TESTING THE EFFECTS OF ELEVATED PCO₂ ON COCCOLITHOPHORES (PRYMNESIOPHYCEAE): COMPARISON BETWEEN HAPLOID AND DIPLOID LIFE STAGES¹

Abstract

The response of Emiliania huxleyi (Lohmann) W. W. Hay et H. Mohler, Calcidiscus leptoporus (G. Murray et V. H. Blackman) J. Schiller, and Syracosphaera pulchra Lohmann to elevated partial pressure of carbon dioxide (pCO2 ) was investigated in batch cultures. We reported on the response of both haploid and diploid life stages of these three species. Growth rate, cell size, particulate inorganic carbon (PIC), and particulate organic carbon (POC) of both life stages were measured at two different pCO2 (400 and 760 parts per million [ppm]), and their organic and inorganic carbon production were calculated. The two life stages within the same species generally exhibited a similar response to elevated pCO2 , the response of the haploid stage being often more pronounced than that of the diploid stage. The growth rate was consistently higher at elevated pCO2 , but the response of other processes varied among species. Calcification rate of C. leptoporus and of S. pulchra did not change at elevated pCO2 , whereas it increased in E. huxleyi. POC production and cell size of both life stages of S. pulchra and of the haploid stage of E. huxleyi markedly decreased at elevated pCO2 . It remained unaltered in the diploid stage of E. huxleyi and C. leptoporus and increased in the haploid stage of the latter. The PIC:POC ratio increased in E. huxleyi and was constant in C. leptoporus and S. pulchra. Elevated pCO2 has a significant effect on these three coccolithophore species, the haploid stage being more sensitive. This effect must be taken into account when predicting the fate of coccolithophores in the future ocean.

Physiology regulates the relationship between coccosphere geometry and growth phase in coccolithophores

“…Mean exponential growth rates for C. braarudii at 15 • C were 0.68 d −1 . These values are well within the ranges reported in other studies carried out at similar temperatures for Calcidiscus (Langer et al, 2006;Buitenhuis et al, 2008;Fiorini et al, 2010Fiorini et al, , 2011Langer et al, 2012;Candelier et al, 2013;Müller et al, 2014) and H. carteri (Stoll et al, 2002;. Exponential growth rates of 0.4-0.5 d −1 signify that roughly half of the culture population undergoes cell division each day.…”

Environmental controls on coccolithophore calcification

“…Von Dassow et al (2009) showed for Emiliania huxleyi that transcript levels of genes whose products are involved in coccolithogenesis (Ca 2+ , H + and HCO 3 − transporters) are expressed much more in the diploid (heterococcolith) than in the haploid (holococcolith) phase which has non-calcified coccoliths. The few studies concerning environmental effects on holococcoliths (Quintero-Torres et al 2007, Fiorini et al 2011a, Pedrotti et al 2012 will be discussed in the relevant sections.…”

“…There is no evidence of the effects of carbonate system chemistry on holococcolith-bearing haploid cells. This was examined by Fiorini et al (2011a) for Calcidiscus leptoporus and Syracosphera pulchra; however, the PIC of the haploid cells was below the detection limits. This may be of interest to pursue because holococcoliths persisted in the fossil record through variations in atmospheric and ocean chemistry (Medlin et al 2008).…”

Morphology of <i>Emiliania huxleyi</i> coccoliths on the northwestern European shelf – is there an influence of carbonate chemistry?

“…Early experimental work with laboratory cultures and large-scale semi-enclosed field cultures, mesocosms, suggested that there was a clear reduction in calcification rates with increasing pCO 2 (Riebesell et al, 2000;Riebesell, 2004;Zondervan et al, 2002;Engel et al, 2005). They did, however, note that other effects such as growth rate and cell size changes could confuse this response, that the response was often muted (also shown by Fiorini et al, 2011) and that it was important to look at changes in the ratio of calcification to photosynthetic carbon fixation and at calcification rates per cell.…”