Ecological characteristics and influencing factors of phytoplankton 

community in spring and summer in the East China Sea

Abstract: In order to understand the ecological characteristics of phytoplankton community in the East China Sea in recent years, the structural characteristics of phytoplankton community in the East China Sea and its relationship with typical environmental factors (water temperature, nutrient content and structure, CODMn and suspended solids concentration) were analyzed by investigating the basic elements of phytoplankton and environment in the East China Sea in May and August from 2015 to 2017. Results showed that the nitrogen phosphorus ratio in the study area of the East China Sea in spring was 2035. The dominant species of phytoplankton in spring were mainly composed of Coccinodiscus oculusiridis, Coccinodiscus jonesianus and Skeletonema costatum. The ratio of nitrogen to phosphorus in summer was higher than that in spring and was much higher than 16∶1. The dominant species in summer was Skeletonema costatum. According to the investigation, the number of phytoplankton in the coastal waters was significantly higher than that in the continental shelf of the East China Sea. The redundancy analysis results showed that from spring of 2015 to 2017, the environmental factor that had a great impact on phytoplankton in the investigated sea area was active phosphate. From summer of 2015 to 2017, the environmental factors that had a great impact on phytoplankton in the investigated sea area were inorganic nitrogen, active phosphate and chemical oxygen demand.

In S3 and S5 of the fishing ground in the Yangtze River Estuary, the transparency of the water body was high, and the content of inorganic nitrogen and active phosphate in the water body was relatively high, which provided a good nutritional condition for the largescale propagation of phytoplankton. This phenomenon may be related to the thin layer distribution of phytoplankton in the Yangtze Estuary. According to the data from 2015 to 2017, the average abundance of phytoplankton in spring and summer was 3.0 × 104 cell · L-1 and 2.7× 104 cell · L-1. Based on the data collected from the continental shelf survey network of the East China Sea from 1997 to 2000, the phytoplankton abundance in autumn was the highest (211.9 × 104 cell · m-3）, followed by summer (50.4 × 104 cell · m-3） and winter (11.4 × 104 cell · m-3）and the lowest was in spring (2.0 × 104 cell · m-3）. From 1997 to 2000, the average phytoplankton abundance of four seasons was 68.9 × 104 cell · m-3. The coastal area of the East China Sea had a high abundance of phytoplankton due to the impact of the fresh water of the Yangtze Estuary, the Qiantang River and the coastal current of the East China Sea. 

The results of redundancy analysis (RDA) using Canoco software showed that in spring of 2015, the environmental factors that had a great impact on the distribution of phytoplankton in the study area were pH, DO and active phosphate. DO, pH and active phosphate environmental variables were positively correlated with RDA1. In summer, the environmental factors that had great influences on the distribution of phytoplankton in the study area were COD and active phosphate. Environmental variables such as COD, active phosphate, DO, inorganic nitrogen and pH were positively correlated with RDA1. In spring of 2016, the environmental factors that had great impacts on phytoplankton were water temperature, DO, inorganic nitrogen and COD. Environmental variables such as water temperature, DO, inorganic nitrogen and COD were positively correlated with RDA1. In summer, water temperature and inorganic nitrogen were the environmental factors that had great negative impacts on Skeletonema costatum. Environmental variables such as water temperature and inorganic nitrogen were negatively correlated with RDA1. In spring of 2017, the environmental factor that had a great negative impact on the dominant species of phytoplankton was active phosphate. The active phosphate environment variable was negatively correlated with RDA1. In summer, inorganic nitrogen was the most important environmental factor affecting Skeletonema costatum. Inorganic nitrogen environmental variables were positively correlated with RDA1.

Keywords: East China Sea; phytoplankton community; ecological characteristics; environmental factors; spring and summer