Lyngbya Aestuarii Research Articles

Diatoms inhabiting a wind flat of the Baltic Sea: Species diversity and seasonal succession

The seasonal succession of brackish microphytobenthos (consisting of diatoms and cyanobacteria) was studied at a wind flat at the southern Baltic Sea coast. Wind flats are coastal zones with a high degree of exposition becoming flooded irregularly as a function of sea levels, prevailing wind direction and speed. These extreme environmental conditions favour the formation of laminated microbial mats similar to those in tidal flats. Special attention was paid to the comparison of diatom compositions in a laminated microbial mat as a relatively steady biocoenosis, and compositions in sediment without a mat, probably a more disturbed area. Therefore, monthly sediment samples from March to November 2002 were examined at two adjacent stations (reference station without mat, microbial mat station). Biomass (chlorophyll a content), cyanobacterial and diatom abundance, species composition and diversity were determined. The main mat forming cyanobacteria were Microcoleus chthonoplastes and Lyngbya aestuarii. The laminated mat exhibited a larger total biomass from spring on, while diatoms at the reference station accumulated relatively more biomass until late summer. 93 diatom taxa were identified in total. The species compositions at both stations were similar compared to those inhabiting other sandy and shallow water areas of the Baltic Sea. However, in the mat inhabiting diatom community lower relative abundances of very small species (<15 μm) were determined. In contrast to tidal flats, diatoms of the wind flat were found in much deeper zones of the mat (down to 1 cm), which may contribute to less anoxic conditions. This occurrence may be influenced by the specific sediment features, such as larger sand grain sizes. Species numbers were moderate within a given sample, indicating that environmental conditions in wind flats are extreme and outside of the tolerance limits of many species. On the other hand, the Shannon–Weaver index was comparably high due to its evenness component, so that disturbances may have been too frequent to establish climax communities, i.e. supporting few strongly dominant species. Nevertheless, the total biomass accumulated in the range of many other microphytobenthos communities in spite of extreme conditions hinting on good adaptation and protection capabilities, e.g. mucous material with high water retention potential.

Response of the estuarine cyanobacterium Lyngbya aestuarii to UV-B radiation

Growth response and changes in the spectral properties of methanolic extract of an estuarine cyanobacterium, Lyngbya aestuarii Agardh, to UV-B radiation were studied. Increase in growth accompanied by increase in chlorophyll a, protein and carbohydrate content was observed up to 12 h of UV-B irradiation followed by a decline with further increase in the duration of UV exposure. Carotenoid content progressively increased with the UV-B dose. The organism synthesized, to a significant extent, mycosporine amino acid-like substances (MAAs) upon UV-B exposure. The cells in the trichome became coiled followed by formation of small bundles as a response to UV-B radiation. SDS protein profile of the UV irradiated cells showed repression of 20 and 22 kDa proteins. However, irradiation with UV-B for 6–24 h led to overproduction of 84, 73, 60, 46, 40, 37 KDa proteins, possibly conferring protection to the organism from UV-B. UV irradiated cells cultured in florescent light for up to 7 days showed revival from UV damage of the pigments and macromolecular contents, suggesting existence of a repair mechanism in the organism.

Biolaminóides calcários holocênicos da lagoa Vermelha, Brasil

Lagoa Vermelha lies within the coordinates 22º55'39 - 22º56'06 S and 42º2129 - 42º24'13 W and is part of Araruama lagoon complex. Its dimensions are 4,400 m in length, 250 - 850 m in width, with approximate area of 2,400 m² and 0,2 - 1,7 m in depth. The study was based on six monthly collections in five stations over the north - east lagoon's margins from where was taken 20 samples of biolaminoids. To determinate the microbial composition of all different kinds of biolamonoids was made fresh and permanent slides and its analysis was carried out by microscopy. It was found three different kinds of microbial mats distributed throughout all five stations and were called: flat, polygonal and pustuled. Flat and polygonal microbial mats show itself layered, while pustuled show homogeneous structures. Layered and homogeneous ones present the same kind of main cyanobacterias, however layered mats in superficial stratum show preponderance of filamentous species and coccoid species in the bottom. Analysis showed a total of 33 species of cyanobacterias confirming it as main biolaminod component.The flat biolaminoid was mainly formed by Lyngbya aestuarii, the polygonal biolaminoid showed itself composed by Microcoleus chthonoplastes and the pustular biolaminoid was characterized by the presence of the cyanobacteria Chlorogoea tuberculosa. The cyanobacterial dominance is justified through its high morphologic adaptations that ensure its survival in many environments and prevail over in hipersaline local.

Isolation and characterization of cyanobacteria from microbial mats of the Ebro Delta, Spain.

Isolation and identification of several strains of cyanobacteria from microbial mats of the Ebro Delta, Spain, are described. A series of tenfold dilutions was the first step of isolation. Self-isolation techniques, which use one or several physiological characteristics of a cyanobacterium, were applied in some cases to obtain enrichment cultures. Twelve filamentous strains were isolated and stored in axenic culture. As only a few cyanobacterial species can be frozen and revived without any cryoprotective agent, preservation of isolated strains was assayed with several cryoprotective solutions. Methanol and glycerol were not suitable as cryoprotective agents for most of the isolates. Dimethyl sulfoxide (DMSO) was apparently the best cryoprotector. A new method, which used a filter paper as a growing substratum that later could be directly stored at -80 degrees C, was successfully used. A morphological study of each strain under light and electron microscopy was made to classify them. All isolated strains belong to phylum BX, Class 1, subsection III of the Bergey's manual of systematic bacteriology, 2nd ed., vol. 1. Most genera are included in the LPP group as Lyngbya aestuarii and Microcoleus chthonoplastes.

Microbial signatures in peritidal siliciclastic sediments: a catalogue

A catalogue of microbial structural signatures is presented, based upon the coupling of fundamental biogeochemical–microbial processes and local morphogenetic determinants. It summarizes a collection of sedimentary structures obtained from two modern siliciclastic peritidal environments in different climatic zones (temperate humid: Mellum Island, southern North Sea; subtropical arid: coast of southern Tunisia). Textural geometries reveal a high structural diversity, but their determinants are primarily based upon six major parameters: (1) intrinsic biofactors: structural diversification of sedimentary microbial films and mats inherent in the organisms, i.e. their construction morphology, growth, taxis and behaviour, and local abundance of specific morphotypes. Most prominent are the ensheathed filamentous cyanobacteria Microcoleus chthonoplastes and Lyngbya aestuarii, and the sheathless filamentous cyanobacterium Oscillatoria limosa. (2) Biological response to physical disturbances: sediment supply, erosion and fracturing of surface layers resulting from desiccation cause growth responses of biofilms and microbial mats. (3) Trapping/binding effects: physicobiological processes give rise to grain orientations and wavy to lenticular lamina, lamina‐specific grain arrangements and ‘sucrose’ calcium carbonate accumulations. (4) Secondary physical deformation of biogenic build‐ups: mechanical stresses acting upon sediments overgrown and biostabilized by biofilms and mats produce erosional and overthrust structures. (5) Post‐burial processes: textural fabrics that evolve from mechanical effects of gas formation from decaying mats, and features related to the formation of authigenic minerals (calcium carbonates, calcium sulphates, pyrite). (6) Bioturbation and grazing: post‐depositional structures, such as Skolithos‐type dwellings, traces of burrowing insects, gastropod grazing traces and faecal pellets. In synopsis, the catalogue firstly comprises a sound set of ubiquitous signatures. This uniformity in architectural characteristics is attributed to the presence and local dominance of certain microbes throughout the different settings. The catalogue secondly documents signatures that are extremely sensitive to tidal position, hydrodynamic regime and overall climatic conditions. These kinds of signature indicate narrow facies zones, which often coincide with the activity or dominance zones of certain organisms. An overview of structures of microbial origin from the fossil record underlines the potential of many of the signatures included in this catalogue to become fossilized and provide strong indicators of former siliciclastic tidal settings.

The Effects of UV Radiation A and B on Diurnal Variation in Photosynthesis in Three Taxonomically and Ecologically Diverse Microbial Mats

Abstract— Photosynthetic primary production, the basis of most global food chains, is inhibited by UV radiation. Evaluating UV inhibition is therefore important for assessing the role of natural levels of UV radiation in regulating ecosystem behavior as well as the potential impact of stratospheric ozone depletion on global ecosystems. As both photosynthesis and UV fluxes are subject to diurnal variations, we examined the diurnal variability of the effect of UV radiation on photosynthesis in three diverse algal mats. In one of the mats (Cyanidium caldarium) a small mean decrease in primary productivity over the whole day occurred when both UVA and UVB were screened out. In two of the mats (Lyngbya aestuarii and Zygogonium sp.) we found a mean increase in the total primary productivity over the day when UVB alone was screened and a further increase when UVA and UVB were both screened out. Variations in the effects of UV radiation were found at different times of the day. This diurnal variability may be because even under the same solar radiation flux, there are different factors that may control photosynthetic rate, including nutritional status and other physiological processes in the cell. The results show the importance of assessing the complete diurnal productivity. For some of the time points the increase in the mean was still within the standard deviations in primary productivity, illustrating the difficulty in dissecting UV effects from other natural variations.

Carbohydrate diagenesis in hypersaline environments: application of GC-IRMS to the stable isotope analysis of derivatized saccharides from surficial and buried sediments

The stable carbon isotope ratios of individual neutral monosaccharides isolated from microbial mats, mangrove tissue and paleosoils from the Abu Dhabi lagoon-sabkha system were determined by gas chromatography-isotope ratio mass spectrometry (GC-IRMS). Neutral monosaccharides in hydrolysates from surficial and buried “flat” mats dominated by the filamentous cyanobacteria Microcoleus chtonoplastes and Lyngbya aestuarii, have δ 13C (PDB) averaging −5.6 ± 1.3 and −4.6 ± 1.5% respectively. This is the first time such heavy δ 13c values have been reported for individual biosynthetic components, to our knowledge. So-called “blister” mats, formed by decomposition of flat mats by aerobic bacteria, yield slightly lower δ 13C values for individual monosaccharides around −10.4 ± 1.4%. The stable carbon isotope ratios of the monosaccharides isolated from the fresh mangrove leaf ( Avicennia marina) are low with δ 13C around −22.5 ± 2.6%, typical for low latitude C3 plants. Neutral monosaccharides from the mangrove paleosoils from 1250 and 6000 yr BP, however, have δ 13C of −16.0 ± 1.2 and −13.8 ± 2.9% respectively. This is attributed to the presence of anaerobic bacterial contributions in the palesoils. The δ 13C values of saccharides from the paleosoils indicate that galactose, mannose and fucose are mainly derived from bacteria, whereas glucose and arabinose still seem to be largely derived from the mangrove tissues.

Neutral monosaccharides from a hypersaline tropical environment: Applications to the characterization of modern and ancient ecosystems

Surficial and buried sediment samples from a hypersaline lagoon-sabkha system (Abu Dhabi, United Arab Emirates) were analysed for carbohydrates (as neutral monosaccharides) to distinguish and characterise various types of recent and ancient tropical ecosystems on a molecular level. The samples consisted of surficial and buried microbial mats, lagoonal sediments containing seagrass ( Halodule uninervis), and mangrove ( Avicennia marina) paleosoils and handpicked mangrove leaves, ranging in age from contemporary to ca. 6000 yr Bp. Analysis of quantitative neutral monosaccharide data by multivariate techniques shows that various groups can be distinguished: intact vascular plant material (mangrove leaf) contains high amounts of arabinose and glucose and hardly any partially methylated monosaccharides, whereas microbial mats in general and lagoonal seagrass sediments show high contributions of fucose, ribose, mannose, galactose and partially methylated monosaccharides. Moreover, surficial microbial mats consisting of filamentous cyanobacteria ( Microcoleus chtonoplastes, Lyngbya aestuarii) can be distinguished from other mats and sediments containing coccoid cyanobacteria ( Entophysalis major) and/or fermenting, sulphate reducing, and methanogenic bacteria on the basis of high contributions of specific groups of partially methylated monosaccharides and other “minor” saccharides. The neutral monosaccharides present in mangrove paleosoils are for a substantial part derived from microorganisms.

Nucleation of calcite on the sheaths of cyanobacteria using a simple diffusion cell

Abstract A method allowing observation of calcium carbonate nucleation on the sheaths of cyanobacteria and other microorganisms is described. Nucleation of calcite was obtained on the sheaths of Lyngbya aestuarii and Scy‐tonema myochrous cultures but not on Entophysalis major and Pseudanabaena minuta. Differences in the rate of nucleation were also noted in media of differing salinity.

SYSTEMATICS AND ECOLOGY OF LYNGBYA SPP. AND ASSOCIATED SPECIES (CYANOPHYTA) IN A NEW ENGLAND SALT MARSH1,2

ABSTRACTField populations of the most abundant filamentous blue‐green algae (cyanobacteria) from a northern New England salt marsh were examined for the presence of natural morphological clusters. A continuum in the distribution of average cell sizes and shapes for individual trichomes was evident. However, there was a high frequency of certain cell sizes (six cluster, which were also separated by several qualitatives characters (end cell shape, granule location, and cell color). In clonal cultures the trichomes of these culsters maintained the morphology of the original isolated trichome and thus morphology apperated to be stable. The clusters were either named according to Gietler's (1932.) terminology or assigned numbers if no adequate descriptions were availble: (1) Lyngyya and Phormidium spp., (2) Microcoleus chthonoplastes Thur. (3) Lyngbya sp.1, (4)Lyngbya sp. 2 (5) Lyngbya aestruarii (Mert.) Liebmann, and, (6) Lyngbya aestuarii (mert. Liebmann, and, (6) Lyngbya sp. 3. All goups had maximum asbundance in late summer. Microcoleus chthonoplastes occurred throughtout the; year, while Lyngbya aestuarri and Lynobya sp. 3 occurred throughout the summer and fall. It is concluded that both field and culture information are useful in enhancing our knowledge of blue‐green algal systematics.

SYSTEMATICS AND ECOLOGY OF LYNGBYA SPP. AND ASSOCIATED SPECIES (CYANOPHYTA) IN A NEW ENGLAND SALT MARSH1,2

ABSTRACTField populations of the most abundant filamentous blue‐green algae (cyanobacteria) from a northern New England salt marsh were examined for the presence of natural morphological clusters. A continuum in the distribution of average cell sizes and shapes for individual trichomes was evident. However, there was a high frequency of certain cell sizes (six clusters), which were also separated by several qualitative characters (end cell shape, granule location, and cell color). In clonal cultures the trichomes of these clusters maintained the morphology of the original isolated trichome and thus morphology appeared to he stable. The clusters were either named according to Geitler's (1932) terminology or assigned numbers if no adequate descriptions were available: (1) Lyngbya and Phormidium spp., (2) Microcoleus chthonoplastes Thur. (3) Lyngbya sp. 1, (4) Lyngbya sp. 2, (5) Lyngbya aestuarii (Mert.) Liebmann. and, (6) Lyngbya sp. 3. All groups had maximum abundance in late summer. Microcoleus chthonoplastes occurred throughout the year, while Lyngbya aestuarii and Lyngbya sp. 3 occurred throughout the summer and fall. It is concluded that both field and culture information are useful in enhancing our knowledge of blue‐green algal systematics.

Diel N 2 fixation in an intertidal marine cyanobacterial mat community

Diurnal and diel rates of nitrogen fixation (acetylene reduction) were measured in an intertidal marine mat community consisting of Microcoleus chthonoplastes, Lyngbya aestuarii, and an underlying layer of anaerobic bacteria (probably photosynthetic, fermentative, and sulfate reducing bacteria). The community is located on Shackleford Banks, a barrier island off the coast of North Carolina. Rates of nitrogenase activity during the diurnal period were generally highest in the morning. Rates measured during the day, but incubated in the dark, at times equalled those of samples incubated continuously in the light. Fixation also occurred at night. Mat samples deprived of light prior to the acetylene reduction assay continued to reduce acetylene during the night and into the following day, although at lower rates than samples exposed to light. The persistence of dark nitrogenase activity serves as evidence that reducing power initially generated through photosynthesis can be stored and subsequently utilized through heterotrophic metabolism. Although cyanobacteria are responsible for light-mediated nitrogenase activity, non-photosynthetic bacterial contributions to dark-mediated nitrogenase activity cannot be ruled out.

Peuplements benthiques à Cyanophycées des marais salants de Salin-de-Giraud (Sud de la France)

In Salin-de-Giraud solar salt work pools, Cyanophyceae are dominant in benthic populations. Two main types of communities can be recognized : 1) Laminated mats in weak salinity areas (&lt;150 g/1) with Microcoleus chthonoplastes frequently exclusive (but which may be covered by a Lyngbya aestuarii layer), being the result of superposition in time of two competitive phenomena : Cyanophycean growth and sedimentary contribution either of detrital or chemical origin. As the gypsum precipitation occurs, Microcoleus mats disappear. 2) Communities associated with gypsum and halite crusts. In gypsum pools, they may be composed of several layers : a) a lower purple layer of ph.otosynthetic bacteria ; b) a mid dark-green layer of filamentous Cyanophyceae (Phormidium and Spirulina species) mixed with some coccoids (Aphanothece div. sp. essentially) ; c) an upper orange-colored layer of coccoids (with an Aphanothece sp. as major component) may grow during summer, but disappears during winter when pools are emptied, which is the rule in Salin-de-Giraud. The basal level of halite crust is colonized by a filamentous form Phormidium sp. For these communities, stratification of species is associated to physiological properties of organisms, and sedimentary deposits only act as a support in such pools.

Laminated microbial mats, laguna Guerrero Negro, Mexico

Laguna Guerrero Negro and Ojo de Liebre are large, restricted embayments characterized by an arid climate and by a salinity ranging from that of normal seawater to the hypersalinity of sabkha environments. Intertidal microbial mats develop in some of the slightly hypersaline marshes and in many of the moderately hypersaline flats. Each major mat type corresponds to the lower, middle, or upper intertidal. In the lower intertidal mat, the photosynthetic horizon is a bilayer composed of: 1) a surface, blue‐green algal layer (about 3‐mm thick) dominated by Microcoleus chthonoplastes; and 2) an underlying purple layer (about 2‐mm thick) of photosynthetic bacteria, predominantly Chromatium sp. The mat may accrete to a thickness of 10 cm or more. It is characterized by fine laminations of alternating layers of blue‐green algae and of photosynthetic bacteria. The middle intertidal mat, dominated by Lyngbya aestuarii, is relatively thin (usually 1 or 2 cm). Only a very thin, lower horizon of purple photosynthetic ...

Blue-green algae (Cyanophyta) in marine coastal environments of the Sinai Peninsula; distribution, zonation, stratification and taxonomic diversity

Abstract Eighty-four species of blue-green algae were recorded from the intertidal zone of the Gulf of Elat (Aqaba) and four hypersaline coastal pools. Heterocystous forms (sixteen) were restricted to the intertidal, although significant rates of nitrogen fixation (acetylene reduction) were measured in non-heterocystous communities in coastal pools. Species distribution, the colour and surface morphology of thick mats are determined by salinity, frequency of wetting and desiccation. Distinct horizontal zonation patterns occur in coastal pools. Coccoid and non-filamentous forms such as Entophysalis and Pleurocapsa grow associated with gypsum crusts around the periphery of the pools, while filamentous forms (Lyngbya, Microcoleus) become abundant towards the central regions. Complex stratification is apparent in many communities. In different coastal pools mat communities have a similar structure; Lyngbya aestuarii and pennate diatoms at the surface, then coccoid blue-green algae (Aphanorhece, Synechococcus)...

Nitrogen fixation (acetylene reduction) associated with communities of heterocystous and non-heterocystous blue-green algae in mangrove forests of Sinai.

High rates of nitrogen fixation (acetylene reduction) are associated with communities of heterocystous and non-heterocystous blue-green algae, which are widespread and abundant in the coastal mangrove forests of the Sinai Peninsula.Heterocystous forms, particularly representatives of the Rivulariaceae, grow in aerobic environments, where nitrogenase activity may be limited by the availability of nutrients such as Fe and PO4-P. Desiccated communities of Scytonema sp. reduce acetylene within ten minutes of wetting by tidal sea water. Communities dominated by the non-heterocystous Hydrocoleus sp., Hyella balani, Lyngbya aestuarii, Phormidium sp. and Schizothrix sp., occur in close contact with anaerobic sediments and reduce acetylene in the dark as well as in the light.Nitrogen fixation in all these communities is light dependant and may be supplemented by an alternative source of reductant in the dark. The indications are that nitrogen fixation by these communities of blue-green algae, makes a significant contribution to the overall nitrogen input of the mangrove ecosystem.

A biogeochemical study of the Abu Dhabi algal mats: A simplified ecosystem

A variety of lipid classes (alkanes, alkenes, carboxylic acids, carotenoids, saturated alcohols, sterols and stanols) in a core from an intertidal, tropical algal mat (Abu Dhabi, Persian Gulf) have been analysed. The n-alkanes and n-alkanoic acids maximise at n-C17 and n-C16, respectively, and show little or no contribution from homologues > C20. No evidence of pollution from petroleum products is apparent in the branched/cyclic alkanes, which have a simple distribution and contain the unresolved mixture of 7- and 8-methylheptadecanes as a relatively abundant component. Among the major carotenoids, components assigned as β-carotene, torulene, echinenone, spirilloxanthin, rhodopin, 3,4-dehydrorhodopin, zeaxanthin and myxoxanthophyll were present. The distributions of these classes show little or no evidence of a higher-plant contribution and are compatible with the most abundant micro-organisms identified in the core, viz., Lyngbya aestuarii and Microcoleus chthonoplastes (blue-greens), and Chromatium and Thiocystis spp. (purple photosynthetic bacteria). The presence of torulene suggests fungal activity.Only Δ5 or Δ5,22 sterols were observed and their distributions cannot be related at present to specific inputs. However, the distributions of all of the compound classes show features which have been observed in similar analyses of other blue-green algal mat situations.

Lyngbya Mats at Laguna Mormona, Baja California, Mexico: Comparison with Proterozoic Stromatolites

ABSTRACT Lyngbya aestuarii, an oscillatoriacean cyanophyte, forms surficial mats in portions of the salt marsh and evaporite flat at Laguna Mormona, a closed coastal lagoon on the Pacific coast of Baja California. Aggregations of this alga produce structures ranging from small-diameter mounds to tufts, rounded ridges, sharp-crested ridges, large-diameter flat-topped mounds, and rings. The specific structural type seems to be controlled largely by the overall filament abundance, flooding history, and water depth. Study of these Lyngbya aestuarii mats and associated tufted structures produced by other oscillatoriacean cyanophytes have a bearing on certain problems in Precambrian paleontology, including: the formation of the stromatolite Conophyton; the origin of molar-tooth structure; and the effect of environmental factors on algal-mat structure.

Laminated Algal Mats from a Coastal Lagoon, Laguna Mormona, Baja California, Mexico

ABSTRACT Laminated algal mats are well developed at Laguna Mormona, a closed hypersaline lagoonal complex on the west coast of Baja California, Mexico. These mats and underlying organic accumulations attain a maximum thickness of 30 cm. Their morphology is controlled mainly by the degree of desiccation: mound-shaped structures develop under conditions of permanent submergence; flat-topped mounds and horizontal mats broken by desiccation cracks occur in settings where the mats have grown up to the water surface; and mats curved into concave-upward saucers develop under conditions of extreme desiccation. The accumulation rate in these mats is several millimeters per year, with one to several laminae forming per year. Filamentous cyanophytes (viz., Microcoleus chthonoplastes and several species of Lyngbya), a coccoid cyanophyte (Entophysalis sp.), and diatoms contribute to the primary organic deposit which is subsequently degraded and modified by bacterial activity. Sheaths, rather than trichomes, of the oscillatoriacean cyanophytes occur at depth in these mats: this is due largely to the motile nature of the trichomes which glide upward leaving empty sheaths behind. However, it also appears that the sheaths of M. chthonoplastes and Lyngbya aestuarii are more resistant to degradation than are the trichomes, and sheaths of the colonial coccoid Entophysalis are more resistant to degradation than are their cellular contents. Although these modern mats are not being permineralized by silica, many aspects of their macro-structure, lamina structure, and biology are applicable to the interpretation of silicified Proterozoic mats and their contained microbiotas.

Hydrocarbons of geochemical significance in microscopic algae

Recent investigations have implicated a correlation between the hydrocarbon composition of algae and that found in geological sediments. This report presents information on hydrocarbon production by twelve species of algae, morphologically similar to fossil forms, including Anacystis cyanea, A. montana, Spirulina platensis, Lyngbya aestuarii, Chroococcus turgidus, Chlorella pyrenoidosa, Coelastrum microsporum, Tetraedron sp. and Scenedesmus quadricauda, along with confirmatory data on Anacystis nidulans, Nostoc sp. and Botryococcus braunii which have previously been reported. The normal hydrocarbon range is from C15 to C19 in most species, and n-C17 is predominant in all cultures. However, a few of the species show a bimodal distribution of aliphatic hydrocarbons with maxima at C17 and C27, with significant amounts of C23, C27, and C29 straight-chain olefins and paraffins. Similar bimodal distributions of saturated hydrocarbons have been observed in both tertiary and Precambrian sediments, supporting the interpretation of biological origin. The production of methyl-substituted alkanes by blue-green algae and a tentative identification of a triterpene from three species is also reported. Squalene is the only isoprenoid reported.