•E. huxleyi NIES837 and G. oceanica NIES1315 produces abundantly nonacosadienes.•Double bond positions in C29 alkenes were determined by MS of their DMDS adducts.•The most abundant C29 alkene isomer was determined as 2,20-nonacosadiene.•Nonacosadienes have potential for being distinct haptophyte biomarkers.The hydrocarbons in cultures of marine haptophytes Emiliania huxleyi NIES837 and Gephyrocapsa oceanica NIES1315 were analyzed, and nonacosadienes and hentriacontadienes were detected as the major compounds in both strains. C29 and C31 monoenes and di-, tri- and tetra-unsaturated C33 alkenes were also detected as minor compounds but not C37 and C38 alkenes. The positions of the double bonds in the C29 and C31 alkenes were determined by mass spectrometry of their dimethyl disulfide (DMDS) adducts. Among the four C29 alkenes identified, the most abundant isomer was 2,20-nonacosadiene, and the other three compounds were 1,20-nonacosadiene, 3,20-nonacosadiene and 9-nonacosene, respectively. Hitherto, 2,20-nonacosadiene and 3,20-nonacosadiene were unknown to be natural products. The double bond at the n-9 (ω9) position in these C29 alkenes is hypothesized to be derived from precursors of unsaturated fatty acids possessing an n-9 double bond, such as (9Z)-9-octadecenoic acid. Nonacosadienes have the potential for being used as distinct haptophyte biomarkers.Cultured Emiliania huxleyi NIES837 and Gephyrocapsa oceanica NIES1315 abundantly produce C29 alkenes, including 2,20-nonacosadiene and 3,20-nonacosadiene identified.

•Cultured Chrysotila lamellosa CCMP1307 produced high proportion of C37:4 alkenones.•C. lamellosa  U37K values reproduced the typical values for C37:4-rich lakes.•U37K calibration showed a better fit with temperature than U37K′ calibration.•The unsaturation degree of C31 alkenes was also controlled by growth temperature.The compositions of long chain alkenes, alkenones and alkenoates in a cultured strain of the haptophyte Chrysotila lamellosa CCMP1307, isolated from a salt marsh, were investigated. The biomarker patterns were distinctive and showed a high proportion of tetraunsaturated alkenones and alkenoates, with a pronounced proportion of C40 alkenones and a lack of C38 methyl and C39 ethyl alkenones. Linear regression of the alkenone unsaturation degree (U37K) with growth temperature (T) was obtained over the range of possible CCMP1307 growth temperature values (4–20 °C): U37K = 0.045 × T (°C) − 1.016, (n = 13, r2 0.96), while the U37K′ values were weakly correlated with T  : U37K′ = 0.0035T (°C) + 0.0511 (n = 18, r2 0.70). The U37K calibration exhibited a low y-intercept in comparison with that of a Chinese inland lake strain reported previously. The data show significant intraspecific variation in U37K for C. lamellosa between strains from different geographic origins. C. lamellosa   CCMP1307 reproduced typical U37K values observed in C37:4 rich lakes, especially at lower temperature (< 15 °C). In addition, we identified C29:2, C31:1, C31:2 and C31:3 alkenes, and found that the unsaturation degree of C31 alkenes (U31en), calculated with C31:1 and C31:2 alkenes, might also be a useful index of growth temperature for the haptophyte C. lamellosa.