Abundances and morphotypes of the coccolithophore <i>Emiliania huxleyi</i> in southern Patagonia compared to neighbouring oceans and Northern Hemisphere fjords

Abstract

Abstract. Coccolithophores are potentially affected by ongoing ocean acidification, where rising CO2 lowers seawater pH and calcite saturation state (Ωcal). Southern Patagonian fjords and channels provide natural laboratories for studying these issues due to high variability in physical and chemical conditions. We surveyed coccolithophore assemblages in Patagonian fjords during late spring 2015 and early spring 2017. Surface Ωcal exhibited large variations driven mostly by freshwater inputs. High-Ωcal conditions (max. 3.6) occurred in the Archipelago Madre de Dios. Ωcal ranged from 2.0–2.6 in the western Strait of Magellan and 1.5–2.2 in the inner channel and was subsaturating (0.5) in Skyring Sound. Emiliania huxleyi was the only coccolithophore widely distributed in Patagonian fjords (> 96 % of total coccolithophores), only disappearing in the Skyring Sound, a semi-closed mesohaline system. Correspondence analysis associated higher E. huxleyi biomasses with lower diatom biomasses. The highest E. huxleyi abundances in Patagonia were in the lower range of those reported in Norwegian fjords. Predominant morphotypes were distinct from those previously documented in nearby oceans but similar to those of Norwegian fjords. Moderately calcified forms of E. huxleyi A morphotype were uniformly distributed throughout Patagonia fjords. The exceptional R/hyper-calcified coccoliths, associated with low Ωcal values in Chilean and Peruvian coastal upwellings, were a minor component associated with high Ωcal levels in Patagonia. Outlying mean index (OMI) niche analysis suggested that pH and Ωcal conditions explained most variation in the realized niches of E. huxleyi morphotypes. The moderately calcified A morphotype exhibited the widest niche breadth (generalist), while the R/hyper-calcified morphotype exhibited a more restricted realized niche (specialist). Nevertheless, when considering an expanded sampling domain, including nearby southeast Pacific coastal and offshore waters, even the R/hyper-calcified morphotype exhibited a higher niche breadth than other closely phylogenetically related coccolithophore species. The occurrence of E. huxleyi in naturally low pH–Ωcal environments indicates that its ecological response is plastic and capable of adaptation.

Transport‐Limited Growth of Coccolith Crystals

“…2) The morphological trait of separated rods is variable among different E. huxleyi strains. [34][35][36][37] In some E. huxleyi strains no gaps are present within the shields, while in others, gaps appear in both shields (Figure 5B,C; Figure S6, Supporting Information). This suggests that the biological control over this trait is indirect and can be executed by controlling the growth regime.…”

Scanning electron microscope analysis of Emiliania huxleyi samples revealed the presence of a single morphotype in the Dardanelles Strait, Turkey

“…The morphotypes can be genotypes or/and ecotypes (Medlin et al, 1996, Iglesias-Rodriquez et al, 2006, Cook et al, 2011, Read et al, 2013. The relative abundance of each type varies along the gradients of environmental factors, most notably temperature, pH, salinity and nutrients which reflected in the global biogeography of different morphotypes (ex., Hagino et al, 2005, Henderiks et al, 2012, Malinverno et al, 2016, Poulton et al, 2011, Díaz-Rosas et al, 2021 with significant biogeochemical consequences (Rigual-Hernandez et al, 2020). Data on the distribution of E. huxleyi and identification of morphotype composition of its populations from different marine environments contribute to the scientific understanding of its distributional patterns and ecological niche (Tyrrell et al, 2008) also help to predict its contribution to downward carbon transport under variations of relevant environmental factors.…”