Insight into <i>Emiliania huxleyi</i> coccospheres by focused ion beam sectioning

Abstract

Abstract. Coccospheres of a cultured Emiliania huxleyi clone were sampled in the exponential growth phase and sectioned using a focused ion beam microscope. An average of 69 sections and the corresponding secondary electron micrographs per coccosphere provided detailed information on coccosphere architecture. The coccospheres feature 2-3 layers on average and 20 coccoliths per cell, of which only 15 can be seen in conventional scanning electron micrographs. The outer coccosphere diameter was positively correlated with the number of coccolith layers. By contrast, the inner coccosphere diameter (around 4.36 µm), and hence the cell diameter, was quasi-constant. Coccoliths were not evenly distributed across the coccosphere, resulting more often than not in one part of the coccosphere displaying more coccolith layers than the other. The architectural data allowed for the calculation of the PIC / POC ratio, the density and the sinking velocity of individual cells. The correlation of these parameters has implications for the ongoing debate on the function of coccoliths.

Ocean warming modulates the effects of acidification on Emiliania huxleyi calcification and sinking

“…From now on, we will use the subscript PIC C/N , POC C/N , and PIC/POC C/N to differentiate carbon quotas of filtered samples, from carbon quotas of attached coccoliths and sinking rates estimates, PIC SEM POC SEM and PIC/POC SEM . PIC C/N and POC production (P PIC and P POC ) were estimated from cellular inorganic and organic carbon content and growth rates (l) according to P 5 l * cellular carbon content PIC, POC, density, and sinking rates estimates Cellular PIC SEM content of attached coccoliths was calculated according to Hoffmann et al (2015), using the number of coccoliths per cell (coccosphere) and the mass of a single coccolith. The number of coccoliths per cell was analyzed using SEM images, counting the visible coccoliths per sphere and assuming that they constitute 75% of the total coccosphere (Hoffmann et al 2015).…”

“…The overall cell density was estimated according to the method of Hoffmann et al (2015). For this, we used cellular PIC SEM content of attached coccoliths, POC C/N quota measured with a C/N Euro analyzer, cell diameter measured using a Multisizer III Coulter counter and coccosphere diameter measured from SEM images using the software GIMP v2.6.…”

“…In this study we estimated the overall cell density and sinking rates of E. huxleyi RCC1827 using a recently proposed method (Hoffmann et al 2015). Sinking rate calculations were based on cellular density estimates and Stokes law.…”

“…Conversely, the sinking of living individual cells out of the photic zone might diminish the standing stock and therefore be disadvantageous. Coccolithophore sinking rate is positively correlated to PIC/POC (Hoffmann et al 2015). So a future decrease in the PIC/POC due to increased CO 2 could lead to reduced sinking rate.…”

“…Here, we therefore analyze the response of E. huxleyi to an increase in CO 2 and temperature in terms of POC as well as PIC production, the PIC/POC and the sinking rate of individual cells. We use a novel approach to calculate sinking rate from cell-architecture (Hoffmann et al 2015).…”