoqiao > Wuli, while the P/B value of them was Gaoqiao > Wuli > Qishui > Fucheng > Hean. The richness, the biomass, the secondary productivity and the P/B value of them in Zhanjiang Mangrove Nature Reserve were 226 ind/m2, 13.55 g (AFDW)/m2, 11.25 g(AFDW)/(m2·a) and 0.96 respectively. The sediment characteristics were different among different mangrove communities. And the difference of the environment factors such as the concents of organic matter, sand and slit affected the the secondary productivity of the macrobenthic fauna in the mangrove wetland.