Phosphorus limitation and heat stress decrease calcification in <i>Emiliania huxleyi</i>

Abstract

Abstract. Calcifying haptophytes (coccolithophores) sequester carbon in the form of organic and inorganic cellular components (coccoliths). We examined the effect of phosphorus (P) limitation and heat stress on particulate organic and inorganic carbon (calcite) production in the coccolithophore Emiliania huxleyi. Both environmental stressors are related to rising CO 2 levels and affect carbon production in marine microalgae, which in turn impacts biogeochemical cycling. Using semi-continuous cultures, we show that P limitation and heat stress decrease the calcification rate in E. huxleyi. However, using batch cultures, we show that different culturing approaches (batch versus semi-continuous) induce different physiologies. This affects the ratio of particulate inorganic (PIC) to organic carbon (POC) and complicates general predictions on the effect of P limitation on the PIC / POC ratio. We found heat stress to increase P requirements in E. huxleyi, possibly leading to lower standing stocks in a warmer ocean, especially if this is linked to lower nutrient input. In summary, the predicted rise in global temperature and resulting decrease in nutrient availability may decrease CO 2 sequestration by E. huxleyi through lower overall carbon production. Additionally, the export of carbon may be diminished by a decrease in calcification and a weaker coccolith ballasting effect.

Coccolithophore community response to ocean acidification and warming in the Eastern Mediterranean Sea: results from a mesocosm experiment

“…In addition, laboratory experiments exposing coccolithophores to various types of physiological stresses (i.e. OA 112 , 113 , OW 38 , 104 , 113 – 115 and nutrient perturbations 116 , as well as varying trace metal 117 , Ca 2+ , Mg 2+ and bisphosphonates 118 , 119 concentrations) have demonstrated their negative impacts on calcification. Coccolithophores are known for having species-specific physiological requirements for calcification, although most studies have focused on E. huxleyi 120 , 121 .…”

Day length as a key factor moderating the response of coccolithophore growth to elevated pCO2

“…For example, 20°C is below the growth optimum (25°C) for G. oceanica (Rhodes et al ; Buitenhuis et al ). Elevated temperatures have also been reported to decrease PIC per cell in coccolithophores (Langer et al ; Feng et al ) and sometimes cause malformation in coccoliths (Gerecht et al ), although this is not consistent across studies (Feng et al ; Sett et al ). High irradiances may cause greater sensitivity to CO 2 (e.g., G. oceanica ), and can shift the CO 2 optima for growth, calcification, and photosynthesis to lower concentrations (Zhang et al ).…”

A 15-million-year-long record of phenotypic evolution in the heavily calcified coccolithophore <i>Helicosphaera</i> and its biogeochemical implications

“…These physiological rates cannot be directly measured in the fossil record. Nevertheless, within a theoretical framework of the relationships between cell geometry, coccolith dimensions and coccolith coverage, cellular levels of organic and inorganic carbon (calcite) quotas can still be estimated with a range of approaches (Bolton et al, 2016;Gibbs et al, 2013Gibbs et al, , 2018Henderiks, 2008;Jin et al, 2018;McClelland et al, 2016).…”

“…is well established based on fossilized coccospheres, representing multiple genotypes and thousands of generations on geological timescales (Gibbs et al, 2018;Henderiks, 2008). Likewise, a positive correlation of coccolith size and cell size in Coccolithus pelagicus is evident when different genotypes from field communities and culture experiments are pooled together (Gibbs et al, 2013).…”

“…Deep-sea sediments hold a ∼ 200 Myr long fossil record of coccoliths (Bown et al, 2004). Some morphometric features of coccoliths, such as length and thickness, correlate with biogeochemically relevant traits: cell size (Henderiks, 2008), growth rates (Gibbs et al, 2013) and the production rates of PIC and POC (Bolton et al, 2016;McClelland et al, 2016). Combined with morphospecies diversity and community composition that is readily inferred from the fossil record (Bown et al, 2004;Knappertsbusch, 2000;Suchéras-Marx and Henderiks, 2014), coccolith morphometry could therefore help elucidate evolutionary processes from the cellular to the community level.…”