Biometry of detached Emiliania huxleyi coccoliths along the Patagonian Shelf

The biometry (morphology, size) of coccoliths of the coccolithophorid Emiliania huxleyi has implications for their calcite content and cellular rates of calcification. We investigated the biometry of detached coccoliths of E. huxleyi in surface waters during the December 2008 ‘Coccolithophores of the Patagonian Shelf (COPAS’08)’ expedition. Two morphotypes of E. huxleyi were abundant along the shelf, although with different distributions: Morphotype A dominated waters on the shelf and at the northern end of the shelf, while Morphotype B/C dominated offshore and within the main coccolithophore bloom. The 2 morphotypes had opposite relationships to environmental variables along the shelf: Morphotype B/C was abundant in cold (<10°C), nutrient-rich (>10 μmol nitrate kg−1) waters with calcite saturation states of ~3.5, whereas Morphotype A was abundant in warm (>10°C), nutrientpoor 0.1 to 10 μmol nitrate kg−1) waters with higher >4.5) calcite saturation states. These findings support previous suggestions that E. huxleyi morphotypes are distinct ecotypes. Furthermore, we suggest that Morphotype B/C is a Southern Ocean ecotype. Measurements of coccolith distal shield length (total range: 1.8 to 4.4 μm) indicated considerable physiological and/or phenotypic variability along the shelf and within each morphotype. Conversion of distal shield length into estimates of coccolith calcite showed that the E. huxleyi population was producing coccoliths with low median calcite quotas (overall average ± SD, 0.015 ± 0.006 pmol C) relative to other studies of field populations.