Phytoplankton pigments and functional community structure in relation to environmental factors in the Pearl River Estuary

Abstract

Summary Two cruises were undertaken in the Pearl River Estuary in November 2011 and March 2012 to analyze the distribution of phytoplankton pigments and to define the relationships of pigment indices and functional community structure with environmental factors. Among 22 pigments, 17 were detected by high-performance liquid chromatography. Chlorophyll a was found in all samples, with a maximum of 7.712 μg L −1 in spring. Fucoxanthin was the most abundant accessory pigment, with mean concentrations of 2.914 μg L −1 and 0.207 μg L −1 in spring and autumn, respectively. Chlorophyll a , chlorophyll c 2 , fucoxanthin, diadinoxanthin, and diatoxanthin were high in the northern or northwest estuary in spring and in the middle-eastern and northeast estuary in autumn. Chlorophyll b , chlorophyll c 3 , prasinoxanthin, and peridinin were similarly distributed during the two cruises. Chlorophyll a and fucoxanthin positively correlated with nutrients in spring, whereas 19′-hex-fucoxanthin and 19′-but-fucoxanthin negatively correlated. The biomass proportion of microphytoplankton (BP m ) was higher in spring, whereas that of picophytoplankton (BP p ) was higher in autumn. BP m in spring was high in areas with salinity p and the biomass proportion of nanophytoplankton (BP n ) were high in areas with salinity >30. BP m increased but BP n reduced with the increase in nutrient contents. By comparison, BP p reduced with the increase in nutrient contents in spring, but no relationship was found between BP p and nutrient contents in autumn. The ratios of photosynthetic carotenoids to photoprotective carotenoids in the southern estuary approached unity linear relationship in spring and were under the unity line in autumn.