Phytoplankton distribution during two contrasted summers in a Mediterranean harbour: combining automated submersible flow cytometry with conventional techniques.

Automated in situ flow cytometry, high-pressure liquid chromatography (HPLC), optical microscopy and fluorometry were combined to monitor phytoplankton over two summer periods (2005 and 2006). In 2006, temperature was higher and nutrients lower than in 2005, generating differences in the phytoplankton assemblages (i.e.

Comparative study of three analysis methods (TTGE, flow cytometry and HPLC) for xenobiotic impact assessment on phytoplankton communities.

The impacts of the fungicide Opus (epoxiconazole) on marine phytoplankton communities were assessed in a 12-day field experiment using in situ microcosms maintained underwater at 6 m depth. Three community analysis methods were compared for their sensitivity threshold in fungicide impact detection. When phytoplankton communities were exposed to 1 microg l(-1) of epoxiconazole, no effects could be demonstrated using TTGE (Temporal Temperature Gradient gel Electrophoresis), flow cytometry or HPLC.

Regiospecific oxygenation of alkenones in the benthic haptophyte Chrysotila lamellosa Anand HAP 17.

Two groups of previously unidentified C37-C39 epoxyalkenones and alkenediones were detected in late stationary phase cultures of the haptophyte microalga Chrysotila lamellosa. The formation of these compounds is attributed to the involvement of enzymatic processes acting specifically on the C-21 or C-22 allylic carbon and the omega15 double bond of methyl and ethyl alkenones respectively. Thus, the epoxyalkenones appear to be derivatives of alkenones where the omega15 double bond is oxidized to the epoxide.

C(25) highly branched isoprenoid alkenes from the marine benthic diatom Pleurosigma strigosum.

The hydrocarbon composition of the marine diatom Pleurosigma strigosum isolated from coastal Mediterranean sediments is described. A suite of five C(25) highly branched isoprenoid (HBI) alkenes with 2-5 double bonds were detected together with n-C(21:4) and n-C(21:5) alkenes and squalene. The analysis by (1)H and (13)C NMR spectroscopy of two isolated HBI alkenes allowed the structural identification of a novel C(25) HBI triene (2,6,10,14-tetramethyl-7-(3-methylpent-4-enyl)-pentadeca-5E,13-diene) and the first identification in diatom cells of 2,6,10,14-tetramethyl-7-(3-methylpent-4-enyl)-pentadec-5E-ene, an HBI previously detected in marine sediments and particulate matter.

Long-chain alkenones and related compounds in the benthic haptophyte Chrysotila lamellosa Anand HAP 17.

The neutral lipid compositions of the coastal haptophyte Chrysotila lamellosa HAP 17 grown in batch culture at 10 and 20 degrees C have been determined. A comparison was also made between the lipid compositions of cells harvested in early and late stationary phase. This species contains a suite of very long-chain C(37)-C(40) alkenones and alkenoates as found in a few microalgae from the Haptophyta.

On the origin of cis-vaccenic acid photodegradation products in the marine environment.

The origin of 11-hydroxyoctadec-trans-12-enoic and 12-hydroxyoctadec-trans-10-enoic acids (photodegradation products of cis-vaccenic acid) in the marine environment was investigated. cis-Vaccenic acid is commonly used as a bacterial biomarker; however, in heterotrophic bacteria the observed rates of cis-vaccenic acid photodegradation are negligible. Here, two hypotheses explaining the source of the photoproducts were tested.

A flow cytometric approach to assess phytoplankton respiration.

Microbial respiration in the ocean is considered as the major process representative of the organic matter biological oxidation. The corresponding metabolic CO2 production was estimated to be about 22 Pg C y(-1). However, the in situ respiration rate is generally too low (by several orders of magnitude) to be accessible to the available direct measurement methods.