Studies On Phytoplankton Community Structure And DNA Fingerprints Of Surface Microlayer And Subsurface Water From Typical Sea Areas Of Guangdong Province

Water samples from the surface microlayer(SML) and the subsurface water(SSW) were collected from four typical sea areas of Guangdong Province, Daya Bay, Baisha Bay, Guishan Island sea area and Guanghai Bay between Apirl and December 2014. DNA fingerprints of phytoplankton were analyzed using PCR-denaturing gradient gel electrophoresis(PCR-DGGE) technique, and phytoplankton was observed under the light microscope as well. Nutrients and other environmental factors were measured. Daily changes of phytoplankton community in the SML and SSW from Daya Bay were studied in winter and summer. The purpose of this study is to understand characteristics of phytoplankton community and genetic diversity in the SML in subtropical sea areas, and to know daily changes of phytoplankton community structure in the SML. The results of this study would provide some scientific basis for the protection of the SML environments. The results are concluded as following:1. Phytoplankton community structure was dominated by diatoms in all these four sea areas. Percentage compositions of diatoms were from 21.3% to 99.9% in each sample, and the avergae percentages ranged from 48.5% to 99.1% in each sea area. However, there were some differences between phytoplankton community structure in the SML and SSW. Cell densities and percentage compositions of cyanobacteria were significantly higher in the SML of Daya Bay in summer and in Baisha Bay.2. The species richness and cell densities decreased when water temperature was over 30℃ in summer. For example, cell densities were ca. 104 cells/L in two surveys conducted in summer, and the species numbers were 21 species and 32 species, respectively. However, cell densities and species numbers were much higher in samples collected from spring, autumn, and winter, when water temperatures were suitable for the growth of phytoplankton. Species numbers were as high as 47~79 species, and cell densities were over 106 cells/L in surveys conducted in Baisha Bay, Guishan Island sea area and daily changes survey in winter.3. Overall phytoplankton and diatoms were significantly enriched in the SML with the maximum enrichment factors(EF) of 17.11 and 17.64, respectively. Futher, the dominant diatom species, such as Skeletonema costatum, were much more enriched, with the highest EF of 58.32. Generally, dinoflagellates did not enriched in the SML, and the highest EF was 3.56. Furthermore, the enrichments in the SML were higher at the higher densities of phytoplankton.4. Phytoplankton community structures were similar in early morning, mid noon and late afternoon in winter, and diatoms were the preponderant group. The species richness and abundance were higher in noon and late afternoon. However, daily changes in phytoplankton community were obvious in summer. The species richness and abundance were higher in early morning and late afternoon than those in mid noon due to the cooperation of high temperature and high irradiance in mid noon. The overall phytoplankton and diatoms were enriched in the SML As well.5. Nitrogen(N) was sufficient in these four sea area in this study. The growth of phytoplankton was mostly limited by phosphorus(P), next by silica(Si). NO3-N and NH4-N were the two major contributions to dissolved inorganic nitrogen(DIN), and their average percentage compositions between 26.4%~71.8% and 21.6%~60.1%, respectively. Dossolved organic nitrogen(DON) was the dominant composition in total nitrogen(TN), with the maximum average percentages of 82.9%. Dossolved organic phosphorus(DOP) and partical organic phosphorus(POP) were the main compositions in total phosphours(TP). There were no significant enrichments in the SML for all nutrients.6. The DNA fingerprints by PCR-DGGE technique reflected diversity of species with dominance over 0.1%~0.5% in phytoplankton communities with one or two pre·ponderant species. However, in phytoplankton communities without obviously preponderant species, the DNA fingerprints were comparable with sepcies richness from microscopical observations, and thus more accurately reflected the genetic diversity of phytoplankton.