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

Abstract

An unarmored dinoflagellate bloom of Cochlodinium g eminatum (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. g eminatum 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 36 μm 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. g eminatum ranged from 10 2 to greater than 10 7 cells l −1 during the bloom period. Nutrient concentration ranges during the bloom were 1.29–81.00 μM NO 3, 0.14–12.14 μM NO 2, 0.21–6.29 μM NH 4, 0.23–6.26 μM PO 4 and 3.29–171.43 μM SiO 3, respectively. Total biomass expressed in terms of chlorophyll a ranged from 2.44 to 135.45 μg l −1, with an average 19.9 μg l −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. g eminatum, the multivariate analysis (BIO-ENV) between biotic and abiotic variables resulted in the best variables combination with all measured factors involved (temperature, salinity, turbidity, NO 3, NO 2, NH 4, PO 4 and SiO 3) which showed a combined effect during the bloom of C. g eminatum in the Pearl River Estuary ( ρ w = 0.477).