Full annual monitoring of Subantarctic Emiliania huxleyi populations reveals highly calcified morphotypes in high-CO2 winter conditions

Abstract

Ocean acidification is expected to have detrimental consequences for the most abundant calcifying phytoplankton species Emiliania huxleyi. However, this assumption is mainly based on laboratory manipulations that are unable to reproduce the complexity of natural ecosystems. Here, E. huxleyi coccolith assemblages collected over a year by an autonomous water sampler and sediment traps in the Subantarctic Zone were analysed. The combination of taxonomic and morphometric analyses together with in situ measurements of surface-water properties allowed us to monitor, with unprecedented detail, the seasonal cycle of E. huxleyi at two Subantarctic stations. E. huxleyi subantarctic assemblages were composed of a mixture of, at least, four different morphotypes. Heavier morphotypes exhibited their maximum relative abundances during winter, coinciding with peak annual TCO 2 and nutrient concentrations, while lighter morphotypes dominated during summer, coinciding with lowest TCO 2 and nutrients levels. The similar seasonality observed in both time-series suggests that it may be a circumpolar feature of the Subantarctic zone. Our results challenge the view that ocean acidification will necessarily lead to a replacement of heavily-calcified coccolithophores by lightly-calcified ones in subpolar ecosystems, and emphasize the need to consider the cumulative effect of multiple stressors on the probable succession of morphotypes.

Planktonic protist diversity across contrasting Subtropical and Subantarctic waters of the southwest Pacific

“…Gephyrocapsa oceanica was the most prevalent and abundant coccolithophore species found in our study. ASVs assigned ot this species were found across all water masses but tended to be most abundant in the STF (Figure S9; Figure S10) in agreement with previous microscopy-based studies in this region of the SW Pacific (Rigual-Hernández et al 2020; Saavedra-Pellitero et al 2014). Emiliania huxleyii , which generally dominate coccolithophore assemblages in this region (Chang and Northcote 2016; Saavedra-Pellitero et al 2014), and in the Southern Ocean (Balch et al 2016; Holligan et al 2010) showed very low abundances across the different water masses surveyed in this study (data not shown).…”

Shell density of planktonic foraminifera and pteropod species Limacina helicina in the Barents Sea: Relation to ontogeny and water chemistry

“…helicina and ongoing thickening means that they can choose specific areas of their shell to thicken after the initial calcification as part of a resilience strategy to environmental stress. Instances of over-calcification as a reaction to low Ω values have been found in barnacles [ 103 ] and coccolithophores [ 104 , 105 ], further suggesting that some calcifiers can re-direct energy for calcification when their shells are vulnerable. However, a study from an upwelling area in the northern California Current Ecosystem suggests that L .…”

Coccolithophore biodiversity controls carbonate export in the Southern Ocean

“…For the birefringence-based approach, a minimum of 50 coccoliths of each of the main coccolithophore species were imaged using a Nikon Eclipse LV100 POL light microscope equipped with circular polarization and a digital camera (Nikon DS-Fi1 8 bit colour). The only exception was E. huxleyi, for which coccolith mass values had already been estimated in all the same samples at high resolution by Rigual-Hernández et al (2020). For the minor components of the flux assemblage, a lower number of coccoliths were measured (Table 1).…”