Day length as a key factor moderating the response of coccolithophore growth to elevated p CO 2

• Published in: Limnology and Oceanography
• Main Authors: Bretherton, Laura, Poulton, Alex J., Lawson, Tracy, Rukminasari, Nita, Balestreri, Cecilia, Schroeder, Declan, Mark Moore, C., Suggett, David J.
• Other Authors: Australian Research Council, Natural Environment Research Council
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 2019
• Subjects: Ocean acidification
• Online Access: http://dx.doi.org/10.1002/lno.11115; https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1002%2Flno.11115; https://onlinelibrary.wiley.com/doi/pdf/10.1002/lno.11115; https://onlinelibrary.wiley.com/doi/full-xml/10.1002/lno.11115; https://onlinelibrary.wiley.com/doi/am-pdf/10.1002%2Flno.11115; https://aslopubs.onlinelibrary.wiley.com/doi/pdf/10.1002/lno.11115

Abstract The 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 p CO 2 with the light : dark (L : D) cycle. We confirmed a general regulatory effect of photoperiod on the p CO 2 response, whereby growth and particulate inorganic carbon and particulate organic carbon (PIC : POC) ratios were reduced with elevated p CO 2 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 p CO 2 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 p CO 2 ‐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.