Abstract:

Based on the data of a Noctiluca scintillans population in northern South China Sea (107°00′- 119°00′E, 16°00′-24°00′N) obtained in project “Integrated Investigation and Assessment of China Seas” (coded as 908 project) in 2006 and 2008, we described the spatial distribution in wide geographical areas and seasonal variations of a Noctiluca scintillans population using GIS spatial analysis modeling and mapping techniques. The adaption of Noctiluca scintillans to temperature, salinity and nutrients were also discussed. The results showed that abundance of Noctiluca scintillans varied from 0.001×10 ⁴cells/m³ to 64.5×10⁴cells/m³, with an average of (0.56±3.29)×10⁴cells/m³(n = 1,424). Average abundance varied by season, spring > autumn > winter > summer, with highest and lowest abundances of (1.28±4.24)×10⁴cells/m³ (n = 356) and (0.19±0.95)×10⁴cells/m³(n = 356), respectively. The spatial distribution of Noctiluca scintillans generally decreased from alongshore to offshore areas, in a pattern of discontinuous patches. Abundance assemblage zones laid along the shores of eastern Leizhou peninsula, where it was also the peak abundance region in winter. The zones of low annunal abundance were primarily in the northern South China Sea. Dapeng Bay in eastern Guangdong Province and Pearl River Estuary were not abundance assemblage zones during summer and winter months. We found the shore of southeastern Hainan Island became high abundance zones during summer months. Compared with data of national integrated investigations completed in 1958 and 1959, Noctiluca scintillans abundance increased abruptly with an evident change of abundance assemblage zones. The seasonal variation was obvious. Average Noctiluca scintillans abundance was 27 times higher than recorded in 1959. Noctiluca scintillans populations in South China Sea required a much higher temperature than it did in East, Yellow and Bohai Seas in China. Salinity fluctuations were normally not a critical factor determining variation in Noctiluca scintillans abundance. High Noctiluca scintillans abundance was not resulted directly from high nutrient content. Water eutrophication was not the necessary condition to predict the Noctiluca scintillans bloom.

Key words: northern South China Sea, Noctiluca scintillans, spatial distribution, seasonal variation, environmental adaption