Christopher Izzo

Strontium randomly substituting for calcium in fish otolith aragonite

The chemistry of fish ear bones (otoliths) is used to address fundamental questions in fish ecology and fisheries science. It is assumed that strontium (Sr), the most important element used in otolith chemistry research, is bound within the aragonitic calcium carbonate lattice of otoliths via random chemical replacement of calcium; however, this has never been tested and three other alternatives exist with regard to how Sr may be incorporated. If any variation in the mode of incorporation occurs, otolith chemistry data may be misinterpreted, impacting how fish and fisheries are understood and managed. Using X-ray absorption spectroscopy (specifically, analysis of extended X-ray absorption fine structure or EXAFS), we investigated how Sr is incorporated within fish otoliths from seven species collected from a range of aquatic environments. For comparison, aragonitic structures from other aquatic taxa (cephalopods and coral) were also analyzed. The results consistently indicated for all samples that Sr randomly replaces Ca within the aragonite lattice. This research explicitly shows how Sr is bound within otoliths and validates a fundamental and long-held assumption in aquatic research.

Partial migration: growth varies between resident and migratory fish

Partial migration occurs in many taxa and ecosystems and may confer survival benefits. Here, we use otolith chemistry data to determine whether fish from a large estuarine system were resident or migratory, and then examine whether contingents display differences in modelled growth based on changes in width of otolith growth increments. Sixty-three per cent of fish were resident based on Ba : Ca of otoliths, with the remainder categorized as migratory, with both contingents distributed across most age/size classes and both sexes, suggesting population-level bet hedging. Migrant fish were in slightly better condition than resident fish based on Fultons K condition index. Migration type (resident versus migratory) was 56 times more likely to explain variation in growth than a model just incorporating year- and age-related growth trends. While average growth only varied slightly between resident and migratory fish, year-to-year variation was significant. Such dynamism in growth rates likely drives persistence of both life-history types. The complex relationships in growth between contingents suggest that management of species exhibiting partial migration is challenging, especially in a world subject to a changing climate.

Long-term patterns in estuarine fish growth across two climatically divergent regions

Long-term ecological datasets are vital for investigating how species respond to changes in their environment, yet there is a critical lack of such datasets from aquatic systems. We developed otolith growth ‘chronologies’ to reconstruct the growth history of a temperate estuarine fish species, black bream (Acanthopagrus butcheri). Chronologies represented two regions in south-east Australia: South Australia, characterised by a relatively warm, dry climate, and Tasmania, characterised by a relatively cool, wet climate. Using a mixed modelling approach, we related inter-annual growth variation to air temperature, rainfall, freshwater inflow (South Australia only), and El Niño–Southern Oscillation events. Otolith chronologies provided a continuous record of growth over a 13- and 21-year period for fish from South Australia and Tasmania, respectively. Even though fish from Tasmania were sourced across multiple estuaries, they showed higher levels of growth synchronicity across years, and greater year-to-year growth variation, than fish from South Australia, which were sourced from a single, large estuary. Growth in Tasmanian fish declined markedly over the time period studied and was negatively correlated to temperature. In contrast, growth in South Australian fish was positively correlated to both temperature and rainfall. The stark contrast between the two regions suggests that Tasmanian black bream populations are more responsive to regional scale environmental variation and may be more vulnerable to global warming. This study highlights the importance of examining species response to climate change at the intra-specific level and further validates the emerging use of growth chronologies for generating long-term ecological data in aquatic systems.

Contribution of water chemistry and fish condition to otolith chemistry: comparisons across salinity environments

This study quantified the per cent contribution of water chemistry to otolith chemistry using enriched stable isotopes of strontium ((86) Sr) and barium ((137) Ba). Euryhaline barramundi Lates calcarifer, were reared in marine (salinity 40), estuarine (salinity 20) and freshwater (salinity 0) under different temperature treatments. To calculate the contribution of water to Sr and Ba in otoliths, enriched isotopes in the tank water and otoliths were quantified and fitted to isotope mixing models. Fultons K and RNA:DNA were also measured to explore the influence of fish condition on sources of element uptake. Water was the predominant source of otolith Sr (between 65 and 99%) and Ba (between 64 and 89%) in all treatments, but contributions varied with temperature (for Ba), or interactively with temperature and salinity (for Sr). Fish condition indices were affected independently by the experimental rearing conditions, as RNA:DNA differed significantly among salinity treatments and Fultons K was significantly different between temperature treatments. Regression analyses did not detect relations between fish condition and per cent contribution values. General linear models indicated that contributions from water chemistry to otolith chemistry were primarily influenced by temperature and secondly by fish condition, with a relatively minor influence of salinity. These results further the understanding of factors that affect otolith element uptake, highlighting the necessity to consider the influence of environment and fish condition when interpreting otolith element data to reconstruct the environmental histories of fish.

Fish as proxies of ecological and environmental change

Anthropogenic impacts have shifted aquatic ecosystems far from prehistoric baseline states; yet, understanding these impacts is impeded by a lack of available long-term data that realistically reflects the organisms and their habitats prior to human disturbance. Fish are excellent, and largely underused, proxies for elucidating the degree, direction and scale of shifts in aquatic ecosystems. This paper highlights potential sources of qualitative and quantitative data derived from contemporary, archived and ancient fish samples, and then, using key examples, discusses the types of long-term temporal information that can be obtained. This paper identifies future research needs with a focus on the Southern Hemisphere, as baseline shifts are poorly described relative to the Northern Hemisphere. Temporal data sourced from fish can improve our understanding of how aquatic ecosystems have changed, particularly when multiple sources of data are used, enhancing our ability to interpret the current state of aquatic ecosystems and establish effective measures to safeguard against further adverse shifts. The range of biological, ecological and environmental data obtained from fish can be integrated to better define ecosystem baseline states on which to establish policy goals for future conservation and exploitation practices.

Where do elements bind within the otoliths of fish

Otolith element analyses are used extensively to reconstruct environmental histories of fish based on the assumption that elements substitute for calcium within the CaCO3 otolith structure. However, elements may also be incorporated within the protein component of the otolith in addition to the direct substitution for calcium in the mineral component, and this could introduce errors in environmental reconstructions. The aim of the present study was to determine whether elements were incorporated into the protein or mineral components of otoliths and the relative proportion of each element in each component. Element concentrations from whole ground otoliths and the isolated protein component were quantified using solution inductively coupled plasma mass spectrometry (ICP-MS). Of the 12 elements investigated, most were found in both the proteinaceous and mineral components, but always in greater concentrations in the latter. Elements considered ‘non-essential’ to fish physiology with Ca-like properties (i.e. alkaline metals) were present in the mineral component in relatively high concentrations. Elements essential to fish physiology with smaller atomic radii than Ca (i.e. transition metals) were distributed throughout the protein and mineral components of the otolith. These findings enhance our understanding of element incorporation in the otolith and, ultimately, improve interpretations of otolith-based environmental reconstructions.

Elements and elasmobranchs: hypotheses, assumptions and limitations of elemental analysis

Quantifying the elemental composition of elasmobranch calcified cartilage (hard parts) has the potential to answer a range of ecological and biological questions, at both the individual and population level. Few studies, however, have employed elemental analyses of elasmobranch hard parts. This paper provides an overview of the range of applications of elemental analysis in elasmobranchs, discussing the assumptions and potential limitations in cartilaginous fishes. It also reviews the available information on biotic and abiotic factors influencing patterns of elemental incorporation into hard parts of elasmobranchs and provides some comparative elemental assays and mapping in an attempt to fill knowledge gaps. Directions for future experimental research are highlighted to better understand fundamental elemental dynamics in elasmobranch hard parts.

Variation in Telomere Length of the Common Carp, Cyprinus carpio (Cyprinidae), in Relation to Body Length

Determinations of the age structure of wild teleost populations are vital for sustainable management and conservation efforts. Yet the commonly applied increment-based ageing techniques are limited in some teleost species due to the subjectivity and interpretation of increment patterning, and destructive sampling. Here the application of telomere length as an alternate age determinate was assessed in wild caught specimens of the common carp (Cyprinus carpio). Telomere lengths were measured from muscle biopsies and fin clips using the absolute quantitative PCR method and correlated to specimen fork lengths. Measures of telomere lengths did not differ between sexes or states of sexual maturity. However, tissue type influenced telomere lengths, with telomere lengths measured in muscle biopsies significantly increasing with increased fork lengths of C. carpio. No discernable trend was seen for fin clip derived telomeres. High levels of variability in telomere length within and among size cohorts suggest that telomere length is not a suitable means of estimating the ages of C. carpio. The cross sectional design adopted here most likely masked complex telomeric dynamics at the individual level, which are influenced by intrinsic and extrinsic processes. Understanding the causative influences of these processes on the telomere lengths of C. carpio may aid in utilizing measures of telomere length as an alternate measure of an individuals condition. Nevertheless, the need remains to develop novel non-lethal fish ageing techniques to overcome limitations of the current increment-based fish ageing technique.

Analysis of vertebral chemistry to assess stock structure in a deep-sea shark, Etmopterus spinax

Analysis of vertebral chemistry to assess stock structure in a deep-sea shark, Etmopterus spinax Matthew N. McMillan, Christopher Izzo, Claudia Junge, Ole Thomas Albert, Armelle Jung, and Bronwyn M. Gillanders* Southern Seas Ecology Laboratories, DX650 418, School of Biological Sciences, University of Adelaide, Adelaide 5005, Australia Institute of Marine Research, PO Box, 9294, 6404 Tromsø, Norway Des Requins et Des Hommes (DRDH), BLP/Brest-Iroise, 15 rue Dumont d’Urville, Plouzané 29860, France *Corresponding author: Tel.: þ61 8 8313 6235; Fax: þ61 (0)8 8313 4364; Email: bronwyn.gillanders@adelaide.edu.au

Assessing growth band counts from vertebrae and dorsal-fin spines for ageing sharks: comparison of four methods applied to Heterodontus portusjacksoni

Four methods for counting growth bands using vertebrae and dorsal-fin spines of the Port Jackson shark, Heterodontus portusjacksoni, are compared. Both calcified structures presented observable growth bands, allowing cross comparison among structures for the first time in a shark species. Whole and sectioned vertebrae and dorsal fin-spines possess highly visible growth bands and intra-reader band counts resulted in similar precision indices with little systematic bias. However, inter-reader growth band count plots showed possible biases in counts from sectioned vertebrae and sectioned dorsal-fin spines. Sectioned vertebrae and whole and sectioned dorsal-fin spines produced similar growth band counts, whereas whole vertebrae produced significantly lower counts. The similar readability, precision indices, growth band counts and apparent absence of biases between counts for a single reader would indicate that sectioned vertebrae and whole and sectioned dorsal-fin spines are both potentially useful and acceptable methods for band counting. However, inter-reader comparisons are necessary to avoid acceptance of biased estimations, resulting in over- or under-estimations of age. Validation for all age classes is essential to determining accurate age estimations for this and other species.