5 and rapid, accurate, sample analysis (Michener and Schell, 1994; Dittel et al., 1997; Verschoor et al., 2005). Adaptation of a similar approach to the scale of larval nutrition is attractive to circumvent some of the difficulties associated with assessment of ingestion and assimilation in such small and fast-changing life stages, with direct measurement of nutrient incorporation rather than use of indirect indices or added tracers. Hatchery systems are highly amenable to this approach, as they represent very controlled mesocosms with a limited number of food sources and short planktonic food chains with rapid and measurable bioaccumulation of the heavier stableisotopes of carbon and nitrogen at each trophic step. This paper reviews the current use of natural stableisotopes in larval nutrition research, compared to enriched stable isotope and radio-labeled tracers, and proposes a range of potentially valuable extensions of these applications in future studies.
Different techniques have been used to estimate assimilation in aquatic organisms. Indirect methods may use indigestible markers such as ash or chromic oxide measured in food and faeces to determine apparent assimilation efficiency (Conover, 1966; Bordner et al., 1983; Goodman-Lowe et al., 1999), assessment of energy loss as excretory products (Drazen et al., 2007) or determining the elemental composition of ingested food sampled from different segments of the digestive tract (Quinn, 1986). The availability of purified radio-isotopes allows tracing of isotope-labelled nutrients within organisms, enabling estimation of ingestion, assimilation and respiration rates by direct rather than indirect methods (e.g. Britz, et al., 1997; Lu et al., 2006). However, the use of radioactive isotopes is subject to a number of safety regulations (Schlechtriem et al., 2004) and the dilution factor is relatively fast, so their use is generally limited to short-term tracing of dietary components. In contrast, stableisotopes are non-hazardous, non-invasive and the changing ratio of stableisotopes in tissues can be used to determine the contribution of dietary sources to growth over longer periods in individuals or at the population level. Different food items have different isotopic signatures and different isotopes of the same element are incorporated in tissues at different rates, therefore in ecological studies they can be used to infer trophic linkages (Van der Zanden et al., 1998), providing an integration of feeding over time (Peterson and Fry, 1987) and also allowing the use of mixing and mass balance models to estimate the relative contribution of different food sources (Burford et al., 2004). The application of these techniques and models has also supported experimental investigation of nutrition in crustaceans, in studies using either naturally-occurring or artificially-enriched stableisotopes in compound diets (Parker et al., 1989; D’Avanzo et al., 1991; Preston et al., 1996). In an extension of ecological food web studies, naturally-occurring stableisotopes in live plankton have been used to investigate the fate of nutrients in hatchery systems where several food sources are present (Schlechtriem et al., 2004; Jomori et al., 2005; Results from Chapter 3) and to assess carbon and nitrogen turnover rates (Fry and Arnold, 1982; Hesslein et al., 1993; MacAvoy et al., 2005).
One of the most reliable methods applied to determine assimilation efficiencies is by means of isotopic assessments. Most of the elements having biologic relevance have two or more stableisotopes (for example, 12 C and 13 C for carbon, 14 N and 15 N for nitrogen). The only difference between different isotopes of the same element is the number of neutrons, which do not affect the reactive properties of such isotopes. Frequently, one of these isotopes is present at a natural abundance level much higher than the “heavy” isotope (Ehleringer & Rundel 1989); however, all participate in biochemical reactions. Animals have a tendency to accumulate the heavier isotopes due to a discriminating effect of the different enzymatic pathways preferentially incorporating the heavier isotopes, while the lighter isotopes are excreted (Martínez del Rio & Wolf 2005). This physiological effect confers specific isotopic values to organisms belonging to different trophic levels in the aquatic and terrestrial ecosystems and thus, isotopic values can be used as natural biomarkers. Isotopic values are measured by means of isotope ratio mass spectrometry (IRMS). Under this technique, the target compound must be first combusted in order to convert the elements of interest to gaseous form before introduction into the mass spectrometer. The most commonly used IRMS approaches to analyze carbon and nitrogen stableisotopes involve gas purification to introduce carbon as CO 2 and nitrogen as N 2 . The purified compounds are then
contribution in crustacean larvae using stableisotopes is difficult due to rapid ontogeny through larval stages and trophic levels, which frequently prevent the organisms form reaching isotopic equilibrium. However, as observed in the present study, the very fast growth of penaeid larvae and PL (fed on 100, 75 and 50% of Artemia nauplii) achieved isotopic equilibrium with the diets in as little as 5 d. The use of isotopic mixing models is limited when the dietary sources have overlapping isotopic profiles. Evaluation of nutrient incorporation thus requires previous knowledge (or estimation) of the diet isotopic values in order to ensure enough resolution on the isotopic changes occurring in tissue over time as a result of dietary intake. Although the use of live feeds represents clear advantages in the culture of marine larvae such as high digestibility, availability in the water column and suitability for nutritional enrichment, they are expensive to culture and provide a vector for the introduction of pathogenic micro-organisms into larval culture tanks (Southgate and Partridge, 1998), therefore, there are continuous efforts in developing and improving inert diets that can be used at higher replacement levels. In this regard, the use of stableisotopes provides an additional useful tool in assessing nutrient incorporation from
The channel catfish (Ictalurus punctatus) is a native freshwater species widely distributed in USA, Canada, and North-Eastern Mexico. This species has a wide demand and offers great potential for continued growth, the latter being reflected in an important increase in global production in the last 30 years from 100,000 to 500,000 ton per year (FAO, 2015). Catfish farming represents an important activity in Mexico and it is supported by a constant hatchling production throu- ghout the year, which is a key factor to supply demand for catfish producers (Lara-Rivera et al., 2015). Estimated protein requirements of channel catfish vary between 25 to 45%, depending on the growing conditions and the size of the organism (López et al., 2002). Catfish diets thus require to be formulated with ingredients having good protein content and acceptable nutritional characteristics, in particular for the earlier life stages. On the other hand, there is a wide variety of nutritional techniques that have been used to evaluate new dietary formulations. Frequently applied methods include those estimating the palatability of nutrients and the apparent digestibility, the latter by means of inert tracers (Jia et al., 2005; Venou et al., 2009). Other evaluation methods are represented by the assessment of energy balances (Ye et al., 2009) and the determination of nutritional conditions using molecular markers (Benedito-Palos et al., 2014). All these techniques allow evaluating the nutritional perfor- mance of a diet or test ingredient. Relatively recent nutritional studies have included the use of stableisotopes to estimate the physiological utilization of nutrients provided by alternative ingredients. Studies applying such methodologies generate relevant information on the suitability of new feedstuffs for aquaculture nutrition. Diverse isotopic techniques have been adopted from ecological studies that employ the relative ratios of carbon stableisotopes ( 13 C/ 12 C,
5b, 5d, 5e). Opaque grains partly replace bioclasts and matrix and line wavy stylolites (Figures 5b, 5d, 5e). The opaque material is a dull grayish-yellow color suggestive of leucoxene, and higher in the section it has the silvery color of hematite and in the upper samples pyrite is present. Stress lineations are thin elongate subparallel calcite string- ers (Figures 5e, 5f) that parallel stylolites. In the upper three samples, dolomite euhedra are scattered across the matrix and replace bioclasts and intrude chert crystals, lineations and stylolites (Figures 5c, 5d). The dolomite has a golden color suggesting that it may be iron-rich, and in places dolomite includes opaque red-brown hematitic material. The resolvable paragenetic succession is: 1) encrustation of bioclasts by cyanobacteria resulting in micritic films and borings; 2) formation of opaque iron-bearing minerals; 3) recrystallization of micrite matrix; 4) chert partly replacing shells and locally matrix; 5) burial and forma- tion of stylolites and calcite stress lineations; and 6) crystallization of fe-rich dolomite euhedra; and 7) alteration of iron-bearing minerals. Stableisotopes
A method traditionally employed for studying the diets of invertebrates is the analysis of gut contents since it usually represents the type of food available in the environment (Allan and Castillo, 2007). However, this method presents some disaventages such as the impossibility to determine certain food categories when digestion process is advanced or consider a food item as prey when it was accidentally acquired during the feeding act. Therefore, the use of stableisotopes constitutes a key tool to discern trophic ecological process. The analysis of the tissues using this technique allows to consider only the assimilated food sources. Moreover, unlike gut content analysis, it integrates functional responses over time. The stable-N isotopic signature (δ 15 N) in particular, is used to determine the
Our study provides a better understanding of the role of R. darwinii in the austral temperate forests of South America. The results of the trophic position of R. darwinii revealed their importance in the transfer of nutrients along the food chain, linking low trophic positions with intermediate predators. Although we provided information on the food web structure of R. darwinii, it is important for future studies to expand the spectrum of studied species to higher trophic positions to integrate potential predators (e.g. birds or reptiles) or other species of anurans sympatric to R. darwinii, as well as to lower trophic levels to compre- hend the variety of primary producers in this trophic system. The use of stableisotopes provides a robust methodology to determine ingested and assimilated food, as well as information on the trophic position of the species under study (Davis et al. 2012). The use of SIA enables us to obtain relevant dietary informa- tion, and together with complementary data (i.e. stomach content analysis and prey availability), is a recommended approach when working with highly threatened and cryptic species, from which speci- mens can be difficult to obtain (Gillespie 2013).
Abstract: Stable isotope studies of elements in biological organisms have become a useful tool to assess the exchange of mole- cules in the biosphere. Since water is one of the most abundant molecules in such an exchange, studies on stableisotopes of hydrogen and oxygen have become a fundamental component of many plant ecophysiological studies, from the leaf level to the reconstruction of past climates. In this review, we mention the most common methodologies, general notation and the most rel- evant research on hydrogen and oxygen stableisotopes. Also, we discuss studies on plant water sources, leaf isotopic enrichment due to transpiration, the relationship between environment and oxygen stableisotopes in organic matter, and present studies that propose some plant species as environmental indicators in a globally changing world.
The cave bear presents a specific tooth morphology with wide grinding surfaces, and muscle insertions in the skull and the jaw which show a great biting power, which is the reason why it is thought to follow a basically herbivorous diet (KURTÉN, 1976). In recent years, diffe- rent approaches have been followed as to the reconstruction of this species´ diet through the analysis of stableisotopes, usually 13 C and 15 N, preferably in bone
ical evidence to propose an explanation of how T. landbeckii dunes form. Contrary to wind‐blown dunes, the systems studied here actually grow against the main wind direction, which would explain their unusual layered stratigraphy. We also examined a number of parameters preserved in the buried T. landbeckii layers, including stable carbon and nitrogen isotopes. Stratigraphic and stable carbon isotope evidence clearly points to a link between T. landbeckii leaf burial and the generation of distinct “cap” carbonates. This process occurs in a similar fashion to the development of soil carbonate but instead of precipitation of biologi- cally respired CO 2 , we suspect that oxidation of calcium
5 (Phillips, 2012). In aquaculture nutrition, the isotopic values of carbon and nitrogen have been used as natural biomarkers to estimate dietary contributions in organisms fed on experimental dietary formulations having ingredients with contrasting isotopic signatures (Martínez-Rocha et al., 2013; Gamboa-Delgado et al., 2013, 2014). The different dietary resources found in aquatic and terrestrial ecosystems frequently show distinct δ 15 N values due to the effect of characteristic nutrient flows and metabolic pathways. However, this natural flow of nutrients (and isotopes) is altered under the controlled, artificial systems promoting the growth of commercial valuable microorganisms from specific substrates. The present study employed the isotopic differences found in torula yeast and fish meal to assess the relative incorporation of dietary nitrogen and total dry matter supplied by these sources to the growth of Pacific white shrimp by means of an isotope mixing model.
In the present study, a significant correlation between stableisotopes and ecomophology was observed, in contrast to the latter and diet content. In this respect, diet analysis provides a snapshot of fish feed- ing habits and shows temporal variations that could be difficult to ap- proach. Stableisotopes analysis provides a time- integrated indicator of energy resources (Vander Zanden, Casselman, & Rasmussen, 1999). When combined, these two sources of evidence provide robust ana- lytic tools that can be used to better understand the consumption and assimilation of food by fish (Vander Zanden & Vadeboncoeur, 2002). Stable carbon and nitrogen isotope ratios have been widely used to provide a time- integrated perspective of feeding relationships (Vander Zanden, Casselman, et al., 1999). The nitrogen stable isotope signature ( δ 15 N) increases proportionally to the trophic position in the food web
Limpets (N. deaurata and N. magellanica) were randomly collected from an intertidal boulder- cobble field at Bahía Laredo located in the eastern part of the Strait of Magellan (52°56.5´S; 70°50´W). N. deaurata is abundant in the lower intertidal zone while N. magellanica is present in the middle and upper intertidal zone. Sampling for gut content analysis was carried out during 2008/2009. Ten individuals of each species were hand-picked, preserved in 4% formaldehyde-seawater solution, placed in labeled plastic bags and transported to the laboratory at the Instituto de la Patagonia (Universidad de Magallanes) in Punta Arenas, Chile. Sampling for stableisotopes analysis was performed between January and February 2009 (austral summer). Five individuals for each species were collected and placed in labeled plastic bags and transported frozen to the laboratory at the Instituto de la Patagonia where they were stored at -20 °C prior to analysis at the Alfred Wegener Institute (AWI), Germany.
authors did not provide the stratigraphic context of their specimens. Carbon and oxygen stableisotopes in molars of D. mexicanus and N. eurystyle from the Tecolotlán basin have not previously been analyzed. In the present study, enamel from the molar of an individual from each species from Tecolotlán basin was analyzed and the data were compared with those from the molar of an individual of each species from Rancho El Ocote. The objective was to detect differences and similarities in diet of the two species in comparison with the results recorded by MacFadden (2008).
The isotopes (or nuclides) are classified as stable and radioactive (radioisotopes or radionuclides) that undergo radioactive decay. For instance, both the 12 C and 13 C are considered as stableisotopes, while the 14 C is a radioactive form of carbon. When an element has no stable isotope(s), then the atomic mass of its less unstable (most “stable”) isotope is shown in parentheses in the periodic table. Thus, some elements are represented by a stable isotope, others by a radioactive one, and yet others by both. Usually, the most abundant isotopes of a particular element in the nature are usually the stable ones. Yet, many isotopes classified as stable are predicted to be radioactive, albeit with extremely long half-lives. For instance, 35 primordial nuclides (present at the formation of the solar system; ~4.6 milliards of years ago) have extremely long half-lives (more than 80 million years). There are 27 radionuclides with predicted half-lives longer than the age of the universe (~13.75 milliards of years). Extremely long-lived radioisotopes are the tellurium, indium, and rhenium. For instance, the 128 Te has the longest half-life among the radionuclides, being about 160 x 10 12 times the age of the universe. Besides, if the proton decay is considered, all elements would be ultimately unstable, given enough time. Yet, the stable/unstable classification is used for practical reasons. On the other hand, the radiogenic nuclides (which can be stable or radioactive) are the ones being generated during the radioactive decay processes.
Nehari’s result is well known in the area of systems and control (). It produces, both for discrete and continuous time systems, the optimal stable projection of a completely unstable system. Furthermore, the optimality implies that the resulting error is an all–pass ﬁlter with a gain corresponding to the highest Hankel singular value of the original system. It can be stated as follows: