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Morphology and bloom dynamics of Cochlodinium geminatum (Schütt) Schütt in the Pearl River Estuary, South China Sea

Shen, Ping-Ping, Li, Ya-Nan, Qi, Yu-Zao, Zhang, Lv-Ping, Tan, Ye-Hui, Huang, Liang-Min
Harmful algae 2012 v.13 pp. 10-19
Dinophyceae, biomass, chlorophyll, chloroplasts, dry season, estuaries, multivariate analysis, nutrient content, phytoplankton, rivers, salinity, scanning electron microscopy, surface water, temperature, turbidity, South China Sea
An unarmored dinoflagellate bloom of Cochlodinium geminatum (Schütt) Schütt has been identified in the Pearl River Estuary, South China Sea during the severe dry season, from late October to early November, 2009, when temperature and salinity ranged between 20.0–27.2°C and 10.6–33.4, respectively. Light and scanning electron microscopy were used to identify the characteristics of C. geminatum and provided the clear morphological structure for this species. The organism was primarily found in chains of two cells or single cell, and no longer chains were observed. Cells were irregularly spherical or slightly dorso-ventrally, with size ranged between 28 and 36μm and longer than wide. A large nucleus in the center with numerous golden chloroplasts was present, and the cingulum made 1.5 turns around the cell. The concentration of C. geminatum ranged from 10² to greater than 10⁷cellsl⁻¹ during the bloom period. Nutrient concentration ranges during the bloom were 1.29–81.00μM NO₃, 0.14–12.14μM NO₂, 0.21–6.29μM NH₄, 0.23–6.26μM PO₄ and 3.29–171.43μM SiO₃, respectively. Total biomass expressed in terms of chlorophyll a ranged from 2.44 to 135.45μgl⁻¹, with an average 19.9μgl⁻¹ in surface water throughout the PRE. Two main clusters corresponding to the water sectors were defined with multivariate analysis (cluster and nMDS). Based on the composition and abundance of phytoplankton, spatial variations were observed at a significant level (ANOSIM, R=0.44, P<0.01). Although the pairwise correlation analysis detected no significant effect of any single environmental variable on the abundance of C. geminatum, the multivariate analysis (BIO-ENV) between biotic and abiotic variables resulted in the best variables combination with all measured factors involved (temperature, salinity, turbidity, NO₃, NO₂, NH₄, PO₄ and SiO₃) which showed a combined effect during the bloom of C. geminatum in the Pearl River Estuary (ρw=0.477).