Temperature affects the morphology and calcification of &amp;lt;i&amp;gt;Emiliania huxleyi&amp;lt;/i&amp;gt; strains

Anaid Rosas-Navarro,Gerald Langer,Patrizia Ziveri

doi:10.5194/bg-13-2913-2016

Abstract

Abstract. The global warming debate has sparked an unprecedented interest in temperature effects on coccolithophores. The calcification response to temperature changes reported in the literature, however, is ambiguous. The two main sources of this ambiguity are putatively differences in experimental setup and strain specificity. In this study we therefore compare three strains isolated in the North Pacific under identical experimental conditions. Three strains of Emiliania huxleyi type A were grown under non-limiting nutrient and light conditions, at 10, 15, 20 and 25 °C. All three strains displayed similar growth rate versus temperature relationships, with an optimum at 20–25 °C. Elemental production (particulate inorganic carbon (PIC), particulate organic carbon (POC), total particulate nitrogen (TPN)), coccolith mass, coccolith size, and width of the tube element cycle were positively correlated with temperature over the sub-optimum to optimum temperature range. The correlation between PIC production and coccolith mass/size supports the notion that coccolith mass can be used as a proxy for PIC production in sediment samples. Increasing PIC production was significantly positively correlated with the percentage of incomplete coccoliths in one strain only. Generally, coccoliths were heavier when PIC production was higher. This shows that incompleteness of coccoliths is not due to time shortage at high PIC production. Sub-optimal growth temperatures lead to an increase in the percentage of malformed coccoliths in a strain-specific fashion. Since in total only six strains have been tested thus far, it is presently difficult to say whether sub-optimal temperature is an important factor causing malformations in the field. The most important parameter in biogeochemical terms, the PIC : POC ratio, shows a minimum at optimum growth temperature in all investigated strains. This clarifies the ambiguous picture featuring in the literature, i.e. discrepancies between PIC : POC–temperature relationships reported in different studies using different strains and different experimental setups. In summary, global warming might cause a decline in coccolithophore's PIC contribution to the rain ratio, as well as improved fitness in some genotypes due to fewer coccolith malformations.

Highlights

When RCC1710 and RCC1252 were analysed together, changes in growth rate only depended significantly on temperature; the carbonate system variables (Table 2) did not much increase the coefficient of determination and none of them were significantly useful in predicting growth rate when used together with temperature (t statistics: p > 0.05)
Since the positive correlation between coccolith mass and particulate inorganic carbon (PIC) production was observed in response to seawater carbonate chemistry changes as well (Bach et al, 2012), it can be hypothesized that coccolith mass might be a good proxy for PIC production independent of the environmental parameter causing the change in PIC production
Since the effect of sub-optimal temperature on coccolith morphogenesis is strain-specific, a statistically relevant number of strains have to be tested in order to clarify whether this effect is ecologically relevant

Summary

Introduction

Emiliania huxleyi (Lohmann) Hay and Mohler is a cosmopolitan (McIntyre and Bé, 1967; Brown, 1995), genetically diverse (Medlin et al, 1996; Schroeder et al, 2005; Iglesias-Rodríguez et al, 2006; Hagino et al, 2011; Read et al, 2013), morphologically variable (Hagino et al, 2005; Hagino and Okada, 2006; Cubillos et al, 2007) marine photosynthetic and calcifying (Brownlee and Taylor, 2004) unicellular haptophyte algae species and the most abundant of the coccolithophores. Rosas-Navarro et al.: Temperature affects the morphology and calcification of E. huxleyi

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Discussion

Conclusion