Living coccolithophore assemblages in the Yellow and East China Seas in response to physical processes during fall 2013

Abstract

Abstract Living coccolithophore assemblages collected at discrete depths (0–490 m) from eleven stations across the shelf and slope regions of the Yellow and East China Seas (YECS) during fall 2013 were analyzed using a scanning electron microscope. A total of 32 taxa were recorded, and the predominant taxa were Emiliania huxleyi, Gephyrocapsa spp., Syracosphaera spp. and Algirosphaera robusta. The body coccoliths of A. robusta exhibited an unusual morphology with incomplete hoods, which were recorded in nearly half of the samples and may represent a new variety. In addition, an agglutination relationship was observed between Gephyrocapsa coccoliths and the tintinnid Dictyocysta lepida in oligotrophic waters. Total coccolithophores reached a maximum cell abundance of 252 × 103 cells/l (on average 27.8 × 103 cells/l), with the contribution of Gephyrocapsa ericsonii, E. huxleyi and Gephyrocapsa oceanica accounting for 36.4%, 29.6% and 15.3%, respectively, of the total abundance. Coccolithophore assemblages in the YECS were a mixture of coastal, shelf and subtropical taxa, with the diversity decreasing in a radial direction from the Okinawa Trough to the inner shelves. Distinct deep-water flora existed in the Kuroshio slope waters (100–490 m), which was precisely reflected by the cluster analysis, illustrating very low percent similarity (48.1%) with the other groups. The occurrence of subtropical taxa in the coccolithophore assemblages can be used as benign warmer water signals. In the bottom turbid layers, the coccolithophore assemblages were largely composed of free coccoliths (84.3%), implying complex processes, such as cell death, resuspension and lateral advection, in the sandy and detrital waters. To clarify the relationship between the species distribution and ambient environments, a redundancy analysis (RDA) was applied to distinguish how much the variation in the taxon composition could be attributed to changes in the environmental conditions. Conclusively, salinity and temperature, which to some extent could reflect the physical properties of water stability and stratification, were key factors in driving the distribution patterns of living coccolithophores in the study areas.