Comparative Studies On Phytoplankton Community Structure Between Surface Microlayer And Subsurface Water In Daya Bay

The sea surface microlayer (SML) is an important interface between the atmosphereand the sea. This interface has unique physicochemical and biological properties. Anannual survey was conducted on the phytoplankton community and environmental factorsin Dapengao area of Daya Bay between April2013and March2014. The purpose of thisstudy is to better understand phytoplankton composition, quantitative distribution andannual variation of dominant species, and to know the characteristics of phytoplanktoncommunity structure in the SML and subsurface water (SSW). Meanwhile, phytoplanktonDNA fingerprints were analyzed by PCR-denaturing gradient gel electrophoresis(PCR-DGGE) technique. The results from this study enriched the information ofphytoplankton structure in the SML of Daya Bay, and provided a scientific basis forenvironmental protection in this sea area.A total of142taxa were identified during the survey, including132species from theSML and128from the SSW. However, the Shannon-Weaver species diversity index andevenness was low, indicating the deterioration of environments in Daya Bay in the recentyears. Diatom was the predominant group of phytoplankton, followed by dinoflagellate,and few occurrence of species in other groups such as cyanobateria, chrysophytes，cryptophytes and rhaphidophytes. The common predominant species includedChaetoceros, Skeletonema costatum, Pseudo-nitzschia and Leptocylindrus danicus, whichwere presented throughout the whole year. Meanwhile, Rhizosolenia fragilissima,Cerataulina pelagica, Guinardia striata dominated in some particular months. Thephytoplankton abundance was high as well, with the annual average cells density of2.07×106cells/L and1.48×106cells/L in the SML and SSW, respectively. The cell densitypeaked in summer, followed by winter, and was lower in spring and autumn. A high peakof S. costatum occurred in February, which resulted in winter peak of phytoplankton. Thephytoplankton structure in the SML was similar to that in the SSW, and was characterizedby the dominance of diatoms, high species richness and low species diversity. The totalphytoplankton, diatoms and dinoflagellates were enriched in the SML, particularly for the dominant diatoms.The abundances of eukaryotic phytoplankton DNA fingerprints were comparable inthe SML and the SSW, but fingerprints of cyanobacteria were significantly higher in theSML, which indicated the enrichment of cyanobacteria in the SML. The DNA fingerprintsof eukaryotic phytoplankton were most abundant in autumn, and least in winter.Furthermore, the fingerprints of cyanobacteria were higher in the warm season from latespring to early autumn. The results of cluster analysis indicated that the DNA fingerprintsof phytoplankton showed few differences between the SML and the SSW, however thesamples from the SML and the SSW still clustered together respectively. Though the DNAfingerprints can not reflect the species diversity of the whole phytoplankton community,but provide some useful information on the diversity of dominant species. Furthermore,the DNA fingerprints of cyanobacteria provide more detail information about thedistribution of cyanobacteria. The results from this study suggest that the PCR-DGGEtechnique is feasible to be used in the phytoplankton community structure analysis as aneffective supplement of the microscopic observation.