Carbon, nitrogen and phosphorus elemental stoichiometry in aquacultured and wild-caught fish and consequences for pelagic nutrient dynamics

The elemental carbon (C), nitrogen (N) and phosphorus (P) compositions of the whole-body and gut content of wild marine fish inhabiting the Bay of Biscay (Northeast Atlantic) were studied. Furthermore, the literature was examined for studies of aquacultured fish, reporting the elemental composition of the whole-body fish, that of their food, and nutrient assimilation and gross growth efficiencies (GGE). In both wild-caught and aquacultured fish, significant differences in C, N and P elemental composition were found between species, with P being the most variable component. Differences among species in terms of C, N and P content could be explained by varying proportions of storage compounds in whole-body fish, and varying degrees of ossification. Aquacultured fish feces were found to be P-rich, because of a lower P assimilation efficiency, compared to C or N assimilation efficiencies. Examination of aquacultured fish literature also revealed that C, N and P GGE and nutrient resupply ratios agreed with basic principles of homeostatic regulation of whole-body fish elemental composition. Extrapolation of the results to broader marine systems indicated that fish may be important for conveying nutrients toward the ocean interior.     

Bearded vultures (<Emphasis Type="Italic">Gypaetus barbatus</Emphasis>) prefer fatty bones

In animal species, prey processing and the provisioning of nutrients are subject to several constraints related with finding, ingesting and processing food. In most bird species, these constraints are obvious as a consequence of food morphology. In the case of the bearded vulture (Gypaetus barbatus), in comparison with other species, its behavioural and physiological adaptations apparently allow this vulture to ingest bone remains irrespective of their morphology. Here, by comparing bones delivered to the nest to be consumed (selected) and remains found at an experimental feeding station and at bone-breaking sites or ossuaries (rejected), I tested whether bearded vultures are capable of choosing from among the various anatomical parts of an animal carcass in relation to their fatty acid content (nutrient concentration hypothesis), their size (width-reduction hypothesis) or both. The results suggest that bearded vultures prefer the fatty anatomical parts (with a high percentage of oleic acid) of an animal carcass regardless of bone length, although bone morphology as a consequence of handling efficiency or the ingestion process may also play a secondary role in food selection. The close association between the bones selected and their high fat value implies an optimisation of foraging time and of the increased energy gained from the food. This is in line with selective foraging to redress specific nutritional imbalances (nutrient concentration hypothesis) and, secondarily, the width-reduction hypothesis.     

Do plant density, nutrient availability, and herbivore grazing interact to affect phlorotannin plasticity in the brown seaweed Ascophyllum nodosum

Plants have different strategies to cope with herbivory, including induction of chemical defences and compensatory growth. The most favourable strategy for an individual plant may depend on the density at which the plants are growing and on the availability of nutrients, but this has not been tested previously for marine plant–herbivore interactions. We investigated the separate and interactive effects of plant density, nutrient availability, and herbivore grazing on the phlorotannin (polyphenolic) production in the brown seaweed Ascophyllum nodosum. Seaweed plants grown at low or high densities were exposed either to nutrient enrichment, herbivorous littorinid gastropods (Littorina obtusata), or a combination of nutrients and herbivores in an outdoor mesocosm experiment for 2 weeks. Seaweeds grown at a low density tended to have higher tissue nitrogen content compared to plants grown at a high density when exposed to elevated nutrient levels, indicating that there was a density dependent competition for nitrogen. Herbivore grazing induced a higher phlorotannin content in plants grown under ambient, but not enriched, nutrient levels, indicting either that phlorotannin plasticity is more costly when nutrients are abundant or that plants responded to herbivory by compensatory growth. However, there were no significant interactive or main effects of plant density on the seaweed phlorotannin content. The results indicate that plants in both high and low densities induce chemical defence, and that eutrophication may have indirect effects on marine plant–herbivore interactions through alterations of plant chemical defence allocation.     

Predicting leadership using nutrient requirements and dominance rank of group members

Group members must decide collectively when and where to go despite their different nutrient requirements. One mechanism underlying consensus decisions is the proposition by one individual to move. The individual frequently initiating movements is often named a “leader”, and this individual may be the most dominant, the oldest or may have the greatest physiological needs. However, high-ranking individuals are often those with the highest body mass, and thus the highest nutrient requirements. In this study, we use a state-dependent model to assess the importance of dominance and nutrient requirements to the initiation of group movements, testing different combinations of effects of these interacting factors. We first show using a theoretical approach that whatever the correlation between the dominance hierarchy and body mass, all decision-making systems are viable (or stable). However, in most cases, one individual does become the leader, and nutrient requirements appear to be more important for determining which individual will emerge as the leader than pre-existing individual characteristics such as their dominance rank. We obtained the same result when we compared the simulated distributions of initiations to the observed distributions in three macaque species. Results of our comparison of three macaque groups suggest that we can predict which group member will be the leader simply by knowing its body mass and its reproductive state. Understanding the link between dominance, needs and leadership may be a key to understanding consensus decisions and collective motion in animal groups, and might provide insight into the management of animal groups and their conservation.     

Not just the usual suspects: insect herbivore populations and communities are associated with multiple plant nutrients

The relationship between plant nutrient content and insect herbivore populations and community structure has long interested ecologists. Insect herbivores require multiple nutrients, but ecologists have focused mostly on nitrogen (an estimate of plant protein content), and more recently phosphorus (P); other nutrients have received little attention. Here we document nutrient variation in grass and forb samples from grassland habitats in central Nebraska using an elemental approach; in total we measured foliar concentrations of 12 elements (N and P, plus S, B, Ca, Mg, Na, K, Zn, Fe, Mn, and Cu). We detected significant variability among sites for N, P, Mg, Na, K, and Cu. We next used a model selection approach to explore how this nutritional variation and plant biomass correlate with grasshopper densities (collectively and at the feeding-guild level), and principal component analysis to explore nutrient correlations with grasshopper community species composition. When all grasshoppers were pooled, densities varied among sites, but only P was associated with abundance of the elements shown to vary between sites. Different responses occurred at the feeding-guild level. For grass specialists, densities were associated with N, plus P, Mg, and Na. For forb specialists, N and P were often associated with density, but associations with Na and K were also observed. Finally, mixed-feeder abundance was strongly associated with biomass, and to a lesser extent P, Mg, Na, and Cu. At the community level, B, Ca, Zn, and Cu, plus biomass, explained > 30% of species composition variation. Our results confirm the positive association of N and P with insect herbivore populations, while suggesting a potential role for Mg, Na, and K. They also demonstrate the importance of exploring effects at the feeding-guild level. We hope our data motivate ecologists to think beyond N and P when considering plant nutrient effects on insect herbivores, and make a call for studies to examine functional responses of insect herbivores to dietary manipulation of Mg, Na, and K. Finally, our results demonstrate correlations between variation in nutrients and species assemblages, but factors not linked to plant nutrient quality or biomass likely explain most of the observed variation.     

Dietary-induced responses in the phagotrophic flagellate Oxyrrhis marina

Primary producers may be limited by different nutrients as well as by light availability, which in turn affects their quality as food for higher trophic levels. Typically, algae with high C:N and/or C:P ratios are low-quality food for consumers. Heterotrophic protists are important grazers on these autotrophes, but despite their importance as grazers, knowledge of food quality effects on heterotrophic protists is sparse. In the present study, we examined how differently grown Rhodomonas salina (nutrient replete, N-limited and P-limited) affected the phagotrophic flagellate Oxyrrhis marina. The functional response of O. marina (based on ingested biovolume) did not show significant differences between food sources, thus food uptake was independent of food quality. O. marina was weakly homoeostatic which means that its C:N:P ratio still reflected the elemental composition of its food to some extent. Food quality had a significantly negative effect on the numerical response of O. marina. Whereas N-limited R. salina and nutrient replete R. salina resulted in similar growth rates, P-limited algae had a significantly negative effect on the specific growth rate of O. marina. Hence, the lack of elemental phosphorus of O. marina feeding on P-limited algae caused a reduction in growth. Thus, despite their weaker homoeostasis, heterotrophic protists are also affected by high C:P food in a similar way to crustacean zooplankton.     

Nutritional constraints on mountain baboons (Papio ursinus): Implications for baboon socioecology

Summary Populations of baboon (Papio sp.) at geographic and climatic extremes for the genus show a tendency to one-male organization, whereas most baboons live in multimale social groups; this effect has been attributed largely to limitation of food supply, but baboons' complex diet has hindered proper nutritional analyses. To test these optimal-diet explanations of social variation, we quantified intake and used phytochemical analysis of foods to compare the nutrition, during seasonal changes, of two groups of mountain baboons (P. ursinus) living at different altitudes of a continuous grassland habitat. The majority of plant foods were eaten uniquely by one or other group, though their altitudinal separation was only 400 m, and the time budget of feeding choices varied with age-sex class as well as season. Converting to a common currency of nutrients reveals that baboons gained the same yield from a unit time spent foraging (whether this is measured in edible dry weight, or simply protein) in both groups, despite their differing mean altitude, whereas seasonal variation was large and statistically significant. Increased feeding time at the winter bottleneck made no effective compensation for the poorer food yields: in late winter there was a minimum for daily nutrient gain at both altitudes. Apparently this population is already at an extreme for the time animals devote to foraging in winter, when they rely on inconspicuous and slow-to-harvest swollen shoot bases and underground plant storage organs. Since an individual's nutrient yield does not vary with altitude, we conclude that socioecological parameters are effectively optimized for feeding. Since contest competition is absent, this adjustment of foraging efficiency is largely through the effect of differential density on scramble competition. Differences in social structure are considered to be a secondray consequence of optimal foraging, mediated through altitudinal variation in either population density or in day range limits.     

Nutrient enrichment reduces constraints on material flows in a detritus-based food web

Most aquatic and terrestrial ecosystems are experiencing increased nutrient availability, which is affecting their structure and function. By altering community composition and productivity of consumers, enrichment can indirectly cause changes in the pathways and magnitude of material flows in food webs. These changes, in turn, have major consequences for material storage and cycling in the ecosystem. Understanding mechanisms and predicting consequences of nutrient-induced changes in material flows requires a quantitative food web approach that combines information on consumer energetics and consumer-resource stoichiometry. We examined effects of a whole-system experimental nutrient enrichment on the trophic basis of production and the magnitude and pathways of carbon (C), nitrogen (N), and phosphorus (P) flows in a detritus-based stream food web. We compared the response of the treated stream to an adjacent reference stream throughout the study. Dietary composition and elemental flows varied considerably among invertebrate functional feeding groups. During nutrient enrichment, increased flows of leaf litter and amorphous detritus to shredders and gatherers accounted for most of the altered flows of C from basal resources to consumers. Nutrient enrichment had little effect on patterns of material flows but had large positive effects on the magnitude of C, N, and P flows to consumers (mean increase of 97% for all elements). Nutrient-specific food webs revealed similar flows of N and P to multiple functional groups despite an order of magnitude difference among groups in consumption of C. Secondary production was more strongly related to consumption of nutrients than C, and increased material flows were positively related to the degree of consumer-resource C:P and C:N imbalances. Nutrient enrichment resulted in an increased proportion of detrital C inputs consumed by primary consumers (from -15% to 35%) and a decreased proportion of invertebrate prey consumed by predators (from -80% to 55%). Our results demonstrate that nutrient enrichment of detritus-based systems may reduce stoichiometric constraints on material flows, increase the contribution of consumers to C, N, and P cycling, alter the proportion of C inputs metabolized by consumers, and potentially lead to reduced ecosystem-level storage of C.     

Sulfur isotopic variations in soft tissues of five benthic animals from the reductive,tidal-flat sediments in northern Kyushu,Japan

The sulfur nutrition of five benthic animals living in or on reductive, tidal-flat sediments has been studied by using the sulfur isotopic signatures of their soft tissues. The mean '³⁴S values (+6.1‰ to +13.8‰, relative to the Cañyon Diablo troilite reference) of these animals' tissues are lower than those of many common marine animals, which have values close to those of seawater sulfate-sulfur (+21‰). This indicates that these animals use a ³⁴S-depleted sulfur source, which may be derived from bacterial sulfide in the sediments (less than -20‰). The animals that inhabit such sediments are adapted to an anoxic environment, where toxic hydrogen sulfide prevails. Due to the sulfide-rich habitat, benthic animals are expected to assimilate hydrogen sulfide directly during detoxification, or to prefer a diet which has a low '³⁴S signature. Variations in '³⁴S values of the sampled molluscs were fairly small, whereas migratory shrimp and fish tended to have larger variations, implying that migratory animals feed on diverse prey, while the molluscs feed on a common food, or their assimilative capacity for sulfide-sulfur does not vary among individuals. A gastropod inhabiting the surface of the reductive sediment showed a distinctively low '³⁴S value (+5.8‰ to +6.4‰), indicating that the animal fed on detritus from reeds and halophytes with low '³⁴S values (-19.1‰ to -2.1‰). This study suggests that some benthic animals incorporate sulfide-sulfur for their nutrition and that sulfur isotope composition can be a useful indicator in the analysis of the food habitat of animals.     

The effects of seston food quality on planktonic food web patterns

In planktonic food webs, the conversion rate of plant material to herbivore biomass is determined by a variety of factors such as seston biochemical/elemental composition, phytoplankton cell morphology, and colony architecture. Despite the overwhelming heterogeneity characterizing the plant–animal interface, plankton population models usually misrepresent the food quality constraints imposed on zooplankton growth. In this study, we reformulate the zooplankton grazing term to include seston food quality effects on zooplankton assimilation efficiency and examine its ramifications on system stability. Using different phytoplankton parameterizations with regards to growth strategies, light requirements, sinking rates, and food quality, we examined the dynamics induced in planktonic systems under varying zooplankton mortality/fish predation, light conditions, nutrient availability, and detritus food quality levels. In general, our analysis suggests that high food quality tends to stabilize the planktonic systems, whereas unforced oscillations (limit cycles) emerge with lower seston food quality. For a given phytoplankton specification and resource availability, the amplitude of the plankton oscillations is primarily modulated from zooplankton mortality and secondarily from the nutritional quality of the alternative food source (i.e., detritus). When the phytoplankton community is parameterized as a cyanobacterium-like species, conditions of high nutrient availability combined with high zooplankton mortality led to phytoplankton biomass accumulation, whereas a diatom-like parameterization resulted in relatively low phytoplankton to zooplankton biomass ratios highlighting the notion that high phytoplankton food quality allows the zooplankton community to sustain relatively high biomass and to suppress phytoplankton biomass to low levels. During nutrient and light enrichment conditions, both phytoplankton and detritus food quality determine the extent of the limit cycle region, whereas high algal food quality increases system resilience by shifting the oscillatory region towards lower light attenuation levels. Detritus food quality seems to regulate the amplitude of the dynamic oscillations following enrichment, when algal food quality is low. These results highlight the profitability of the alternative food sources for the grazer as an important predictor for the dynamic behavior of primary producer–grazer interactions in nature.     

Role of the fish Astyanax aeneus (Characidae) as a keystone nutrient recycler in low-nutrient neotropical streams

Nutrient recycling by animals is a potentially important biogeochemical process in both terrestrial and aquatic ecosystems. Stoichiometric traits of individual species may result in some taxa playing disproportionately important roles in the recycling of nutrients relative to their biomass, acting as keystone nutrient recyclers. We examined factors controlling the relative contribution of 12 Neotropical fish species to nutrient recycling in four streams spanning a range of phosphorus (P) levels. In high-P conditions (135 microg/L soluble reactive phosphorus, SRP), most species fed on P-enriched diets and P excretion rates were high across species. In low-P conditions (3 microg/L SRP), aquatic food resources were depleted in P, and species with higher body P content showed low rates of P recycling. However, fishes that were subsidized by terrestrial inputs were decoupled from aquatic P availability and therefore excreted P at disproportionately high rates. One of these species, Astyanax aeneus (Characidae), represented 12% of the total population and 18% of the total biomass of the fish assemblage in our focal low-P study stream but had P excretion rates > 10-fold higher than other abundant fishes. As a result, we estimated that P excretion by A. aeneus accounted for 90% of the P recycled by this fish assemblage and also supplied approximately 90% of the stream P demand in this P-limited ecosystem. Nitrogen excretion rates showed little variation among species, and the contribution of a given species to ecosystem N recycling was largely dependent upon the total biomass of that species. Because of the high variability in P excretion rates among fish species, ecosystem-level P recycling could be particularly sensitive to changes in fish community structure in P-limited systems.     

Food regulates reproduction differently in different habitats: experimental evidence in the Goshawk

Food supplementation experiments have been widely used to get detailed insight into how food supply contributes to the reproductive performance of wild animals. Surprisingly, even though food seldom is distributed evenly in space, variation in local habitat quality has usually not been controlled for in food supplementation studies. With results from a two-year feeding experiment involving a habitat-sensitive avian top predator, the Northern Goshawk Accipiter gentilis, we show that treatment effects on goshawk reproductive performance are habitat dependent. Extra food reduced nestling mortality in low-quality territories where prime habitat (forest) is scarce, but not in high-quality territories where prime habitat is abundant. Consequently, brood size did not differ between treatment categories in heavily forested territories, but fledgling numbers differed between unfed and fed goshawk pairs breeding in territories where forest is scarce. However, because extra food was not superabundant, this artificial increase in offspring number induced a dramatic decrease in nestling condition in low-quality territories. Treatment effects were detected even after controlling statistically for other potentially confounding effects (year, territory identity) and strongly covaried with territory-specific abundances of the most important summer prey species. These results highlight the importance of acknowledging the effect that small-scale variation in habitat quality and availability of natural food may have on the results of food supplementation experiments. In order to assess the generality of food supplementation effects, the integration of habitat heterogeneity and variation in food abundance is thus needed, especially among species in which small-scale variation in habitat quality influences demographic patterns.     

The Potential Impact of Geophagia on the Bioavailability of Iron, Zinc and Calcium in Human Nutrition

Geophagia, the deliberate ingestion of soil, is a complex eating behaviour with obscure aetiology and numerous health/medical problems. It is conventionally assumed that geophagia may help supplement mineral nutrients in individuals with limited intake of trace elements such as Fe and Zn. This view, however, has largely been based on the bulk nutrient composition of geophagic materials and the assumption that these nutrients are potentially available for absorption in the body. We have tested this assumption by equilibrating five geophagic materials collected from Uganda, Tanzania, Turkey and India with mineral nutrient concentrations and conditions similar to the gastrointestinal tract. The results showed that all five geophagic materials, regardless of their composition, sorbed large amounts of Fe and Zn across a range of dietary intake scenarios, even under acidic conditions (pH 2) similar to the stomach. However, significant amounts of Ca desorption were observed from calcareous soil samples. The findings show that while calcareous geophagic materials may supplement Ca, geophagia can potentially cause Fe- and Zn-deficiency. This is consistent with mineral nutrient deficiency problems observed in clinical nutrition studies conducted amongst geophagic populations.     

三江平原退化湿地和农田土壤养分的比较研究

三江平原农业开垦导致地表水位和土壤水分下降,原生湿地退化为沼泽化草甸和典型草甸,或者直接转化为水田和旱田.退化湿地与农田土壤养分的对比研究结果表明,4种样地类型0-30 cm土层土壤有机质含量为水田＞沼泽化草甸＞旱田＞典型草甸,全氮含量差异与有机质含量差异相一致,速效磷含量为水田＞旱田＞沼泽化草甸＞典型草甸.这说明在湿地退化为典型草甸的过程中土壤养分严重下降,水分状况是影响湿地土壤养分下降的关键因素;但是农田土壤养分仍然保持较高水平,主要是由于耕作、施肥等非水分因素的影响.由此可见,水分条件和人为干扰共同决定了退化湿地和农田土壤养分状况.     

Aluminium and calcium in soil and food from Guam,Palau and Jamaica: Implications for amyotrophic lateral sclerosis and parkinsonism-dementia syndromes of Guam

Low calcium and high aluminium concentrations in the soils, waters and native foods have been hypothesised as environmental factors contributing to the unusually high incidence of amyotrophic lateral sclerosis and parkinsonism with dementia (ALS-PD) found on the island of Guam. The amounts of elemental aluminium and calcium were measured in foods of the native diet of the Chamorro people of Guam. The amount of aluminium eluted from topsoil by water at pH 7 at 22 °C was also measured. For comparison, food, water and soil samples were collected from two islands which have not reported a high incidence of ALS-PD syndromes: Palau and Jamaica.Compared with agricultural soils of Jamaica or Palau, the agricultural soils of Guam averaged 42-fold higher yield of elutable aluminium. The food data, however, do not indicate a differentially high exposure to elemental aluminium or low calcium intake in the diet of any one population. While this study did not detect an unusually high dietary aluminium or low dietary calcium content, the soils and possibly the dusts of Guam may be a major source of aluminium entering the body of the native people, particularly through the respiratory epithelium. Since iipid soluble organic ligands of aluminium more readily penetrate epithelial membranes, further study of soil aluminium ligands is required.     

Bromeliad-living spiders improve host plant nutrition and growth

Although bromeliads are believed to obtain nutrients from debris deposited by animals in their rosettes, there is little evidence to support this assumption. Using stable isotope methods, we found that the Neotropical jumping spider Psecas chapoda (Salticidae), which lives strictly associated with the terrestrial bromeliad Bromelia balansae, contributed 18% of the total nitrogen of its host plant in a greenhouse experiment. In a one-year field experiment, plants with spiders produced leaves 15% longer than plants from which the spiders were excluded. This is the first study to show nutrient provisioning in a spider-plant system. Because several animal species live strictly associated with bromeliad rosettes, this type of facultative mutualism involving the Bromeliaceae may be more common than previously thought.     

Association of minor and trace elements with mineralogical constituents of urinary stones: A hard nut to crack in existing studies of urolithiasis

The role of metals in urinary stone formation has already been studied in several publications. Moreover, urinary calculi can also be used for assessing exposure of humans to minor and trace elements in addition to other biological matrices, for example, blood, urine, or hair. However, using urinary calculi for biomonitoring of trace elements is limited by the association of elements with certain types of minerals. In this work, 614 samples of urinary calculi were subjected to mineralogical and elemental analysis. Inductively coupled plasma mass spectrometry and thermo-oxidation cold vapor atomic absorption spectrometry were used for the determination of major, minor, and trace elements. Infrared spectroscopy was used for mineralogical analysis, and additionally, it was also employed in the calculation of mineralogical composition, based on quantification of major elements and stoichiometry. Results demonstrate the applicability of such an approach in investigating associations of minor and trace elements with mineralogical constituents of stones, especially in low concentrations, where traditional methods of mineralogical analysis are not capable of quantifying mineral content reliably. The main result of this study is the confirmation of association of several elements with struvite (K, Rb) and with calcium phosphate minerals, here calculated as hydroxylapatite (Na, Zn, Sr, Ba, Pb). Phosphates were proved as the most important metal-bearing minerals in urinary calculi. Moreover, a significantly different content was also observed for Fe, Zr, Mo, Cu, Cd, Se, Sn, and Hg in investigated groups of minerals. Examination of such associations is essential, and critical analysis of mineral constituents should precede any comparison of element content among various groups of samples.     

Nebenprodukte der Lebensmittelverarbeitung als Futtermittel

The use of byproducts of the food industry as feedstuffs for animals has become a significant conflict for agriculture. Public regulations concerning the improvement of nutrient recycling and economic production with less financial support, on one hand, and the avoidance of all risks for human and animal health, on the other hand, are seen to affect agriculture practice. In this paper, information is presented about the quantities and quality of byproducts of the food industry used as feedstuffs. Also the nutritional and economical value of meat meal is discussed including ecological aspects. Other use or the disposal of products high in their nutritional value should, in the future, be no alternatives to the use as feed for animals, when risks are carefully controlled, because of the necessity for a sustainable agriculture and economy.     

Dynamic stoichiometric response to food quality fluctuations in the heterotrophic dinoflagellate Oxyrrhis marina

With respect to nutrients, plants are rather non-homoeostatic while most metazoans have much more confined ranges of nutrient ratios. It was recently highlighted that the homoeostatic ability of microzooplankters lies in between these two extremes. Nevertheless, we know very little on the dynamics of stoichiometric changes. Hence, we investigated how the stoichiometry of the heterotrophic dinoflagellate Oxyrrhis marina is affected (1) during a starvation period and (2) when fed nutrient deplete Rhodomonas salina after having been pre-conditioned on nutrient replete algae and vice versa. We observed that the dinoflagellate was able to maintain its N:P ratio constant over 78 h of starvation. We inferred that under starvation, nitrogen-limited O. marina mainly used fat as energy source while nitrogen-rich individuals also used proteins as fuel in cellular respiration. Further, we showed that O. marina presents resistance to nutrient limitation, with stronger regulation against P-limitation than against N-limitation. This resilience in microzooplankton stoichiometry following food quality stress would have great implications for both top-down (nutrient remineralisation) and bottom-up controls (quality as food).     

Nutrient Limitation of Marine Microbial Production: Fact or Artefact?

The popular view of marine phototrophic (“primary”) production being limited by nutrient availability is questioned because of inbuilt faults in experiment design and ossible errors in incorporation of inorganic nutrients, especially of NO;. These events are typical of immature ecosystems in which nutrient cycling is poorly developed. Microbial loop production is tightly coupled with average zero net production and low levels, but high fluxes, of key nutrients. Moreover, experimental methods may interfere with microbial processes creating artefacts and resulting in a diagnosis of nutrient deprivation. interpretation. There appears to be a preoccupation with high net rates of Y¹⁴CO₂-tixation and incorporation of inorganic nutrients, especially of NO₃. These events are typical of immature ecosystems in which nutrient cycling is poorly developed. Microbial loop production is tightly coupled with average zero net production and low levels, but high fluxes, of key nutrients. Moreover, experimental methods may interfere with microbial processes creating artefacts and resulting in a diagnosis of nutrient deprivation.