Sj. Hird et Sj. Rowland, AN INVESTIGATION OF THE SOURCES AND SEASONAL-VARIATIONS OF HIGHLY BRANCHED ISOPRENOID HYDROCARBONS IN INTERTIDAL SEDIMENTS OF THE TAMAR ESTUARY, UK, Marine environmental research, 40(4), 1995, pp. 423-437
The concentrations and distributions of highly branched isoprenoid (HB
I) hydrocarbons in the surficial sediments of an intertidal mudflat in
the Tamar Estuary, UK, were examined at monthly intervals throughout
1990. C-20 and C-25 HBIs were present all the year round and their con
centrations covaried, maximising at several times in the year, notably
in April-June. Since C-25 HBIs are known to be produced by a species
of diatom (Haslea ostrearia) in culture, it seemed likely that the sed
imentary maxima were also due to production from sediment diatoms. It
was interesting therefore that the April-June HBI maximum did not coin
cide with the (August) maximum concentration of the common diatom hydr
ocarbon n-heneicosahexaene (HE), even though HE is also produced by th
e diatom species which produces C-25 HBIs in culture. Diatoms isolated
om the sediments in August produced abundant HE and only a small prop
ortion of C-25 HBIs. These results suggest that HBI and HE production
maximise at different diatom growth stages, or that the major sources
of HBIs in the sediments ave as yet unidentified diatom species. The d
iatoms isolated from the sediment did not produce C-20 HBIs and to dat
e no organism has produced these in culture. Nonetheless, the delta(13
)C values of the sedimentary C-20 HBIs were consistent with an algal s
ource.