Studies on the Community Structure of Phytoplankton in the Sea near Sanmen Bay

Abstract

This paper reports the phytoplankton investigation results which were collected in 15 observation stations and a day-night continuous observation station in the sea area near Sanmen Bay (29° 00'00 "~ 29° 10'26 "N, 121° 34'43" ~ 121° 47'06 "E) in spring(April), summer (July), autumn (October) of 2007 and winter (January) of 2008. After microscopic observation and identification, a total of 6 phyla, 56 genera, 146 species were identified in the sea near Sanmen Bay. The seasonal species change was spring (101)> autumn (96)> summer (96)> winter (85). The cell abundance of phytoplankton in the sea near Sanmen Bay was 0.72103～1.3106 cells /dm3, and the average cell abundance was 5.13104 cells /dm3. The mean cell abundance in winter was 1.27105cells/dm3 >4.72104cells/dm3 in autumn > 1.63104 cells/dm3 in spring > 2.51103cells/dm3 in summer. During the 24-hour continuous observation, in the day time, particularly in the afternoon, the photosynthesis was strong, and the cell abundance of phytoplankton was high; at night, especially in the latter half of the night or wee hours, the photosynthesis was weak, and the cell abundance of phytoplankton was low. The dominant species of phytoplankton in the Sanmen Bay was Skeletonema costatum. Ecological types of phytoplankton can be divided into three groups: (1) inner bay and coastal temperate group; (2) eurythermal and euryhaline group; (3) warm water off-shore group. Inner bay and coastal eurythermal and euryhaline group was the dominant group. The amounts of other groups were less. Totally 64 red-tide species were observed in the sea area near Sanmen Bay, of which, diatoms was predominant, 40 species; dinoflagellates was 19 species; Cyanophyta was 2 species; Euglena、Chrysophyceae and Protozoa was 1 specie respectively. The average cell abundance of the main red-tide organisms in the sea area near Sanmen Bay was 5.6102 cells/dm3～1.2105 cells/dm3. The dominant species composition and community structure of phytoplankton were mainly composed of diatoms, such as Skeletonema costatum, Ditylum brightwelli, Coscinodiscus jonesianus, Thalassiosira eccentrica, Leptocylindrus danicus, Chaetoceros lorenzianus; pyrrophyta, such as Ceratium fusus, Ceratium tripos, Ceratium furca etc.