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Abstract

Variations in phytoplankton community structure in different salt marshes in the Dongtan wetland of the Yangtze River Estuary.

Abstract

Based on data of phytoplankton in the salt mashes waters from May to December in 2015, the study analyzed the monthly variations in phytoplankton community structure in 4 types of salt marshes (HS, Scirpus mariqueter; HZ, early stage of Spartina alterniflora invasion; HH, later stage of Spartina alterniflora invasion; LW, Phragmites australis). The results showed that 64 species (including unidentified genus) belonging to 4 phylum were collected. The number of diatom species was the largest (48 species, including the unidentified genus), accounting for 73.8% of the total number of species. The 10 species of Cyanophyta followed by and Chlorophyta (6 species) was the third. But only 1 species of Pyrrhophyta was collected. The 14 species dominated in the phytoplankton community, which were Skeletonema costatum (Y=0.76), Nitzschia lorenziana, Pleurosigma affine, et al. From May to August, the number of species of phytoplankton in the salt marshes was higher than that in the periods of September-December. The peak density of phytoplankton was 8.96×104 cell.L-1 in July. In all types of salt marshes, the mean monthly density of diatom species was obviously higher than other species, but the density of Pyrrhophyta-species was the lowest. The number of species and density of phytoplankton had no obvious differences between HS and HZ habitats (P>0.05), while no significant difference was found between HH and LW habitats (P>0.05). The mean monthly density of phytoplankton in the former two habitats was 3.8 times more than that in the later habitats, because there was very high density of diatoms in the former two habitats (HS and HZ). The Margalef's species richness indexes (D) of four habitats in May-August was obviously higher than that in September-December, although there was no significant difference between any two habitats. The mean Pielou's indexes (J) in October and November were obviously lower than that in other months, while J′ values in July (in HS and HZ habitats) and September (in HZ and HH) were both lower than 0.1. The Shannon-Weaver index (H′) values showed similar changes with the J index, but the H′ values in July for HS and HZ habitats were both lower than 0.2, because the highest density of Skeletonema costatum was collected in this month. From the results of community clustering and non-Metric Multidimensional scaling plot, it is indicated that it is difficult to distinguish the differences in the phytoplankton community for 4 types of salt marshes and they can almost be divided into two groups in terms of timing (May-August and September-December). As in whole, there were obvious monthly changes in phytoplankton community in structure of salt marshes, but it is found that there is no significant variation in the same elevation.