Coccolithophore responses to environmental variability in the South China Sea: species composition and calcite content

Abstract

Abstract. Coccolithophore contributions to the global marine carbon cycle are regulated by the calcite content of their scales (coccoliths) and the relative cellular levels of photosynthesis and calcification rates. All three of these factors vary between coccolithophore species and with response to the growth environment. Here, water samples were collected in the northern basin of the South China Sea (SCS) during summer 2014 in order to examine how environmental variability influenced species composition and cellular levels of calcite content. Average coccolithophore abundance and their calcite concentration in the water column were 11.82 cells mL−1 and 1508.3 pg C mL−1, respectively, during the cruise. Water samples can be divided into three floral groups according to their distinct coccolithophore communities. The vertical structure of the coccolithophore community in the water column was controlled by the trophic conditions, which were regulated by mesoscale eddies across the SCS basin. The evaluation of coccolithophore-based calcite in the surface ocean also showed that three key species in the SCS (Emiliania huxleyi, Gephyrocapsa oceanica, Florisphaera profunda) and other larger, numerically rare species made almost equal contributions to total coccolith-based calcite in the water column. For Emiliania huxleyi biometry measurements, coccolith size positively correlated with nutrients (nitrate, phosphate), and it is suggested that coccolith length is influenced by light and nutrients through the regulation of growth rates. Larger-sized coccoliths were also linked statistically to low pH and calcite saturation states; however, it is not a simple cause and effect relationship, as carbonate chemistry was strongly co-correlated with the other key environmental factors (nutrients, light).

Environmental drivers of coccolithophore abundance and calcification across Drake Passage (Southern Ocean)

“…Hence, with information on the species (or morphotype) present and measurements of coccolith size it is possible to estimate coccolith calcite content (e.g. Poulton et al, 2011;Young et al, 2014;Jin et al, 2016). Together, these three metrics (cell-CF, coccolith calcite, coccolith production rates) allow for greater insight into the calcification of natural communities than can be obtained from bulk CP measurements alone.…”

“…In order to examine changes in calcification, we made estimates of cellular coccolith production rates (Poulton et al, 2010(Poulton et al, , 2013Charalampopoulou et al, 2011) from cell-CF and estimates of coccolith calcite content using biometric A. Charalampopoulou et al: Coccolithophores across Drake Passage 5919 measurements Young et al, 2014;Jin et al, 2016). Examination of such trends in cellular calcification across environmental gradients allows for changes due to variability in both cell numbers and cellular calcification to be taken into account: bulk measurements of (community) CP may be driven by variability in both (Poulton et al, 2010.…”

Two Production Stages of Coccolithophores in Winter as Revealed by Sediment Traps in the Northern South China Sea

“…Coccolith assemblages were dominated by three species, Gephyrocapsa oceanica , Emiliania huxleyi , and Florisphaera profunda , comprising more than 98% of the total coccolith count (Figure S3 in the supporting information). F. profunda lives at a water depth interval of ~75–100 m, well below the deep chlorophyll maximum (DCM, ~60 m) in summer, thus indicating their deep water (lower photic) ecology in the SCS (Jin et al, ). Most of the Noëlaerhabdaceae coccolithophores' ( E. huxleyi and G. oceanica ) cells are found at the DCM depth, which also indicates that they are productivity representatives (Jin et al, ).…”

“…Our previous living coccolithophore investigation indicated that both G. oceanica and E. huxleyi were the main contributors for the coccolithophore abundance that corresponded to the DCM in the water column (Jin et al, ). These two species were also found to be the predominant species in the upper photic assemblages in surface sediments of the SCS (Cheng & Wang, ; Fernando et al, ), indicating a high coccolithophore productivity and water fertility in the SCS basin (Jin et al, ). However, no subtle differences in the ecology of living G. oceanica and E. huxleyi populations were well documented in the study area.…”

“…Model results have shown that new production is ~32% lower in anticyclonic eddies than the basinal mean in the SCS (Xiu & Chai, ). Coccolithophore assemblages are also changed with the eddy settings across the SCS basin, with low populations of E. huxleyi and G. oceanica cells in an anticyclonic eddy (Jin et al, ).…”