Seasonal variations of highly branched isoprenoid hydrocarbons and pigment biomarkers in intertidal sediments of the Tamar Estuary, UK

After preliminary experiments to ensure the reliability of the extraction and sampling methods, the concentrations and distributions of highly branched isoprenoid (HBI) alkenes, n-henicosahexaene (HE), carotenoids and chlorophylls in surficial sediments of intertidal mudflats in the Tamar estuary, UK, were examined, at least monthly and often fortnightly, during the period September 1993 to August 1994. The alkenes and the carotenoid fucoxanthin were present all year round, each exhibiting a trimodal sinuosity and suggesting the same or similar sources, most likely diatoms. Non-coincidence of the HBI, HE and fucoxanthin maxima, each offset from one another by 2–4 weeks, suggested that the HBI distributions offer a means of distinguishing the contribution of diatomaceous HBI producers, such as Haslea spp. from the total diatom populations. Reasons for the lack of reports of Haslea spp. in sediments from microscopy studies are discussed.