Change in coccolith size and morphology due to response to temperature and salinity in coccolithophore <i>Emiliania huxleyi</i> (Haptophyta) isolated from the Bering and Chukchi seas

Abstract

Abstract. Strains of the coccolithophore Emiliania huxleyi (Haptophyta) collected from the subarctic North Pacific and Arctic oceans in 2010 were established as clone cultures and have been maintained in the laboratory at 15 • C and 32 ‰ salinity. To study the physiological responses of coccolith formation to changes in temperature and salinity, growth experiments and morphometric investigations were performed on two strains, namely MR57N isolated from the northern Bering Sea and MR70N at the Chukchi Sea. This is the first report of a detailed morphometric and morphological investigation of Arctic Ocean coccolithophore strains. The specific growth rates at the logarithmic growth phases in both strains markedly increased as temperature was elevated from 5 to 20 • C, although coccolith productivity (estimated as the percentage of calcified cells) was similar at 10-20 % at all temperatures. On the other hand, the specific growth rate of MR70N was affected less by changes in salinity in the range 26-35 ‰, but the proportion of calcified cells decreased at high and low salinities. According to scanning electron microscopy (SEM) observations, coccolith morphotypes can be categorized into Type B/C on the basis of their biometrical parameters. The central area elements of coccoliths varied from thin lath type to well-calcified lath type when temperature was increased or salinity was decreased, and coccolith size decreased simultaneously. Coccolithophore cell size also decreased with increasing temperature, although the variation in cell size was slightly greater at the lower salinity level. This indicates that subarctic and arctic coccolithophore strains can survive in a wide range of seawater temperatures and at lower salinities with change in their morphology. Because all coccolith biometric parameters followed the scaling law, the decrease in coccolith size was caused simply by the reduced calcification. Taken together, our results suggest that calcification productivity may be used to predict future oceanic environmental conditions in the polar regions.

Coccolithophore populations and their contribution to carbonate export during an annual cycle in the Australian sector of the Antarctic zone

“…Firstly, the E. huxleyi coccolithophores living in the Arctic seas most likely correspond to a different ecotype than those dwelling in the AZ waters, and therefore they may potentially exhibit different physiological responses to water temperature changes. Secondly, the SST range in our study site was remarkably lower (0-3 • C) than that used by Saruwatari et al (2016) in their cultures (5-20 • C). These limitations make drawing inferences from Saruwatari et al (2016) difficult.…”

“…Secondly, the SST range in our study site was remarkably lower (0-3 • C) than that used by Saruwatari et al (2016) in their cultures (5-20 • C). These limitations make drawing inferences from Saruwatari et al (2016) difficult. Feng et al (2017, on the other hand, showed that the optimal temperature for calcification of E. huxleyi cells retrieved in the Southern Ocean (morphotype A, strain NIWA1108) was ∼ 20 • C, while temperatures below 10 • C resulted in a dramatic reduction of calcification rates and severe malformations of coccoliths, such as incomplete distal shield elements.…”

“…However, comparison of our results with those of Saruwatari et al (2016) should be done with great caution for two reasons. Firstly, the E. huxleyi coccolithophores living in the Arctic seas most likely correspond to a different ecotype than those dwelling in the AZ waters, and therefore they may potentially exhibit different physiological responses to water temperature changes.…”

“…In terms of temperature effects, Saruwatari et al (2016) described a decrease in coccolith size with increasing temperature by cultivating E. huxleyi strains (morphotype B/C, strains MR57N and MR70N) from the Bering and Chukchi seas. However, comparison of our results with those of Saruwatari et al (2016) should be done with great caution for two reasons.…”

The effect of salinity on the biogeochemistry of the coccolithophores with implications for coccolith-based isotopic proxies

“…8). In particular, it has been found that E. huxleyi and G. oceanica achieved better growth at the lowest salinities, with a lower limit of 25% for the former species (Fisher and Honjo, 1989;Saruwatari et al, 2016;Schouten et al, 2006). Except for Sal29, a salinity at which no growth was achieved by G. oceanica in our batches, our data for this species, and for G. ericsonii, are compatible with this overarching observation that the cells exhibit diminished growth rate with increasing salinity (Fig.…”