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

Laura Bretherton,Tracy Lawson,David J Suggett,C Mark Moore,Nita Rukminasari,Cecilia Balestreri,Declan Schroeder,Alex J Poulton

doi:10.1002/lno.11115

Abstract

AbstractThe fate of coccolithophores in the future oceans remains uncertain, in part due to key factors having not been standardized across experiments. A potentially moderating role for differences in day length (photoperiod) remains largely unexplored. We therefore cultured four different geographical isolates of the species Emiliania huxleyi, as well as two additional species, Gephyrocapsa oceanica (tropical) and Coccolithus braarudii (temperate), to test for interactive effects of pCO2 with the light : dark (L : D) cycle. We confirmed a general regulatory effect of photoperiod on the pCO2 response, whereby growth and particulate inorganic carbon and particulate organic carbon (PIC : POC) ratios were reduced with elevated pCO2 under 14 : 10 h L : D, but these reductions were dampened under continuous (24 h) light. The dynamics underpinning this pattern generally differed for the temperate vs. tropical isolates. Reductions in PIC : POC with elevated pCO2 for tropical taxa were largely through reduced calcification and enhanced photosynthesis under 14 : 10 h L : D, with differences dampened under continuous light. In contrast, reduced PIC : POC for temperate strains reflected increases of photosynthesis that outpaced increases in calcification rates under 14 : 10 h L : D, with both responses again dampened under continuous light. A multivariate analysis of 35 past studies of E. huxleyi further demonstrated that differences in photoperiod account for as much as 40% (strain B11/92) to 55% (strain NZEH) of the variance in reported pCO2‐induced reductions to growth but not PIC : POC. Our study thus highlights a critical role for day length in moderating the effect of ocean acidification on coccolithophore growth and consequently how this response may play out across latitudes and seasons in future oceans.

Highlights

Y aPresent address: Environmental Science Department, Mount Allison University, Sackville, New Brunswick, Canada bPresent address: Strada Campagnola, Acquanegra sul Chiese (MN), Italy cPresent address: Veterinary Population Medicine, College of Veterinary Medicine, University of Minnesota, St Paul, Minnesota
Coccolithophores appear susceptible to ocean acidification (OA), the process whereby rising atmospheric pCO2 concentrations are resulting in lower ocean pH and modifications to carbonate chemistry
Media in ambient CO2 cultures was more stable, with AT only drifting by 2% to 7% below that expected (~ 2400 μmol kg−1), whereas the high CO2 cultures typically fell below 2000 μmol kg−1

Summary

Introduction

Y aPresent address: Environmental Science Department, Mount Allison University, Sackville, New Brunswick, Canada bPresent address: Strada Campagnola, Acquanegra sul Chiese (MN), Italy cPresent address: Veterinary Population Medicine, College of Veterinary Medicine, University of Minnesota, St Paul, Minnesota. Coccolithophores appear susceptible to ocean acidification (OA), the process whereby rising atmospheric pCO2 concentrations are resulting in lower ocean pH and modifications to carbonate chemistry (see Meyer and Riebesell, 2015). Coccolithophore responses may be strain-specific (Langer et al 2009) and dependent upon environmental history and local adaptation (Lohbeck et al 2012)

Methods

Results

Conclusion