Otolith Elemental Composition Research Articles

Elemental composition of otoliths as a discriminator of life stage and growth habitat of the European eel, Anguilla anguilla

The hypothesis that elemental composition of otoliths of the eel (Anguilla spp.) changes with life stage and growth habitat was tested in the present study. The minor elements Cl, Na, K, Mg, Ca, Sr and P in otoliths of European eels (Anguilla anguilla) were examined by using an Electron Probe Microanalyser (EPMA) equipped with wavelength dispersive spectrometers (Cameca SX-50). Yellow-stage eels were collected from coastal waters and lakes of Sweden in 1987, 1988, 1991, and 1994, with ages ranging from 5 to 18 years old. Strontium maps and profiles of Sr : Ca ratio, as well as the elver check in otoliths, were used to classify life history stages of the eels as leptocephalus, and freshwater- and seawater-resident yellow eels. Canonical score plots of the otolith elemental compositions of the freshwater-resident yellow eel were completely separated from those of leptocephalus and seawater-resident yellow eel, but the latter two partially overlapped. Strontium is the primary component in determining the discrimination, but the nutrient-related (S and P), and the physiologically controlled elements (Na and Cl), may also play an important role in the discrimination. These results indicate that multiple-elemental information can provide additional insight into the migratory environmental history of diadromous fishes.

Effect of diet on otolith composition in Pomatomus saltatrix, an estuarine piscivore

To test the hypothesis that elemental composition of otoliths (sagittae) could be influenced by differences in natural prey type, young‐of‐the‐year bluefish Pomatomus saltatrix were captured immediately after their migration from oceanic waters into mid‐Atlantic Bight estuaries and fed either shrimp, Crangon septemspinosa and Palaemonetes spp. or fish Menidia menidia under similar temperature and salinity regimes in two separate 60 day experiments. Unlimited rations of fish and shrimp prey were provided in the first experiment which led to differences in bluefish growth rate between the two prey treatments; fish prey was limited in the second experiment to ensure that growth rates of bluefish in the two prey treatments were similar. Concentrations of seven elements in bluefish otoliths were determined using solution‐based inductively coupled plasma mass spectrometry (ICPMS). There was no significant effect of diet on five of the seven elements examined (Na, Mg, K, Ca and Mn). The levels of Sr and Ba in the otoliths of shrimp‐fed bluefish, however, were significantly higher than fish‐fed bluefish in both experiments. Concentrations of Ba in shrimp‐fed bluefish otoliths were double that found in fish‐fed bluefish. The results suggest that diet can explain some of the variation in otolith chemistry previously attributed to physical and chemical properties of the water.

Reconstructing Habitat Use and Wetland Nursery Origin of Yellow Perch from Lake Superior using Otolith Elemental Analysis

The use of otolith elemental composition as a natural tag has emerged as a powerful tool for managing and understanding the ecology of marine fish populations. The approach remains relatively untested in fresh waters, so we examined its utility for reconstructing habitat use and wetland nursery origin in Lake Superior. We analyzed the otolith margin of adult yellow perch, Perca flavescens, as an indicator of recently occupied habitat, and the juvenile region of the otolith core as an indicator of nursery area. To characterize elemental fingerprints, all otolith samples were analyzed for Ca and 13 minor and trace elements using mass spectrometry. We found differences in the otolith concentrations of several elements between yellow perch inhabiting coastal wetlands and those inhabiting the adjacent nearshore waters of Chequamegon Bay. The most striking difference was the high concentration of Sr in the sagittal margins of wetland-caught fish relative to those captured in the bay. Based on differences in otolith Sr concentrations alone, fish from bay and wetland habitats could be distinguished with 100% accuracy. We also found that elemental fingerprints derived from otolith cores of adult yellow perch were similar among fish captured from wetlands adjacent to Chequamegon Bay but quite distinct for one site outside of the bay, suggesting these fish came from a separate population from those in Chequamegon Bay. Overall, these results encourage us that elemental fingerprinting techniques will be useful for estimating the relative importance of different coastal wetland habitats to wetland-dependent species in the Great Lakes.

Spatial variability of trace elements in fish otoliths: comparison with dietary items and habitat constituents in seagrass meadows

Juvenile trumpetersPelates sexlineatus, two main prey items (amphipods and polychaetes) and seagrass constituents (detritus, young and old leaves ofZostera capricorni) were collected from two sites within six estuaries, to compare the spatial variability of elemental composition (Li, Mn, Sr, Cd, Ba and Pb). Average elemental values were lower in the fish otoliths except for Sr. Significant differences in elemental composition of otoliths were detected among estuaries (Mn and Pb). Spatial differences in concentrations of Cd were found in amphipods and polychaetes; the latter also showed differences for Ba and Pb. Detritus andZ. capricornileaves showed appreciable spatial differences for most of the elements. Spatial variability between sites was generally high. There were differences in the multivariate composition of trace elements found in the otoliths of fish among estuaries. One estuary was consistently separated from the other estuaries in the ordinations. Significant correlations were detected between concentrations of Mn in otoliths and concentrations in prey,Z. capricorniand detritus. A significant relationship was also detected between Pb in otoliths and detritus. There were significant correlations between concentrations of Mn, Sr and Ba in detritus and that in otoliths. The study demonstrated that trophic transfer and habitat constituents may be considered as a potential source for some of the elemental accumulation in fish otoliths.

Temporal and spatial variability in elemental composition of otoliths: implications for determining stock identity and connectivity of populations

Interannual variability in elemental composition of otoliths may confound spatial interpretations. The elemental fingerprints of otoliths of juvenile fish were determined for fish collected from 12 to 15 estuaries in each of three consecutive recruitment years to determine temporal variation in otolith chemistry for each estuary. It was also examined whether there is overlap in elemental fingerprints of fish collected in different years and from different estuaries that may confound subsequent spatial comparisons. Significant differences in otolith chemistry were found among years for individual elements (lithium, manganese, strontium, and barium) and for multi-element fingerprints. Some estuaries showed large variation in multi-element fingerprints among years, whereas others showed little variation among years. There was some overlap of elemental fingerprints of different estuaries, but these were not always for fish collected in the same year. The significant spatial and temporal variation in elemental fingerprints meant that it was possible to confound spatial differences with temporal differences. Therefore, if the natal estuary of the adults is to be determined, a library of elemental fingerprints needs to be built up over time for each estuary rather than a single year-class of juveniles being used as the elemental fingerprint for a number of year-classes of adults.

Otolith elemental fingerprints as biological tracers of fish stocks

Specific trace elements incorporated into the growing surface of the fish otolith reflect the physical and chemical characteristics of the ambient water, although not necessarily in a simplistic manner. Since fish which spend at least part of their lives in different water masses often produce otoliths of different elemental composition, the otolith elemental composition (‘elemental fingerprint’) can serve as an environmentally induced tag of groups of fish. On the basis of isotope dilution ICPMS (ID-ICPMS) assays of nearly 2500 dissolved adult cod ( Gadus morhua) otoliths, it has become clear that cod otolith elemental fingerprints based on the elements Li, Mg, Mn, Sr and Ba are physically stable, reproducible and consistent between left and right otoliths. Highly significant differences existed among the fingerprints of all of the spawning aggregations, resulting in a characteristic marker for each aggregation. Long-term stability (4–13 years) of the fingerprints for a given spawning group was not evident, indicating that the fingerprint was not a proxy for genetic identity. However, the fingerprint was very stable over the short-term (up to 1 year), suggesting that it could serve as a seasonally stable biological tracer, or natural tag, of pre-defined groups of fish, even during situations of extensive stock mixing. As an illustration of the tracer approach, a maximum likelihood-based stock mixture analysis was applied to feeding (summer) and over-wintering stock distributions, using the fingerprints of the spring spawning aggregations as known-stock reference samples. The results of the summer stock mixture analyses suggested that the mixture analysis was accurate within 1%, while the stock mixture analysis of the over-wintering schools produced stock-specific distributions which would have been difficult to obtain using alternative approaches. While the use of elemental fingerprints as natural tags is not suited to all stock mixing situations, suitability can probably be determined beforehand on the basis of existing environmental and biological information.

Elemental composition of otoliths as a stock delineator in fishes

The elemental composition of otoliths is increasingly being examined as a means of resolving the fine scale stock and population structure of fishes. The technique has been applied to three sets of problems: (1) discriminating between marine and freshwater populations (or life history stages), (2) determining links between natal rivers or nursery areas and adult stocks, and (3) assessing population structure in marine fishes. Thus far, there are few consistent patterns in the data. Diagnostic elements differ between species and systems; experimental and correlative studies provide little support for strong environmental effects on otolith composition (other than effects of extreme differences in salinity/strontium concentrations); and the physiological mechanisms that would allow such an effect for most elements are not well documented. The area of investigation suffers from: a lack of well-established benchmark studies against which ‘reality’ of results can be assessed; small sample sizes and incomplete analysis; and non-critical evaluation of results. Two areas of research look promising: the use of marked differences between marine and freshwater fishes (or the corresponding portions of otoliths of anadromous fish) in strontium concentrations to track migrating coastal fishes, and apparently robust indications of regional structuring of some marine fish populations. The relative youthfulness of the field dictates the need for work in a number of areas, but priorities at this stage should include developing a better understanding of the physiological mechanisms that determine otolith composition and its variability, including distinguishing the effects of handling and contamination from ‘real’ composition, and validating apparent patterns of stock structure both by independent replication of results and comparisons against other sources of information, such as genetic and tagging studies. To assure data quality and form a base for corroboration of results, widespread use of certified reference materials and careful documentation of analytic procedures are essential.

Elemental composition of otoliths from Atlantic croaker along an estuarine pollution gradient

Elemental composition of otoliths from Atlantic croaker along an estuarine pollution gradient

Comparison of accuracy, precision, and sensitivity in elemental assays of fish otoliths using the electron microprobe, proton-induced X-ray emission, and laser ablation inductively coupled plasma mass spectrometry

The elemental composition of fish otoliths is of considerable interest to those who wish to reconstruct temperature, migration, or environmental histories of individual fish based on assays of the otolith growth sequence. However, reported differences in otolith elemental composition among studies may be due in part to performance differences among four of the most popular instruments for targeted elemental analysis: wavelength-dispersive electron microprobe (WD-EM), energy-dispersive electron microprobe (ED-EM), proton-induced X-ray emission (PIXE), and laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS). To rigorously compare the sensitivity, accuracy, and precision of these four analytical tools, the International Otolith Composition Experiment distributed blind-labelled real and artificial otoliths of known but varied elemental composition to eight laboratories for assay of 10 selected elements. No one instrument type was sensitive to each element, nor was any one instrument preferred for use in all assays. In general however, abundant elements such as Na and K could only be measured accurately with an electron microprobe, while the trace elements required PIXE or LA-ICPMS. Strontium could be measured with considerable accuracy and precision by WD-EM, PIXE, and LA-ICPMS. The presence of significant, and occasionally large, differences among laboratories suggests that comparisons among published studies should be made cautiously and only after appropriate calibration.

An investigation of chronological differences in the deposition of trace metals in the otoliths of two temperate reef fishes.

Inductively Coupled Plasma-Mass Spectrometry (ICP-MS) was used to determine broad scale chronological differences in the elemental composition of otoliths from two temperate reef fishes, Parma microlepis (Gunther) (Pomacentridae) and Achoerodus viridis (Steindachner) (Labridae). Estimates of a range of microconstituents (<10 μg ion per g of otolith) were obtained, including the low level constituents Ba, Co and Mn. The removal of otolith tissue by either acid digestion or diamond saw allowed the chemical composition of the centre (=early life of fish) and edge (=later life of fish) of otoliths to be accessed without detectable contamination. ICP-MS used with either of these methods can, therefore, access chronological information stored in the otoliths of fishes. Significant differences in elemental levels (e.g., Mn) were found between the otoliths of the two species of fishes and between study sites. For both Parma microlepis and Achoerodus viridis, the centre of the otolith contained less Ca than the edge. Chronological differences in trace metal composition were found when data were normalised to sample weight (e.g., Ba and Co in A. viridis), but these differences were not observed for data normalised to the Ca concentration of the otolith sample. The merits and problems associated with normalising ionic concentrations to weight, Ca concentration, or protein concentration are discussed with the conclusion that a greater understanding of the binding affinities of all the components of otoliths (organic, as well as inorganic matrices) is needed to be in a position to select either of these internal standards as appropriate for specific ions. Despite this, ICP-MS was found to be a powerful tool that can be used to determine microconstituent fingerprints in otoliths among locations and between comparable chronological sections (e.g., cores).

Effect of Water Temperature on the Elemental Composition of Otoliths from the Juvenile Japanese Flounder, Paralichthys olivaceus

Effect of Water Temperature on the Elemental Composition of Otoliths from the Juvenile Japanese Flounder, <I>Paralichthys olivaceus</I>

Experimental assessment of the effect of temperature and salinity on elemental composition of otoliths using laser ablation ICPMS

Laser ablation – inductively coupled plasma mass spectrometry (LA-ICPMS) is a new technique that can be used for the multielemental analysis of otoliths at specific loci. This method was used to sample the otoliths of Atlantic croaker (Micropogonias undulatus), reared under different constant regimes of temperature and salinity, to determine whether the elemental composition of otoliths changes ontogenetically. Each otolith was sampled at a number of loci, beginning at the center and then every 500 μm along the longest axis to near the edge; of 23 isotopes measured simultaneously at each locus, 18 were standardized to 48Ca and included in analyses. The elemental composition at otolith centers and near their edges differed significantly amongst treatments, with the effect of temperature a stronger influence. Elemental composition also varied across otoliths from within treatments, indicating endogenous effects. Ontogenetic patterns differed amongst treatments, indicating that endogenous control was mediated by the external environment. Otoliths of fish from one tank where the physical conditions were switched, showed greater variation in the multielemental signal than that resulting only from ontogenetic change. All analyses indicated that otolith formation is the product of numerous interactive exogenous and endogenous processes, including water temperature, salinity, and ontogeny.

Experimental assessment of the effect of temperature and salinity on elemental composition of otoliths using solution-based ICPMS

Retrospective determination of the early life history of fish using the microelemental analysis of their otoliths is dependent upon understanding the factors that affect this elemental composition. Here, juvenile Atlantic croaker (Micropogonias undulatus) were reared under different treatments of temperature and salinity to determine their impacts on elemental inclusion rates in otoliths. Solution-based inductively coupled plasma mass spectrometry (ICPMS) was used to measure 21 isotopes in each otolith: isotopic concentrations ranged over seven orders of magnitude, and differed significantly amongst the temperature–salinity regimes. Univariate analyses identified 13 isotopes that contributed to these multivariate differences; the influence of temperature was stronger than that of salinity. Within each treatment there was a significant relationship between otolith microchemistry and otolith size. To some extent this confounded the interpretation of the between-treatment effect of temperature. In contrast, both the otolith and somatic growth rates were similar between the two salinity treatments, indicating that differences in elemental fingerprints were unambiguously related to the salinity difference, probably a response to the elemental concentrations in the tank water. Overall the study highlighted the current poor understanding of the mechanism of contamination of otoliths by trace elements and their incorporation into the otolith microstructure.

Otolith Elemental Fingerprinting for Stock Identification of Atlantic Cod (Gadus morhua) Using Laser Ablation ICPMS

Trace element incorporation into fish otoliths varies among samples collected at different sites. If otolith elemental composition (the elemental "fingerprint") somehow reflects the characteristics of the ambient water, the elemental fingerprint of the otolith nucleus could serve as a natural marker of fish hatched at different sites. To test this hypothesis, Atlantic cod (Gadus morhua) otoliths collected from five spawning grounds in the northwest Atlantic were tested for differences in elemental and isotopic composition. Laser ablation – inductively coupled plasma mass spectroscopy (LA-ICPMS) was used to assay the concentration of 14 isotopes (nine elements) in otolith nuclei. The sensitivity of the laser ablation system exceeded that of the electron microprobe by 2–4 orders of magnitude, with an average CV of 21% for any given isotope. Most isotopic concentrations were consistent between left and right otoliths of a given fish, and most differed significantly among sample sites; there were no significant differences by age, sex, or fish length. Multivariate analyses of the elemental fingerprints resulted in significant discrimination among sample sites. While the mechanism underlying trace element incorporation into otoliths is still unclear, otolith elemental fingerprinting has the potential to become an effective and accurate means of stock identification.

Morphometry and composition of red drum otoliths: Changes associated with temperature, somatic growth rate, and age

1. 1. Size and composition of sagittal otoliths from red drum, Sciaenops ocellatus (Sciaenidae), reared at various constant temperatures were compared with otoliths from wild-caught fish. 2. 2. Uncoupling of otolith growth and somatic growth in laboratory-reared fish was evident in otolith length, area, volume, weight, density, and organic fraction. 3. 3. Fish grown at low temperatures had significantly smaller and less dense otoliths having a greater organic content than fish of the same size grown at higher temperatures. 4. 4. Changes in inorganic elements were poorly related to temperature in laboratory-reared fish. 5. 5. The effect of temperature on otolith elemental composition was small relative to the effects of age and its associated physiological changes.