A Preliminary Study On The Structure And Function Of Coral Reef Ecosystem In Daya Bay

Coral reefs are usually located in the waters with poor nutrition,which are known as"tropical rainforests in the ocean"because of their high productivity and biodiversity.Coral reefs provide habitats and suitable living environment for many marine organisms,and provide abundant biological resources,huge economic benefits and important ecological functions for human beings.Daya Bay is a semi closed bay located in the east of the Pearl River Estuary in the north of the South China Sea.In recent years,with the development of surrounding industries,tourism and aquaculture,the marine ecological environment has deteriorated to varying degrees.Coral reefs are the most vulnerable and easily disturbed ecosystem in the ocean.Due to climate change and frequent human activities,coral reefs in Daya Bay are facing the pressure of albinism degradation and serious decline of resources.At present,there is little research on the structure and function of the reef ecosystem in Daya Bay,which is not conducive to the management and protection of the reef.In order to provide basic information for understanding the structure and function of the reef ecosystem and provide scientific basis for the sustainable utilization,protection and management of resources in Daya Bay,a preliminary study on the structure and function of the reef ecosystem in Daya Bay was carried out through the construction of protistan biodiversity,benthos diversity and simple food web.The main results are as follows:?1?In the coral reef and non reef areas of Daya Bay,the main protistan community w as bacillariophyta,followed by Chlorophyta?23.88%?,Cryptophyta?13.41%?,Apicomplexa?10.17%?,Ascomycota?5.67%?,Chytridiomycota?4.98?,Rhodophyta?1.15%?,Cryptomycota?0.95%?,Eukaryota?norank?0.23%?,Picozoa?0.13%?,etc.The richness index,diversity Shanno n index and evenness Pielou index of protozoa were 279±128,4.85±1.06 and 0.60±0.10,res pectively.There were significant differences in the sampling time?P<0.05?but no significant difference was showed between the two groups?P>0.05?.The results of principal analysis s howed that the protistan community was divided into four communities with different season al changes,and the seasonal differences of?diversity were significant?P<0.05?.In the sam e season,there was no significant difference in community composition between the coral re ef and the open sea area?P>0.05?.The topological parameters of the symbiotic network sho wed that the total number of nodes,connectivity,modularity,centrality and degree centrality in the coral reef were lower than those in the open sea.The protistan community structure was limited by the environmental factors such as seawater temperature,p H,salinity and diss olved oxygen,which was consistent with the results measured by mantel method.The results of Pearson correlation analysis showed that the correlation between temperature and protobi odiversity index was the largest.The seasonal succession and spatiotemporal distribution of p rotistan could reflect the obvious seasonal characteristics of subtropical climate,the seasonal fluctuation of coastal water and outer sea water in Daya Bay.Because of the relative lack o f hydrodynamics,waves and nutrients in coral reef area,the symbiotic network of protistan i n open sea area had more complex interaction or niche overlap and stronger stability than t hesein coral reef area.?2?A total of 134 species of benthos had been identified in the coral reef investigation area of Daya Bay.The seasonal variation of benthos species was winter?49 species?>summer?49 species?>spring?48 species?>autumn?39 species?.The seasonal variation of average density was winter(1962.51 ind.·m^-2)>summer(179.38 ind.·m^-2)>autumn(96.98 ind.·m^-2)>spring(76.27 ind.·m^-2).The seasonal variation of average biomass was winter(693.37 g·m^-2)>summer(617.11 g·m^-2)>autumn(314.18 g·m^-2)>spring(107.09 g·m^-2).The average value of species richness index?D?,diversity index?H'?and evenness index?J?were 2.83±0.83,1.85±0.58 and 0.48±0.17 respectively.According to the results of NMDS and cluster analysis,the benthos community in Daya Bay could be divided into four groups.There were significant seasonal differences in benthos biomass,abundance,diversity index and community structure?P<0.05?,which may be closely related to the seasonal changes of nutrients and water environment in Daya Bay.The abundance and density of benthos were much higher than those of the open sea area in Daya Bay,which accorded with the characteristics of coral reef as a tropical rainforest.The results of ABC curve showed that the community structure of macrobenthos was disturbed in winter and autumn,but relatively stable in spring and summer.The low biodiversity index in Daya Bay may be related to human factors such as tourism.Compared with traditional coral reef monitoring methods and common benthic sampling devices,ARMS standardization has the advantages of low cost and coral reef friendly,which can be used as an excellent sampling method for coral reef diversity research.?3?The range of?¹³C value and?¹⁵N value of reef food web in Daya Bay was-23.22‰?-10.76‰and 4.32‰?15.82‰.The?¹³C value of potential food sources was-23.22‰?-13.27‰,and the?¹⁵N value of potential food sources ranged from 4.32‰to 11.34‰.There were significant differences between the carbon and nitrogen isotope ratios of potential food sources and consumers?P<0.05?.The composition of food sources in Daya Bay coral was complex,and the contribution of organic matter from different sources to food web was different.Phytoplankton,POM and SOM may be the main energy sources of zooplankton,and SOM had a relatively small contribution to the carbon sources of invertebrates and fish.Phytoplankton and algae were important primary producers and important carbon sources driving the food web in the coral reef ecosystem of Daya Bay.The main consumers had different nutritional positions,and the?¹⁵N values of some consumers in different groups overlap,which was related to the interspecific competition caused by their ingestion of common food organisms.The nutritional levels of consumers ranged from 1.70 to 3.64,among which the nutritional levels of gastropods,bivalves,crabs,echinoderms,fish and cephalopods were 1.84 to2.68,1.70 to 2.49,2.61 to 2.79,2.58 to 2.83,2.45 to 3.64 and 3.04 to 3.40,respectively.The difference of their nutritional levels was mainly related to their eating habits.The main consumers showed the distribution characteristics of nutrition level with less top nutrition level biological species and more middle nutrition level species.The smaller nutrition level might be related to the smaller sample length,the lower sample size and species number.There was no significant difference in carbon and nitrogen isotope ratio of benthos in different seasons?P>0.05?,which may be related to the characteristics of coral reef ecosystem habitat and the individual size of benthos collected.In spring,the food source of benthos was less,the level of nutrition in the population is different greatly,and the community competition was more intense.In general,the nutrient diversity and food web of benthos in Daya Bay were relatively stable.