Studies On The Temporal And Spatial Characteristic Of Phytoplankton Pigments Of Surface Microlayer And Subsurface Water In Dapeng Cove

To assess the effects of aquaculture on the phytoplankton, the temporal and spatial distribution of pigments and size spectrum of phytoplankton in the surface microlayer(SML)and the subsurface water(SSW) in Dapeng Cove, Guangdong, South China, from May in 2013 to June in 2014, were investigated. The dairly variations in pigments of the surface microlayer(SML) and the subsurface water(SSW) in summer and winter were also analysized.Total 21 kinds of pigments were detected from SML and SSW of Dapeng Cove.Fucoxanthin was the most abundant among pigments, indicating that the phytoplankton community was dominated by diatoms. Microphytoplankton(>20 μm) contributed most of chlorophyll a, nanophytoplankton(2.7~20 μm) came second, while the contribution of picophytoplankton(<2.7 μm) was lowest. And the seasonal variation of phytoplankton biomass was different between SSW and SML. The biomass was hightest in SSW in winter while the lowest in SML in summer. This study suggested that the SML was enriched in mciro-sized fraction of Chl a, Fuco and Peri.Our results demonstrated the significant grazing impact of oyster on phytoplankton biomass.During the culture period of oysters, average concentration of total Chl a(sum of size-fractionated Chl a) inside the farming area was around 60% lower than that at the reference site. Occurrence of phytoplankton depletion in the aquaculture zone mainly appeared in micro-sized fraction of Chl a, Fuco and Peri. In comparison, nano-sized pigments seemed to be less influenced by oyster filtration than micro-sized ones. Compared with diatoms, oysters filter feeding is more significant on dinoflagellate. Picophtoplankton abundances in aquaculture zone are significantly higher than that in non-aquaculture areas(P < 0.01). This suggests that oyster aquaculture in Dapeng Cove can stimulate the growth of picophytoplankton although, of which,the seasonal variations are mainly controlled by water temperature.The concentration of Chl a was higher in winter than that in summer. Microphytoplanton(diatom) dominated in winter. In comparison, the proportion of diatom decreased while picophytoplankton(cyanobacteria) inceased in summer. Due to high temperature and high irradiance, the concentration of Chl a had significantly decreased at mid noon. Micro-sizedfraction of other pigments also decreased at mid noon while pico-size did not. Notably, we found vertical migration of micro-sized fraction of cryptophytes cells from SSW to SML at mid noon.