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.
Nutrient supply controls the linkage between species abundance and ecological interactions in marine bacterial communities
