A review of sterol markers for marine and terrigenous organic matter

Fatty acids have been used as qualitative markers to trace or confirm predator-prey relationships in the marine environment for more than thirty years. More recently, they have also been used to identify key processes impacting the dynamics of some of the world's major ecosystems. The fatty acid trophic marker (FATM) concept is based on the observation that marine primary producers lay down certain fatty acid patterns that may be transferred conservatively to, and hence can be recognized in, primary consumers. To identify these fatty acid patterns the literature was surveyed and a partial least squares (PLS) regression analysis of the data was performed, validating the specificity of particular microalgal FATM. Microalgal group specific FATM have been traced in various primary consumers, particularly in herbivorous calanoid copepods, which accumulate large lipid reserves, and which dominate the zooplankton biomass in high latitude ecosystems. At higher trophic levels these markers of herbivory are obscured as the degree of carnivory increases, and as the fatty acids originate from a variety of dietary sources. Such differences are highlighted in a PLS regression analysis of fatty acid and fatty alcohol compositional data (the components of wax esters accumulated by many marine organisms) of key Arctic and Antarctic herbivorous, omnivorous and carnivorous copepod species. The analysis emphasizes how calanoid copepods separate from other copepods not only by their content of microalgal group specific FATM, but also by their large content of long-chain monounsaturated fatty acids and alcohols. These monounsaturates have been used to trace and resolve food web relationships in, for example, hyperiid amphipods, euphausiids and fish, which may consume large numbers of calanoid copepods. Results like these are extremely valuable for enabling the discrimination of specific prey species utilized by higher trophic level omnivores and carnivores without the employment of invasive techniques, and thereby for identifying the sources of energetic reserves. A conceptual model of the spatial and temporal dominance of group-specific primary producers, and hence the basic fatty acid patterns available to higher trophic levels is presented. The model is based on stratification, which acts on phytoplankton group dominance through the availability of light and nutrients. It predicts the seasonal and ecosystem specific contribution of diatom and flagellate/microbial loop FATM to food webs as a function of water column stability. Future prospects for the application of FATM in resolving dynamic ecosystem processes are assessed.

Fatty acid trophic markers in the pelagic marine environment.

Microalgal biomarkers: A review of recent research developments

Phospholipid, ester-linked fatty acid profiles showed changes in benthic prokaryotic community structure reflecting culture manipulations that were both quantitative and statistically significant. Fatty acid structures, including the position and cis/ trans geometry of double bonds, were chemically verified by GC/MS after appropriate derivatization. The fatty acid profiles of independent flasks showed reproducible shifts when manipulated identically and significant differences when manipulated with different treatments. The absence of polyunsaturated fatty acids indicated that the consortia were predominantly prokaryotic. The prokaryotic consortia of different treatments could be differentiated by the proportions of cyclopropyl fatty acids and the proportions and geometry of monounsaturated fatty acids.

Phospholipid, ester-linked fatty acid profiles as reproducible assays for changes in prokaryotic community structure of estuarine sediments

Comparative organic geochemistries of soils and marine sediments

Microbial lipids of an intertidal sediment—I. Fatty acids and hydrocarbons

A comparison of lipid components of the fresh and dead leaves and pneumatophores of the mangrove Avicennia marina

Early diagenesis of phytyl esters in a contemporary temperate intertidal sediment

A sedimentary bacterial isolate has been shown to contain trans-monounsaturated fatty acids (6% of the total fatty acids) The ratio of trans- to cis-acids in this isolate was in the range 32 to 76 The identification of trans-monounsaturated acids in a marine bacterium implied that the trans-acids which have been reported in recent sediments could derive, in whole or part, from direct bacterial input

trans-Monounsaturated Acids in a Marine Bacterial Isolate.

A study of the processes operating upon organic molecules in present day sediments can illuminate kerogen-petroleum inter-relationships. The starting point for kerogen formation is not the initial biological inputs to a sediment but rather those organic molecules which survive the active upper 1 to 2 cm of surface sediment where biological diagenesis is most marked. Depth profile studies on fatty acids, alcohols, sterols, and dicarboxylic acids emphasise the differing sensitivity of lipid classes to chemical and biological processes. Distribution patterns for these lipids in older sediments thus reflect the changed weightings which result from utilisation and preservation within the biologically active zone. Environmental effects are discussed in terms of stability of chlorophyll-a and bacteriochlorophyll-a molecules in sediments taken from temperate zones and contrasted with those in sediments from tropical zones. Whilst demetallation is an important degradative pathway for bacteriochlorophyll-a, this is not the case for chlorophyll-a. In this latter molecule the pigment ring system is chemically unstable, but the phytyl ester appears to remain substantially unhydrolysed. The data given in the tables bear on alkane genesis and on the origin of the isoprenoid alkane biological markers. The consequences of this type of study for side chain structures in the coal macromolecule and industrial conversion processes are noted.

F.T. Gillan

Papers

Microbial lipids of an intertidal sediment—I. Fatty acids and hydrocarbons

A comparison of lipid components of the fresh and dead leaves and pneumatophores of the mangrove Avicennia marina

Early diagenesis of phytyl esters in a contemporary temperate intertidal sediment

trans-Monounsaturated Acids in a Marine Bacterial Isolate.

Kerogen precursors: chemical and biological alteration of lipids in the sedimentary surface layer