Study on the ecological characteristics of phytoplankton community in Zhanjiang Bay

Seasonal investigations on phytoplankton community and environmental factors were carried out in Zhanjiang Bay of Guangdong,China,in February(winter),May(spring),August(summer) and November(autumn) of 2009.The total 311 species in 97 genera(including varieties and forms) were found out in this sea area: 178 species occurred in spring,142 in summer,117 in autumn,and 92 in winter.Taxonomically,209 species in 54 genera were Bacillariophyta,accounting for 67.2 % of all species;71 species in 20 genera were Pyrrophyta,accounting for 22.8 %;14 species in 9 genera were Cyanophyta,accounting for 4.5 %;11 species in 9 genera were Chlorophyta,accounting for 3.5 %;2 species in 2 genera were Chrysophyta,accounting for 0.6 %;2 species in 1 genus were Euglenophyta,accounting for 0.6 %;1 species in 1 genus was Cryptophyta,accounting for 0.3 % and 1 species in 1 genus was Raphidophyceae,accounting for 0.3 %.19 dominant species were scrutinized,of which 7 were in winter,4 in spring,7 in summer and 7 in autumn.All the dominant species belong to Bacillariophyta.The majority of dominant species were Skeletonema costatum,Chaetoceros curvisetu,Asterionellopsis glacialis,Eucampia zoodiacus,Leptocylingdrus danicus and Nitzschia paradoxa.No dominant species was widespread in all seasons.All the dominant species had eurythermic and euryhaline characteristics of subtropical community structure along the seashore.33 species occurred in all seasons,and 34~69 species in two seasons.The Jaccard similarity coefficient ranged 0.17~0.31,implying obvious seasonal succession.The average diversity index and evenness were 3.02 and 0.43,respectively,indicating the lasting community composition in this sea area.The average cell abundance of phytoplankton ranged from 13.60×104 to 67.33 ×104 cells/L,with the maximum in summer,the second abundance in spring and the minimum in winter.The scenario was particular since phytoplankton in other sub-tropical areas often bloomed in spring or autumn.The abundance of phytoplankton was significantly correlative to the chlorophyll a and the water temperature,and coefficient correlation was 0.633 and 0.418(p0.01,n=112,2-tailed),respectively.It was negatively related to the DIN and silicate,and coefficient correlations were-0.493 and 0.378(p0.01,n=112,2-tailed),respectively.No correlation to the other factors was found.