Abstract
Coccolithophores are unicellular marine phytoplankton and important contributors to global carbon cycling. Most work on coccolithophore sensitivity to climate change has been on the small, abundant bloom-forming species Emiliania huxleyi and Gephyrocapsa oceanica. However, large coccolithophore species can be major contributors to coccolithophore community production even in low abundances. Here we fit an analytical equation, accounting for simultaneous changes in CO2 and light intensity, to rates of photosynthesis, calcification and growth in Scyphosphaera apsteinii. Comparison of responses to G. oceanica and E. huxleyi revealed S. apsteinii is a low-light adapted species and, in contrast, becomes more sensitive to changing environmental conditions when exposed to unfavourable CO2 or light. Additionally, all three species decreased their light requirement for optimal growth as CO2 levels increased. Our analysis suggests that this is driven by a drop in maximum rates and, in G. oceanica, increased substrate uptake efficiency. Increasing light intensity resulted in a higher proportion of muroliths (plate-shaped) to lopadoliths (vase shaped) and liths became richer in calcium carbonate as calcification rates increased. Light and CO2 driven changes in response sensitivity and maximum rates are likely to considerably alter coccolithophore community structure and productivity under future climate conditions.
Highlights
Coccolithophores are a group of phytoplankton, which produce both particulate organic carbon through photosynthesis and particulate inorganic carbon through calcification[1,2]
Depending upon CO2 level and light intensity, rates varied between 28–234 pg C cell−1 d−1 for calcification, 60–243 pg C cell−1 d−1 for photosynthesis and 0.14–0.57 d−1 for growth (Table S1)
Particulate inorganic to organic carbon ratios particulate inorganic carbon (PIC):particulate organic carbon (POC) ratios increased with CO2 to an optimal point before declining with further increases in CO2 (Table S1)
Summary
Coccolithophores are a group of phytoplankton (division Haptophyta, class Prymnesiophyceae), which produce both particulate organic carbon through photosynthesis and particulate inorganic carbon through calcification[1,2]. Of approximately 200 extant species of coccolithophores (e.g.21), the majority of research into coccolithophore responses to climate change come from only a few species such as Emiliania huxleyi, Gephyrocapsa oceanica, Calcidiscus leptoporus, and Coccolithus pelagicus spp. braarudii Of these most studies have been on E. huxleyi which is considered a keystone species due to its ability to form massive blooms[22], its dominance within the coccolithophore assemblage[3,6,23], and its almost global distribution[3] (North and South Atlantic),[22] (North Atlantic),[6] (Equatorial and sub-equatorial Pacific),[24] (East Mediterranean),[25,26] (Southern Ocean),[27] (North Sea). As such the aim of this study was to examine the effects of changing carbonate chemistry and light intensity on the large coccolithophore S. apsteinii
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