Zooplankton community structure and seasonal patterns in the Zhanjiang Harbor waters, China

To improve our knowledge regarding the physical and biological processes relating the plankton ecology in typical subtropical estuaries, species composition, abundance and diversity of zooplankton were investigated during four cruises conducted in Zhanjiang Harbor waters, China, between Nov, 2008 and Feb, 2009. A total of 128 species of zooplankton and 9 species/assemblages of planktonic larvae were identified, including 49 species of Copepods, followed by Medusas (16 species), Protozoa (12 species), Decapods(10 species) and Chaetognatha(10 species), etc. The species/ assemblages that occurred in spring, summer, autumn and winter were 51, 45, 27, 59 species, respectively. In all, the abundance of zooplankton in the harbor inner waters was higher than that off the mouth of the Harbor waters, and the abundance was 1.1×10²±1.5×10² individuals·m^-3(ind. ·m^-3), 1.5×10²±2.3×10² ind·m^-3, 4.1×10±3.4×10 ind·m^-3, 5.6×10±5.0×10 ind·m^-3 in spring, summer, autumn and winter, respectively. The seasonal turnover rate of dominant zooplankton species was higher than 63%, indicating relative large seasonal variation of the community structure. The Shannon-Winner diversity index averaged 3.08 annually, which increased from spring to summer, and decreased form autumn and winter to some extent. And the values of Evenness index and richness index showed similar trends as the diversity index seasonal variation. The value of community diversity was the highest in the middle waters (3.14), the second was in the mouth of the Harbor waters (3.10), and the last was in the coastal waters (2.99). Using step-wise regression method, the environmental adaption of zooplankton dominant species abundance analysis showed that the chlorophyll a, phytoplankton abundance, an- sea water temperature had great effects on the dominant zooplankton species abundance, and the effects varied as the different species abundance, also indicating the differences in ecological niches among dominant zooplankton species.