On culture artefacts in coccolith morphology

Coccolith malformations occur more frequently in cultured specimens than in specimens from natural samples, a phenomenon commonly termed ‘culture artefacts’. The causes of culture artefacts are unknown. Here, we tested the effect of culture flask shape, mixing, and cell density on the morphology of Emiliania huxleyi coccoliths. While there was no effect of different culture flask types typically used in coccolithophore culturing, continuous mixing reduced the percentage of malformations by ca. 11 % in exponential-phase cells (cell density ca. 80 × 103 cells per ml) and ca. 17 % in stationary-phase cells (cell density ca. 2 × 106 cells per ml). Stationary-phase cells displayed 19 % more malformations than mid-exponential-phase cells when not mixed at all and 20 % more malformations when continuously mixed. It is concluded that the lack of mixing and unnaturally high cell densities, typical for coccolithophore stock cultures, are partly responsible for culture artefacts

Seawater carbonate chemistry, nutrients, and Calcidiscus leptoporus (strain RCC1135) growth rate and calcification rate during experiments, 2012

The coccolithophore Calcidiscus leptoporus was grown in batch culture under nitrogen (N) as well as phosphorus (P) limitation. Growth rate, particulate inorganic carbon (PIC), particulate organic carbon (POC), particulate organic nitrogen (PON), and particulate organic phosphorus (POP) production were determined and coccolith morphology was analysed. While PON production decreased by 70% under N-limitation and POP production decreased by 65% under P-limitation, growth rate decreased by 33% under N- as well as P-limitation. POC as well as PIC production (calcification rate) increased by 27% relative to the control under P-limitation, and did not change under N-limitation. Coccolith morphology did not change in response to either P or N limitation. While these findings, supported by a literature survey, suggest that coccolith morphogenesis is not hampered by either P or N limitation, calcification rate might be. The latter conclusion is in apparent contradiction to our data. We discuss the reasons for this inference

Understanding the interactive effects of ocean acidification and the availability of iron on the two Southern Ocean key phytoplankton groups – diatoms and cryptophytes

Long-term phytoplankton monitoring studies, specifically in the coastal areas of the Western Antarctic Peninsula, have shown the recurring succession of diatoms and cryptophytes wherein diatoms usually dominate during the early summer when Fe concentrations are high, which are then replaced by cryptophytes in late summer at lower Fe availability. Laboratory incubation experiments were conducted to examine how increasing pCO2 levels (400, 1000 and in the case of the diatom, 1400 µatm) and different iron availability (0.2 and 0.9 nM) will impact the two Southern Ocean phytoplankton key species Pseudo-nitzschia subcurvata and Geminigera cryophila. Results of this study exhibited a different pattern between the two species as the cryptophyte manifested generally lowered growth rates and photochemical efficiencies compared to the diatom Pseudo-nitzschia subcurvata for all pCO2-Fe treatment combinations. This suggests that G. cryophila had higher Fe requirement than the latter. The diatom was particularly sensitive to ocean acidification under Fe-deplete condition as growth strongly declined with increasing pCO2, but no OA-effect on growth was observed in the Fe-enriched treatments. In comparison, growth of the cryptophyte was stimulated by high pCO2 under high Fe availability, but remained unaffected under low Fe concentration. Hence, the two species showed varying responses wherein G. cryophila appears to be less vulnerable to ocean acidification yet greatly affected by Fe-limitation while the susceptibility of P. subcurvata to OA is enhanced under Fe-deplete condition

On culture artefacts in coccolith morphology

Coccolith malformations occur more frequently in cultured specimens than in specimens from natural samples, a phenomenon commonly termed ‘culture artefacts’. The causes of culture artefacts are unknown. Here, we tested the effect of culture flask shape, mixing, and cell density on the morphology of Emiliania huxleyi coccoliths. While there was no effect of different culture flask types typically used in coccolithophore culturing, continuous mixing reduced the percentage of malformations by ca. 11 % in exponential-phase cells (cell density ca. 80 × 103 cells per ml) and ca. 17 % in stationary-phase cells (cell density ca. 2 × 106 cells per ml). Stationary-phase cells displayed 19 % more malformations than mid-exponential-phase cells when not mixed at all and 20 % more malformations when continuously mixed. It is concluded that the lack of mixing and unnaturally high cell densities, typical for coccolithophore stock cultures, are partly responsible for culture artefacts

Seawater carbonate chemistry and growth, carbon acquisition, and species interaction of Antarctic phytoplankton species in a laboratory experiment

Despite the fact that ocean acidification is considered to be especially pronounced in the Southern Ocean, little is known about CO2-dependent physiological processes and the interactions of Antarctic phytoplankton key species. We therefore studied the effects of CO2 partial pressure (PCO2) (16.2, 39.5, and 101.3 Pa) on growth and photosynthetic carbon acquisition in the bloom-forming species Chaetoceros debilis, Pseudo-nitzschia subcurvata, Fragilariopsis kerguelensis, and Phaeocystis antarctica. Using membrane-inlet mass spectrometry, photosynthetic O2 evolution and inorganic carbon (Ci) fluxes were determined as a function of CO2 concentration. Only the growth of C. debilis was enhanced under high PCO2. Analysis of the carbon concentrating mechanism (CCM) revealed the operation of very efficient CCMs (i.e., high Ci affinities) in all species, but there were species-specific differences in CO2-dependent regulation of individual CCM components (i.e., CO2 and uptake kinetics, carbonic anhydrase activities). Gross CO2 uptake rates appear to increase with the cell surface area to volume ratios. Species competition experiments with C. debilis and P. subcurvata under different PCO2 levels confirmed the CO2-stimulated growth of C. debilis observed in monospecific incubations, also in the presence of P. subcurvata. Independent of PCO2, high initial cell abundances of P. subcurvata led to reduced growth rates of C. debilis. For a better understanding of future changes in phytoplankton communities, CO2-sensitive physiological processes need to be identified, but also species interactions must be taken into account because their interplay determines the success of a species