Size structure of biomass and primary production of phytoplank-ton:environmental impact analysis in the Dongsha natural gas hydrate zone,northern South China Sea

• Published in: 海洋学报（英文版） Vol. 37; no. 1; pp. 97 - 107
• Main Authors: KANG Jianhua, LIANG Qianyong, WANG Jianjun, LIN Yili, HE Xuebao, XIA Zhen, ZHENG Xinqing, WANG Yu
• Format: Journal Article
• Language: English
• Published: Third Institute of Oceanography, State Oceanic Administration, Xiamen 361005, China%Guangzhou Marine Geological Survey, China Geological Survey, Guangzhou 510760, China 2018
• Subjects: size fractionation; biomass; primary production; phytoplankton; gas hydrate; northern South China Sea
• ISSN: 0253-505X; 1869-1099
• DOI: 10.1007/s13131-017-1123-y

The size-fractionated biomass and primary production of phytoplankton, and the influence of environmental factors on it were studied in the Dongsha natural gas hydrate zone of the northern South China Sea in May 2013. Low nutrient, low chlorophyll a (Chl a) and primary productivity characteristics were found in these waters. The phenomena of subsurface Chl a maximum layers (SCMLs) and primary production maximum layers (SPMLs) were observed in the Dongsha waters. There were significant differences in the size-fractionated biomass and primary production that showed picophytoplankton>nanophytoplankton>microphytoplankton in terms of biomass and degree of contribution to production. Vertical biomass distribution indicated there were considerable differences among different phytoplankton within the euphotic zone (Zeu) in spring. For example, microphytoplankton was distributed evenly in the euphotic layer and nanophytoplankton was mainly distributed in the subsurface or in the middle of the euphotic layer, while picophytoplankton was mainly distributed in the middle or bottom of the euphotic layer. Smaller cell size and larger relative surface area allow picophytoplankton to benefit from nutrient competition and to hold a dominant position in the tropical oligotrophic waters of low latitudes. There was a positive correlation between size-fractionated biomass and temperature with pH and a negative correlation between size-fractionated biomass and silicate with phosphate. There was a positive correlation between size-fractionated primary production and temperature and a negative correlation between size-fractionated biomass and salinity with phosphate. Phosphate was an important factor influencing the size structure of phytoplankton. Meanwhile, irradiation and the euphotic layer were more important in regulating the vertical distribution of size-fractionated phytoplankton in the Dongsha natural gas hydrate zone.