Can morphological features of coccolithophores serve as a reliable proxy to reconstruct environmental conditions of the past?

Abstract

Abstract. Morphological changes in coccoliths, tiny calcite platelets covering the outer surface of coccolithophores, can be induced by physiological responses to environmental changes. Coccoliths recovered from sedimentary successions may therefore provide information on paleo-environmental conditions prevailing at the time when the coccolithophores were alive. To calibrate the biomineralization responses of ancient coccolithophore to environmental changes, studies often compared the biological responses of living coccolithophore species with paleo-data from calcareous nannofossils. However, there is uncertainty whether the morphological responses of living coccolithophores are representative of those of the fossilized ancestors. To investigate this, we exposed four living coccolithophore species (Emiliania huxleyi, Gephyrocapsa oceanica, Coccolithus pelagicus subsp. braarudii, and Pleurochrysis carterae) that have been evolutionarily distinct for hundreds of thousands to millions of years, to a range of environmental conditions (i.e., changing light intensity, Mg∕Ca ratio, nutrient availability, temperature, and carbonate chemistry) and evaluated their responses in coccolith morphology (i.e., size, length, width, malformation). The motivation for this study was to test if there is a consistent morphological response of the four species to changes in any of the tested abiotic environmental factors. If this was the case, then this could suggest that coccolith morphology can serve as a paleo-proxy for that specific factor because this response is conserved across species that have been evolutionary distinct over geological timescales. However, we found that the four species responded differently to changing light intensity, Mg∕Ca ratio, nutrient availability, and temperature in terms of coccolith morphology. The lack of a common response reveals the difficulties in using coccolith morphology as a paleo-proxy for these environmental drivers. However, a common response was observed under changing seawater carbonate chemistry (i.e., rising CO2), which consistently induced malformations. This commonality provides some confidence that malformations found in the sedimentary record could be indicative of adverse carbonate chemistry conditions.

Influence of the Calcium Carbonate Shell of Coccolithophores on Ingestion and Growth of a Dinoflagellate Predator

“…In contrast, the specimen of O. marina in Figure 7 egested visually empty coccospheres and therefore seems capable to assimilate the organic material inside the coccosphere. The empty coccospheres shown in Figure 7 may correspond to those flow Faucher and were published previously in a study that compared physiological and morphological characters of four coccolithophore species under different abiotic conditions (Faucher et al, 2020).…”

“…(C) Coccospheres of G. oceanica. The pictures (B,C) were kindly provided by Dr. Giulia Faucher and were published previously in a study that compared physiological and morphological characters of four coccolithophore species under different abiotic conditions(Faucher et al, 2020).…”

Coccolith volume of the Southern Ocean coccolithophore Emiliania huxleyi as a possible indicator for palaeo‐cell volume

“…area, volume, mass and degree of malformation) have been evaluated in regard to environmental parameters with the prospect to enhance the toolbox of coccolithophore‐based palaeo‐proxies for past and current oceanic conditions (e.g. Henderiks and Pagani, 2008; Triantaphyllou et al, 2010; Poulton et al, 2011; Müller et al, 2012; Hoffmann et al, 2015; Faucher et al, 2020). Over the past decade, several studies investigated the allometry of fossil and recent coccolithophores (Henderiks, 2008; Henderiks and Pagani, 2008; Gerecht et al, 2015; Sheward et al, 2017).…”

Strain-specific morphological response of the dominant calcifying phytoplankton species Emiliania huxleyi to salinity change

“…In particular, the morphology of the intricate, individual calcite plates (coccoliths) that form a cell covering (the coccosphere) of coccolithophores have been shown to respond to a range of environmental perturbations in laboratory studies, including temperature [5][6][7][8][9], nutrient limitation [10][11][12], light intensity [11,12], carbonate chemistry [7,[12][13][14][15], trace metals [12], and salinity [6,[16][17][18][19][20]. Plankton populations and fossil assemblages also show variability in coccolith morphology and size spatially and on seasonal to geological timescales that have been linked to changing ocean conditions, e.g., [21][22][23][24][25][26][27][28].…”