The Investigation Of Community Structure Of Plankton And Density Of Coral Recruitment In Dazhou Island

This study was conducted in the last three seasons of 2014 and in the spring of 2015,which respectively investigated the characteristic of community structure and the time-space distribution of the plankton community in six sites of the front and back harbour in DaZhou island waters. This study also investigated the density of coral recruitment in the back port in May 2015 and May 2016.According to the investigation, there were 5 kinds and 83 species of phytoplankton in total, including 46 species of bacillariophyta which accounted for 55 percent of algae species, 25 species of dinoflagellate accounted for 30 percent, 4 species of cyanophyta,5 species of chlorophyta , 3 species of cryptophyta, which accounted for 5 percent, 6 percent and 4 percent of the algae species respectively. Prorocentrum lima, a poisonous algae of dinoflagellate, appeared all the year round and belonged to the community of dominant species in summer and autumn. Compared to the first three seasons, the cell density of algae had a increase of 70 times or so and red tides occurred in the sea area already in the spring of 2015.There were 5 kinds and 46 species of zooplankton in total, the main groups were copepods and protozoa, accounting for 34.78 percent and 21.74 percent of species respectively. The zooplankton changed obviously from the summer of 2014 to the spring of 2015, the Planktonic larvae gradually reduced, however the protozoa on the contrary.Ciliophora, the first dominant species in the spring of 2015, was not the dominance in the last three seasons, the advantage and cell density of Ciliophora were very high in spring which became one of the red tide organisms of the spring red tides.The Plankton in the front and back habour showed a regular change with the seasons, there were a largest number of phytoplankton species in winter and the least in summer. The cell density in the front harbour living areas was obviously higher than that of other sites, there were few species of plankton, bigger cell density, higher pollution in back harbour living areas and front harbour experimental area; There were less plankton species and unstable community structure in the back habour experimental area and conservation area, which were easily affected by environment. The Shannon-Wiener was increased first and then decreased from the summer of 2014 to the spring of 2015, The Shannon-Wiener was decreased in summer and autumn and its community structure was unstable; the Shannon-Wiener reached the highest in winter, under the condition of rich nutrient,temperature became the limited factor for algae growth, Low temperature made it hard for the algae to grow, so that the plankton communities tend to be stable.The coverage of coral reefs in the back harbour was about 38.96 percent in DaZhou island. the Montipora digitata accounted for 21.5 percent of all the coral, which was the dominant community type. The density of coral recruitment was 0.0844 (ind./m2) in 2015 and 0.1592 (ind./m2) in 2016. The Pocillopora sp. was the main type. The density of coral recruitment was increasing obviously and the coral reef ecosystem recovering slowly.