Table 1.
List of Emiliania huxleyi strains cultured in this study.
Fig 1.
Growth rates of of six strains of E. huxleyi under three salinity conditions.
(A) Exponential growth rates (mean and standard deviation, n = 3 for strains PLYB11, RCC1232, RCC1824 and RCC904; n = 1 for strains RCC1210 and RCC868) at salinity 25 (yellow), 35 (green) and 45 (blue). Detail of cell density with experiment day under each salinity condition for the two focal strains in this study: (B) strain PLYB11 and (C) strain RCC1232. Each data point represents the mean and standard deviation (bars) of cell counts from triplicate flasks. Lines (solid colour) show the exponential growth curve of each experiment fitted to exponential days of growth to indicate the point at which cultures stopped growing exponentially (days of non-exponential growth, dashed lines in C represent hypothetical continuation of exponential growth). The arrows indicate the day on which samples were taken for morphological analysis, with arrow colour corresponding to salinity treatment. See S1 Table for exponential growth rate data for each strain.
Table 2.
Mean coccolith morphometry and coccosphere size, cell density at time of sampling, and growth rate in Emiliania huxleyi strains PLYB11 and RCC1232 grown at salinities of 25, 35, and 45.
Fig 2.
Illustrative coccosphere (top) and coccolith (bottom) of E. huxleyi. (A) strain PLYB11 and (B) strain RCC1232. Distinctive morphological features of each strain are highlighted and measurements of coccosphere diameter (Ø), coccolith length (CL) and coccolith width (CW) referred to in this study are defined. The scale bar represents 1 μm in all instances. All images are from salinity 35 treatment.
Fig 3.
Coccolith and coccosphere morphology of strain PLYB11 (green, circle) and strain RCC1232 (blue, square) grown at control salinity 35. (A) Coccolith length (0.25 μm bin size) and (B) coccosphere diameter (0.5 μm bin size). Descriptive statistics (median, 10th, 25th, 75th, 90th percentiles) of the data for each strain are presented above each histogram as box-and-whisker plots.
Fig 4.
Emiliania huxleyi coccolith and coccosphere morphology under salinity conditions 25, 35 and 45.
(A) Coccolith length, (B) coccolith surface area, (C) coccosphere diameter of E. huxleyi strains PLYB11 and RCC1232. Coccosphere diameter could not be measured in strain RCC1232 at salinity 25. Violin plots show the full range of morphological data with white 25th to 75th percentiles overlain. The central black line represents the median of the data. The mean, standard deviation and n of data are reported in Table 2 and full data in S2 Table.
Fig 5.
Representative E. huxleyi coccosphere morphology under each salinity treatment.
Strain RCC1232 grown under (A) salinity 25, (B) salinity 35, and (C) salinity 45. Strain PLYB11 grown under (D) salinity 25, (E) salinity 35, and (F) salinity 45. All images are at the same scale, scale bar represents 1 μm.
Fig 6.
Comparison of coccolith size response (percentage change) across E. huxleyi strains under experimental high and low salinity conditions.
(A) Percentage change in CL under a salinity decrease from 35 to ~25, and (B) salinity increase from 35 to ~45 from strains PLYB11 and RCC1232 in this study (black stripe-fill bars) compared to results for a range of strains compiled from published literature (referenced by superscript letters: a. [17], b. [19], c. [18], d. [20], e. [6]). Strains have been numbered and are grouped respective to the salinity characteristics of their respective isolation locations, which are shown on map (C)–strain 1. MR70N, 2. RCC868, 3. DW53/74/6, 4. G177aGa, 5. PLYB11/PLYB92/11, 6. SC91, 7. RCC1210, 8. SAG33.90, 9. RCC1232, 10. RCC1843, 11. RCC1824. Where no high salinity experiments were undertaken for the strain, an ‘x’ is shown. Where the direction of CL changes is opposite to the majority trend (i.e., a percentage increase in CL where all other strains showed a percentage decrease in CL), the data bar is outlined without fill. The dashed vertical line in (A) and (B) denotes the 5% decrease or increase in CL, respectively, for guidance. The ‘*’ for the data PLYB11 from [19] indicates that the high salinity treatment in this study was at 41 rather than 45.