Variations in distributions of C25 highly branched isoprenoid (HBI) alkenes in the diatom, Haslea ostrearia: influence of salinity

C25 HBI alkenes of the diatom, Haslea ostrearia, have been examined in experiments in which the algae were cultured for up to 10 days at 14–15°C at nine different salinities (15 to 40 per mil). H. ostrearia proved to be an osmotolerant organism and growth was observed at all salinities. After 10 days growth at the lowest and highest salinities of 15 and 40 per mil, the concentrations of 2,10,14-trimethyl-6-methylene-7-(3-methylpent-1-enyl)pentadec-9-ene, which was the only HBI present in any of the samples, averaged 1.2±0.7 and 2.1±0.7 pg cell−1, respectively. These were slightly lower than the HBI concentrations at 25 to 35 per mil (2.8±0.5 pg cell−1). The data indicate that although salinity has an influence on HBI production in H. ostrearia, factors other than salinity are probably more important in controlling the large variations of HBI alkene concentrations and distributions found in sedimentary environments.