Pristane in the marine environment

Summary 1. Methods are described for the sensitive determination of pristane and similar hydrocarbons in individual planktonic organisms and for the isolation of pristane from copepod oil.2. Pristane (2, 6, 10, 14-tetramethylpentadecane) occurs in unusually high concentrations (1–3% of the body lipid) inCalanus finmarchicus, C. glacialis, andC. hyperboreus, and at lower concentrations in a wide range of planktonic animals from the Gulf of Maine and continental slope waters.3. A predator,Paraeuchaeta norvegica, contains pristane at an intermediate level between that ofCalanus and the other herbivores, probably as a result of feeding onCalanus.4. On the basis of relative abundance and structural similarity, phytol is suggested as the precursor of pristane in herbivorous zooplankton.5. Pristane content is unaltered or increased during the metabolism of the major deposit lipids ofCalanus hyperboreus during starvation in the laboratory or in nature. Because of its low density, pristane may contribute to the bouyancy ofCalanus, especially when the other lipids are metabolized.6. Pristane may prove useful as a biochemical integrator for the total assimilation of phytoplankton byCalanus.7. Some planktonic organisms may be characterized by the presence of specific compounds, e. g. pristane inCalanus and several unknown compounds inRhincalanus.8. Specific products of organisms of limited geographical occurence may prove useful as biochemical tags of water masses.

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Pristan in der marinen Umwelt

Kurzfassung Pristan (2, 6, 10, 14-Tetramethylpentadecan) kommt in niedriger Konzentration in manchen planktonischen Tieren des Golfs von Maine, USA, und der Gewässer des kontinentalen Schelfes vor. Dieser Kohlenwasserstoff leitet sich vermutlich vom Phytol in der Nahrung der planktonischen Herbivoren ab. Seine Konzentration ist ungewöhnlich hoch inCalanus finmarchius, C. glacialis undC. hyperboreus, wo er möglicherweise als auftriebsregulierende Substanz in Hungerzeiten wichtig ist. Arten, wieParaeuchaeta norvegica, welcheCalanus verzehren, stellen sekundäre Pristanquellen innerhalb der marinen Nahrungskette dar. Die proCalanus-Individuum angetroffene Pristanmenge könnte als Indikator für die gesamte Nahrungsassimilation dienen. Pristan und andere artspezifische Stoffe können in das die Individuen umgebende Wasser gelangen und dann als biochemische Markierungs-Substanzen dienen.

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Contribution No. 1438 of the Woods Hole Oceanographic Institution.     

Limulus vision in the marine environment

Horseshoe crabs use vision to find mates. They can reliably detect objects resembling potential mates under a variety of lighting conditions. To understand how they achieve this remarkable performance, we constructed a cell based realistic model of the lateral eye to compute the ensembles of optic nerve activity ("neural images") it transmits to the brain. The neural images reveal a robust encocding of mate-like objects that move underwater during the day. The neural images are much less clear at night, even though the eyes undergo large circadian increases of sensitivity that nearly compensate for the millionfold decreasein underwater lighting after sundown. At night the neurral images are noisy, dominated by bursts of nerve impulses from random photon events that occur at low nighttime levels of illumination. Deciphering the eye's input to the brain begins at the first synaptic level with lowpass temporal and spatial filtering. Both neural filtering mechanisms improve the signal-to-noise properties of the eye's input, yielding clearer neural images of potential mates, especiallyat night. Insights about visual processing by the relatively simple visual system of Limulus may aid in the designof robotic sensors for the marine environment.     

Gene transfer in the marine environment

Abstract This review summarises the literature on bacterial gene transfer in marine ecosystems. Relevant experiments carried out in model systems are also included. Prerequisites for the main gene transfer mechanisms, transformation, transduction and conjugation are discussed, such as concentrations of extracellular DNA in marine waters, numbers of bacteriophages in sea water and frequency of plasmids in marine bacteria. Transfer of chromosomal genes as well as plasmids are considered. We also discuss the possibility that gene transfer is more frequent in surface-associated bacterial communities. Examples of relevant studies using various solid surfaces and from the air-water interface are summarized. We suggest that there is a higher ‘flow-rate’ of genetic information through surface-associated communities compared to bulk water communities.     

Chemical signaling processes in the marine environment

Understanding the mechanisms by which environmental chemical signals, chemical defenses, and other chemical agents mediate various life-history processes can lead to important insights about the forces driving the ecology and evolution of marine systems. For chemical signals released into the environment, establishing the principles that mediate chemical production and transport is critical for interpreting biological responses to these stimuli within appropriate natural, historical contexts. Recent technological advancements provide outstanding opportunities for new discoveries, thus allowing quantification of interactions between hydrodynamic, chemical, and biological factors at numerous spatial and temporal scales. Past work on chemically mediated processes involving organisms and their environment have emphasized habitat colonization by larvae and trophic relationships. Future research priorities should include these topics as well as courtship and mating, fertilization, competition, symbiosis, and microbial chemical ecology. There are now vast new opportunities for determining how organisms respond to chemical signals and employ chemical defenses under environmentally realistic conditions. Integrating these findings within a larger ecological and evolutionary framework should lead to improved understanding of natural physicochemical phenomena that constrain biological responses at the individual, population, and community levels of organization.     

Plant defense associations in the marine environment

In contrast to terrestrial systems, few positive plant-plant associations have been recorded in tropical reef environments. This study, conducted at Carrie Bow Cay, Belize during 28 March–10 April 1984, provides the first documentation of herbivore escapes for natural combinations of palatable and unpalatable marine plants. For example, there was a highly significant association of several macrophyte taxa (Laurencia poitei, Dictyota spp., Amphiroa fragilissima, Cladophoropsis macromeres, Galaxaura cylindrica, rhodophycean turf) within a 2.0-cm radius of the herbivore-resistant brown alga Stypopodium zonale. Almost twice as many taxa occurred within 10 cm of S. zonale as within 10 cm of an equal number of random Stypopodium-free points, and there were no algal species negatively associated with S. zonale. The association of A. tribulus, L. poitei, Digenia simplex, rhodophycean turf, and Jania adherens with S. zonale provided them a fourfold greater survivorship per 48 h in the presence of grazing activity by fishes (mainly Acanthuridae and Scaridae). Reduced herbivory by fishes on macroalgae associated with S. zonale was not solely a consequence of its structural aspect. Losses of the palatable alga Acanthophora spicifera were significantly greater for thalli spatially remote (30 and 60 cm) from either a real or simulated Stypopodium; however, losses of A. spicifera adjacent to actual Stypopodium plants were significantly less than the losses next to models. The inter-relationships studied here, where an abundant and well-defended plant provides a significant refuge habitat for at least five relatively edible macroalgae, clearly facilitates the survival of certain taxa in the reef system and concomitantly enhances the within habitat diversity. Our findings also suggest an interaction counter to the process of competitive exclusion, since the single predominant plant has a positive rather than negative net effect on the abundances of other species that utilize the same general resources (e.g., light, space, nutrients).     

Planktic cyanophytes in marine environment

Abstract

Few major groups of cyanophytes contribute significantly to the productivity of oceanic oligotrophic ecosystem: unicellular Synechococcus spp., and filamentous nitrogen-fixing Trichodesmium and Richelia species occur as abundant populations in open seas and oceans. In addition, oceanic eutrophic waters support the development of massive summer-blooms of Nodularia, Aphanizomenon and Anabaena in the Baltic Sea. The importance of the planktic cyanophytes as primary producers and their contribution to the input of new fixed nitrogen in the euphotic zone is underlined.     

Dynamics of extracellular DNA in the marine environment

The production and turnover of dissolved DNA in subtropical estuarine and oligotrophic oceanic environments were investigated. Actively growing heterotrophic bacterioplankton (i.e., those capable of [3H]thymidine incorporation) were found to produce dissolved DNA, presumably through the processes of death and lysis, grazing by bacteriovores, and excretion. Production of dissolved DNA as determined by [3H]thymidine incorporation was less than or equal to 4% of the ambient dissolved DNA concentration per day. In turnover studies, the addition of [3H]DNA (Escherichia coli chromosomal) to seawater resulted in rapid hydrolysis and uptake or radioactivity by microbial populations. DNA was hydrolyzed by both cell-associated and extracellular nucleases, in both estuarine and offshore environments. Kinetic analysis performed for a eutrophic estuary indicated a turnover time for dissolved DNA as short as 6.5 h. Microautoradiographic studies of bacterial populations in Tampa Bay indicated that filamentous and attached bacteria took up most of the radioactivity from [3H]DNA. Dissolved DNA is therefore a dynamic component of the dissolved organic matter in the marine environment, and bacterioplankton play a key role in the cycling of this material.     

Longevity of marine cystophorous cercariae in the environment

Experiments were conducted on the duration of life in sea water of three species of cystophorous cercariae from the Barents sea. The expenditure of reserve nutritive substances (glycogene) in the process of the vital activity of cercariae was followed. The life duration of cystophorous cercariae is considerably longer than that cited in literature for other groups of cercariae that is associated with their morphological and biological peculiarities.     

Dynamics of extracellular DNA in the marine environment.

The production and turnover of dissolved DNA in subtropical estuarine and oligotrophic oceanic environments were investigated. Actively growing heterotrophic bacterioplankton (i.e., those capable of [3H]thymidine incorporation) were found to produce dissolved DNA, presumably through the processes of death and lysis, grazing by bacteriovores, and excretion. Production of dissolved DNA as determined by [3H]thymidine incorporation was less than or equal to 4% of the ambient dissolved DNA concentration per day. In turnover studies, the addition of [3H]DNA (Escherichia coli chromosomal) to seawater resulted in rapid hydrolysis and uptake or radioactivity by microbial populations. DNA was hydrolyzed by both cell-associated and extracellular nucleases, in both estuarine and offshore environments. Kinetic analysis performed for a eutrophic estuary indicated a turnover time for dissolved DNA as short as 6.5 h. Microautoradiographic studies of bacterial populations in Tampa Bay indicated that filamentous and attached bacteria took up most of the radioactivity from [3H]DNA. Dissolved DNA is therefore a dynamic component of the dissolved organic matter in the marine environment, and bacterioplankton play a key role in the cycling of this material.     

An assessment of actinobacterial diversity in the marine environment

The 16S rRNA gene sequence diversity within the Phylum Actinobacteria was assessed from four sources: PCR-generated V6 sequence tags derived from seawater samples, metagenomic data from the Global Ocean Sampling (GOS) expedition, marine-derived sequences maintained in the Ribosomal Database Project (RDP), and select cultured strains for which sequence data is not yet available in the RDP. This meta-analysis revealed remarkable levels of phylogenetic diversity and confirms the existence of major, deeply rooted, and as of yet uncharacterized lineages within the phylum. A dramatic incongruence among cultured strains and those detected using culture-independent techniques was also revealed. Redundancy among the actinobacteria detected using culture-independent techniques suggests that greater sequence coverage or improved DNA extraction efficiencies may be required to detect the rare phylotypes that can be readily cultured from marine samples. Conversely, new strategies need to be developed for the cultivation of frequently observed but yet to be cultured marine actinobacteria.     

Salmon aquaculture and antimicrobial resistance in the marine environment

Antimicrobials used in salmon aquaculture pass into the marine environment. This could have negative impacts on marine environmental biodiversity, and on terrestrial animal and human health as a result of selection for bacteria containing antimicrobial resistance genes. We therefore measured the numbers of culturable bacteria and antimicrobial-resistant bacteria in marine sediments in the Calbuco Archipelago, Chile, over 12-month period at a salmon aquaculture site approximately 20 m from a salmon farm and at a control site 8 km distant without observable aquaculture activities. Three antimicrobials extensively used in Chilean salmon aquaculture (oxytetracycline, oxolinic acid, and florfenicol) were studied. Although none of these antimicrobials was detected in sediments from either site, traces of flumequine, a fluoroquinolone antimicrobial also widely used in Chile, were present in sediments from both sites during this period. There were significant increases in bacterial numbers and antimicrobial-resistant fractions to oxytetracycline, oxolinic acid, and florfenicol in sediments from the aquaculture site compared to those from the control site. Interestingly, there were similar numbers of presumably plasmid-mediated resistance genes for oxytetracycline, oxolinic acid and florfenicol in unselected marine bacteria isolated from both aquaculture and control sites. These preliminary findings in one location may suggest that the current use of large amounts of antimicrobials in Chilean aquaculture has the potential to select for antimicrobial-resistant bacteria in marine sediments.     

Detection of photoactive siderophore biosynthetic genes in the marine environment

Iron is an essential element for oceanic microbial life but its low bioavailability limits microorganisms in large areas of the oceans. To acquire this metal many marine bacteria produce organic chelates that bind and transport iron (siderophores). While it has been hypothesized that the global production of siderophores by heterotrophic bacteria and some cyanobacteria constitutes the bulk of organic ligands binding iron in the ocean because stability constants of siderophores and these organic ligands are similar, and because ligand concentrations rise sharply in response to iron fertilization events, direct evidence for this proposal is lacking. This lack is due to the difficulty in characterizing these ligands due both to their extremely low concentrations and their highly heterogeneous nature. The situation for characterizing photoactive siderophores in situ is more problematic because of their expected short lifetimes in the photic zone. An alternative approach is to make use of high sensitivity molecular technology (qPCR) to search for siderophore biosynthesis genes related to the production of photoactive siderophores. In this way one can access their “biochemical potential” and utilize this information as a proxy for the presence of these siderophores in the marine environment. Here we show, using qPCR primers designed to detect biosynthetic genes for the siderophores vibrioferrin, petrobactin and aerobactin that such genes are widespread and based on their abundance, the “biochemical potential” for photoactive siderophore production is significant. Concurrently we also briefly examine the microbial biodiversity responsible for such production as a function of depth and location across a North Atlantic transect.     

Complications in the determination of the nutrient status of the marine environment

How much of the organic matter in the oceans is truly bioavailable under in situ conditions? This bioavailability may be altered by perturbation, priming, bottle (surface or confinement) effects, and air contaminants. Measured free organic matter may not be free in situ but may depend on method of analysis. We have yet to determine the threshold energy for growth of microbes and their energy of maintenance under in situ conditions.