Thorrold Simon R.

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Thorrold

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Simon R.

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0000-0002-1533-7517

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Transgenerational marking of embryonic otoliths in marine fishes using barium stable isotopes

(NRC Research Press, 2006-04-13) Thorrold, Simon R. ; Jones, Geoffrey P. ; Planes, Serge ; Hare, Jonathan A.

We describe a new technique for transgenerational marking of embryonic otoliths that promises significant advancements in the study of larval dispersal and population connectivity in marine fishes. The approach is based on maternal transmission of 137Ba from spawning females to egg material that is ultimately incorporated into the otoliths of embryos produced by an individual after exposure to the isotope. We injected females of a benthic-spawning clownfish (Amphiprion melanopus) and a pelagic-spawning serranid (Centropristis striata) with enriched 137BaCl2 and then reared the resulting progeny through to settlement. Barium isotope ratios in the cores of larval otoliths were quantified using laser ablation inductively coupled plasma mass spectrometry. Larval otoliths from both species contained unequivocal Ba isotope signatures over a wide range of doses (0.8–23 μg 137Ba·g female–1). Female A. melanopus continued to produce marked larvae over multiple clutches and for at least 90 days after a single injection. The ability to administer different combinations of stable Ba isotopes provides a new means of mass-marking larvae of benthic- and pelagic-spawning fishes from multiple populations over extended spawning periods.
Elemental signatures in otoliths of larval walleye pollock (Theragra chalcogramma) from the northeast Pacific Ocean

(U.S. Department of Commerce, 2004) FitzGerald, Jennifer L. ; Thorrold, Simon R. ; Bailey, Kevin M. ; Brown, Annette L. ; Severin, Kenneth P.

The objectives of this study are to determine if larval walleye pollock from different geographic localities can be distinguished based on elemental signatures in their otoliths. By analyzing sagittal otoliths with both EPMA and laser ablation ICP-MS, we hoped to identify greater differences among locations than would have been possible by using either technique in isolation. If successful, the study may provide a powerful tool for determining stock structure and tracing migration pathways of walleye pollock in the north Pacific. These data could then be used by managers of one of the world's largest single species fisheries to direct the sustainable harvest of this considerable natural resource.
Mesoscale eddies influence the movements of mature female white sharks in the Gulf Stream and Sargasso Sea

(Nature Publishing Group, 2018-05-09) Gaube, Peter ; Braun, Camrin D. ; Lawson, Gareth L. ; McGillicuddy, Dennis J. ; Penna, Alice Della ; Skomal, Gregory B. ; Fischer, Chris ; Thorrold, Simon R.

Satellite-tracking of mature white sharks (Carcharodon carcharias) has revealed open-ocean movements spanning months and covering tens of thousands of kilometers. But how are the energetic demands of these active apex predators met as they leave coastal areas with relatively high prey abundance to swim across the open ocean through waters often characterized as biological deserts? Here we investigate mesoscale oceanographic variability encountered by two white sharks as they moved through the Gulf Stream region and Sargasso Sea in the North Atlantic Ocean. In the vicinity of the Gulf Stream, the two mature female white sharks exhibited extensive use of the interiors of clockwise-rotating anticyclonic eddies, characterized by positive (warm) temperature anomalies. One tagged white shark was also equipped with an archival tag that indicated this individual made frequent dives to nearly 1,000 m in anticyclones, where it was presumably foraging on mesopelagic prey. We propose that warm temperature anomalies in anticyclones make prey more accessible and energetically profitable to adult white sharks in the Gulf Stream region by reducing the physiological costs of thermoregulation in cold water. The results presented here provide valuable new insight into open ocean habitat use by mature, female white sharks that may be applicable to other large pelagic predators.
A review of ecogeochemistry approaches to estimating movements of marine animals

(Association for the Sciences of Limnology and Oceanography, 2013-03) McMahon, Kelton W. ; Hamady, Li Ling ; Thorrold, Simon R.

Ecogeochemistry—the application of geochemical techniques to fundamental questions in population and community ecology—has been used in animal migration studies in terrestrial environments for several decades; however, the approach has received far less attention in marine systems. This review includes comprehensive meta-analyses of organic zooplankton δ13C and δ15N values at the base of the food web, dissolved inorganic carbon δ13C values, and seawater δ18O values to create, for the first time, robust isoscapes for the Atlantic Ocean. These isoscapes present far greater geographic variability in multiple geochemical tracers than was previously thought, thus forming the foundation for reconstructions of habitat use and migration patterns of marine organisms. We review several additional tracers, including trace-element-to-calcium ratios and heavy element stable isotopes, to examine anadromous migrations. We highlight the value of the ecogeochemistry approach by examining case studies on three components of connectivity: dispersal and natal homing, functional connectivity, and migratory connectivity. We also discuss recent advances in compound-specific stable carbon and nitrogen isotope analyses for tracking animal movement. A better understanding of isotopic routing and fractionation factors, particularly of individual compound classes, is necessary to realize the full potential of ecogeochemistry.
Marine dispersal scales are congruent over evolutionary and ecological time

( 2016-10) Pinsky, Malin L. ; Saenz-Agudelo, Pablo ; Salles, Océane C. ; Almany, Glenn R. ; Bode, Michael ; Berumen, Michael L. ; Andrefouet, Serge ; Thorrold, Simon R. ; Jones, Geoffrey P. ; Planes, Serge

The degree to which offspring remain near their parents or disperse widely is critical for understanding population dynamics, evolution, and biogeography, and for designing conservation actions. In the ocean, most estimates suggesting short-distance dispersal are based on direct ecological observations of dispersing individuals, while indirect evolutionary estimates often suggest substantially greater homogeneity among populations. Reconciling these two approaches and their seemingly competing perspectives on dispersal has been a major challenge. However, here we show for the first time that evolutionary and ecological measures of larval dispersal can closely agree by using both to estimate the distribution of dispersal distances. In orange clownfish (Amphiprion percula) populations in Kimbe Bay, Papua New Guinea, we found that evolutionary dispersal kernels were 17 [95% CI: 12–24] km wide, while an exhaustive set of direct larval dispersal observations suggested kernel widths of 27 [19–36] km or 19 [15–27] km across two years. The similarity between these two approaches suggests that ecological and evolutionary dispersal kernels can be equivalent, and that the apparent disagreement between direct and indirect measurements can be overcome. Our results suggest that carefully applied evolutionary methods, which are often less expensive, can be broadly relevant for understanding ecological dispersal across the tree of life.
Otolith geochemistry discriminates among estuarine nursery areas of Solea solea and S. senegalensis over time

( 2012-04) Tanner, Susanne E. ; Reis-Santos, Patrick ; Vasconcelos, Rita P. ; Franca, Susana ; Thorrold, Simon R. ; Cabral, Henrique N.

Otolith geochemistry is used increasingly as a natural tag to retrospectively determine habitat use in marine fishes. It is necessary to first conduct a thorough assessment of spatio-temporal variability before attempting to use the approach to determine estuarine residency or natal origins. In particular, knowledge of temporal variation at different scales is important when such variability may confound spatial discrimination. We assayed elements and calculated the elemental ratios to Ca (Li:Ca, Mg:Ca, Mn:Ca, Cu:Ca, Sr:Ca, Ba:Ca, Pb:Ca) in otoliths of juvenile Solea solea and Solea senegalensis, collected over several months in 2006 and 2009 in Portuguese estuaries, using laser ablation inductively coupled plasma mass spectrometry (LA ICP-MS). The elemental compositions of the otoliths varied significantly between and within years in both of the species, although the within-year variability did not interfere in spatial discrimination. The overall classification accuracy of juveniles to their estuaries of origin varied among the years and species, ranging from 71.0% to 80.1%. Established elemental signatures constitute the baseline data for future assessments of connectivity between juvenile and adult populations of the two sole species.
Connectivity dominates larval replenishment in a coastal reef fish metapopulation

( 2011-01-25) Saenz-Agudelo, Pablo ; Jones, Geoffrey P. ; Thorrold, Simon R. ; Planes, Serge

Direct estimates of larval retention and connectivity are essential to understand the structure and dynamics of marine metapopulations, and optimize the size and spacing of reserves within networks of marine protected areas (MPAs). For coral reef fishes, while there are some empirical estimates of self-recruitment at isolated populations, exchange among sub-populations has been rarely quantified. Here we used microsatellite DNA markers and a likelihood-based parentage analysis to assess the relative magnitude of self-recruitment and exchange among 8 geographically distinct sub-populations of the panda clownfish Amphiprion polymnus along 30 km of coastline near Port Moresby, Papua New Guinea. In addition, we used an assignment/exclusion test to identify immigrants arriving from genetically distinct sources. Overall, 82% of the juveniles were immigrants while 18% were progeny of parents genotyped in our focal metapopulation. Of the immigrants, only 6% were likely to be genetically distinct from the focal metapopulation, suggesting most of the connectivity is among sub-populations from a rather homogeneous genetic pool. Of the 18% that were progeny of known adults, two thirds dispersed among the 8 sub-populations and only one third settled back into natal sub- populations. Comparison of our data with previous studies suggested that variation in dispersal distances is likely to be influenced by the geographic setting and spacing of sub-populations.
Mesoscale eddies release pelagic sharks from thermal constraints to foraging in the ocean twilight zone

(National Academy of Sciences, 2019-08-06) Braun, Camrin D. ; Gaube, Peter ; Sinclair-Taylor, Tane H. ; Skomal, Gregory B. ; Thorrold, Simon R.

Mesoscale eddies are critical components of the ocean’s “internal weather” system. Mixing and stirring by eddies exerts significant control on biogeochemical fluxes in the open ocean, and eddies may trap distinctive plankton communities that remain coherent for months and can be transported hundreds to thousands of kilometers. Debate regarding how and why predators use fronts and eddies, for example as a migratory cue, enhanced forage opportunities, or preferred thermal habitat, has been ongoing since the 1950s. The influence of eddies on the behavior of large pelagic fishes, however, remains largely unexplored. Here, we reconstruct movements of a pelagic predator, the blue shark (Prionace glauca), in the Gulf Stream region using electronic tags, earth-observing satellites, and data-assimilating ocean forecasting models. Based on >2,000 tracking days and nearly 500,000 high-resolution time series measurements collected by 15 instrumented individuals, we show that blue sharks seek out the interiors of anticyclonic eddies where they dive deep while foraging. Our observations counter the existing paradigm that anticyclonic eddies are unproductive ocean “deserts” and suggest anomalously warm temperatures in these features connect surface-oriented predators to the most abundant fish community on the planet in the mesopelagic. These results also shed light on the ecosystem services provided by mesopelagic prey. Careful consideration will be needed before biomass extraction from the ocean twilight zone to avoid interrupting a key link between planktonic production and top predators. Moreover, robust associations between targeted fish species and oceanographic features increase the prospects for effective dynamic ocean management.
Environmentally mediated trends in otolith composition of juvenile Atlantic cod (Gadus morhua)

( 2015-04) Stanley, Ryan R. E. ; Bradbury, Ian R. ; DiBacco, Claudio ; Snelgrove, Paul V. R. ; Thorrold, Simon R. ; Killen, Shaun S.

We evaluated the influence of environmental exposure of juvenile Atlantic cod (Gadus morua) to inform interpretations of natal origins and movement patterns using otolith geochemistry. Laboratory rearing experiments were conducted with a variety of temperature (~ 5, 8.5 and 12 °C) and salinity (~ 25, 28.5 and 32 PSU) combinations. We measured magnesium (Mg), manganese (Mn), strontium (Sr) and barium (Ba), expressed as a ratio to calcium (Ca), using laser ablation inductively coupled plasma mass spectrometry (ICP-MS), and stable carbon (δ13C) and oxygen (δ18O) isotopes using isotope ratio monitoring mass spectrometry. Temperature and salinity significantly affected all elements and isotopes measured, with the exception of salinity on Mg:Ca. We detected significant interactions among temperature and salinity for Mn:Ca and Ba:Ca partition coefficients (ratio of otolith chemistry to water chemistry), with significant temperature effects only detected in the 32 and 28.5 PSU salinity treatments. Similarly, we detected a significant interaction between temperature and salinity in incorporation of δ13C, with a significant temperature effect except at intermediate salinity. These results support the contention that environmental mediation of otolith composition varies among species, thus limiting the ability of generalized models to infer life history patterns from chemistry. Our results provide essential baseline information detailing environmental influence on juvenile Atlantic cod otolith composition, punctuating the importance of laboratory validations to translate species-specific otolith composition when inferring in situ life histories and movements.
Diving behavior of the reef manta ray links coral reefs with adjacent deep pelagic habitats

(Public Library of Science, 2014-02-06) Braun, Camrin D. ; Skomal, Gregory B. ; Thorrold, Simon R. ; Berumen, Michael L.

Recent successful efforts to increase protection for manta rays has highlighted the lack of basic ecological information, including vertical and horizontal movement patterns, available for these species. We deployed pop-up satellite archival transmitting tags on nine reef manta rays, Manta alfredi, to determine diving behaviors and vertical habitat use. Transmitted and archived data were obtained from seven tagged mantas over deployment periods of 102–188 days, including three recovered tags containing 2.6 million depth, temperature, and light level data points collected every 10 or 15 seconds. Mantas frequented the upper 10 m during daylight hours and tended to occupy deeper water throughout the night. Six of the seven individuals performed a cumulative 76 deep dives (>150 m) with one individual reaching 432 m, extending the known depth range of this coastal, reef-oriented species and confirming its role as an ecological link between epipelagic and mesopelagic habitats. Mean vertical velocities calculated from high-resolution dive data (62 dives >150 m) from three individuals suggested that mantas may use gliding behavior during travel and that this behavior may prove more efficient than continuous horizontal swimming. The behaviors in this study indicate manta rays provide a previously unknown link between the epi- and mesopelagic layers of an extremely oligotrophic marine environment and provide evidence of a third marine species that utilizes gliding to maximize movement efficiency.
High connectivity among locally adapted populations of a marine fish (Menidia menidia)

(Ecological Society of America, 2010-12) Clarke, Lora M. ; Munch, Stephan B. ; Thorrold, Simon R. ; Conover, David O.

Patterns of connectivity are important in understanding the geographic scale of local adaptation in marine populations. While natural selection can lead to local adaptation, high connectivity can diminish the potential for such adaptation to occur. Connectivity, defined as the exchange of individuals among subpopulations, is presumed to be significant in most marine species due to life histories that include widely dispersive stages. However, evidence of local adaptation in marine species, such the Atlantic silverside, Menidia menidia, raises questions concerning the degree of connectivity. We examined geochemical signatures in the otoliths, or ear bones, of adult Atlantic silversides collected in 11 locations along the northeastern coast of the United States from New Jersey to Maine in 2004 and eight locations in 2005 using laser ablation inductively coupled plasma mass spectrometry (ICP-MS) and isotope ratio monitoring mass spectrometry (irm-MS). These signatures were then compared to baseline signatures of juvenile fish of known origin to determine natal origin of these adult fish. We then estimated migration distances and the degree of mixing from these data. In both years, fish generally had the highest probability of originating from the same location in which they were captured (0.01–0.80), but evidence of mixing throughout the sample area was present. Furthermore, adult M. menidia exhibit highly dispersive behavior with some fish migrating over 700 km. The probability of adult fish returning to natal areas differed between years, with the probability being, on average, 0.2 higher in the second year. These findings demonstrate that marine species with largely open populations are capable of local adaptation despite apparently high gene flow.
Accelerator mass spectrometry 14C determination in CO2 produced from laser decomposition of aragonite

( 2008-08-29) Rosenheim, Brad E. ; Thorrold, Simon R. ; Roberts, Mark L.

Determination of 14C in aragonite (CaCO3) decomposed thermally to CO2 using an yttrium‐aluminum‐garnet doped neodymium laser is reported. Laser decomposition accelerator mass spectrometer (LD‐AMS) measurements reproduce AMS determinations of 14C from conventional reaction of aragonite with concentrated phosphoric acid. The lack of significant differences between these sets of measurements indicate that LD‐AMS radiocarbon dating can overcome the significant fractionation that has been observed during stable isotope (C and O) laser decomposition analysis of different carbonate minerals. The laser regularly converted nearly 30% of material removed to CO2 despite being optimized for ablation, where laser energy breaks material apart rather than chemically altering it. These results illustrate promise for using laser decomposition on the front‐end of AMS systems that directly measure CO2 gas. The feasibility of such measurements depends on 1. the improvement of material removal and/or CO2 generation efficiency of the laser decomposition system and 2. the ionization efficiency of AMS systems measuring continuously flowing CO2.
Tracing carbon flow through coral reef food webs using a compound-specific stable isotope approach

( 2015-11) McMahon, Kelton W. ; Thorrold, Simon R. ; Houghton, Leah A. ; Berumen, Michael L.

Coral reefs support spectacularly productive and diverse communities in tropical and sub26 tropical waters throughout the world’s oceans. Debate continues, however, on the degree to which reef biomass is supported by new water column production, benthic primary production, and recycled detrital carbon. We coupled compound-specific δ13C analyses with Bayesian mixing models to quantify carbon flow from primary producers to coral reef fishes across multiple feeding guilds and trophic positions in the Red Sea. Analyses of reef fishes with putative diets composed primarily of zooplankton (Amblyglyphidodon indicus), benthic macroalgae (Stegastes nigricans), reef-associated detritus (Ctenochaetus striatus), and coral tissue (Chaetodon trifascialis) confirmed that δ13C values of essential amino acids from all baseline carbon sources were both isotopically diagnostic and accurately recorded in consumer tissues. While all four source end-members contributed to the production of coral reef fishes in our study, a single source end-member often dominated dietary carbon assimilation of a given species, even for highly mobile, generalist top predators. Microbially-reworked detritus was an important secondary carbon source for most species. Seascape configuration played an important role in structuring resource utilization patterns. For instance, L. ehrenbergii, showed a significant shift from a benthic macroalgal food web on shelf reefs (71 ± 13% of dietary carbon) to a phytoplankton-based food web (72 ± 11%) on oceanic reefs. Our work provides insights into the roles that diverse carbon sources play in the structure and function of coral reef ecosystems and illustrates a powerful fingerprinting method to develop and test nutritional frameworks for understanding resource utilization.
Variation in Serripes groenlandicus (Bivalvia) growth in a Norwegian high-Arctic fjord : evidence for local- and large-scale climatic forcing

( 2006-03-03) Ambrose, William G. ; Carroll, Michael L. ; Greenacre, Michael ; Thorrold, Simon R. ; McMahon, Kelton W.

We examined the growth rate of the circumpolar Greenland Cockle (Serripes groenlandicus) over a period of 20 years (1983-2002) from Rijpfjord, a high-Arctic fjord in northeast Svalbard (80º10´N, 22°15´E). This period encompassed different phases of large-scale climatic oscillations with accompanying variations in local physical variables (temperature, atmospheric pressure, precipitation, sea ice cover), allowing us to analyze the linkage between growth rate, climatic oscillations, and their local physical and biological manifestations. Standard Growth Index (SGI), an ontogenetically-adjusted measure of annual growth, ranged from a low of 0.27 in 2002 up to 2.46 in 1996. Interannual variation in growth corresponded to the Arctic Climate Regime Index (ACRI), with high growth rates during the positive ACRI phase characterized by cyclonic ocean circulation and a warmer and wetter climate. Growth rates were influenced by local manifestations of the ACRI: positively correlated with precipitation and to a lesser extent negatively correlated with atmospheric pressure. A multiple regression model explains 65% of the variability in growth rate by the ACRI and precipitation at the nearest meteorological station. There were, however, complexities in the relationship between growth and physical variables, including an apparent 1-year lag between physical forcing changes and biological response. Also, when the last 4 years of poor growth are excluded, there is a very strong negative correlation with ice cover on a pan-arctic scale. Our results suggest that bivalves, as sentinels of climate change on multi-decadal scales, are sensitive to environmental variations associated with large-scale changes in climate, but that the effects will be determined by changes in environmental parameters regulating marine production and food availability on a local scale.
HMMoce : an R package for improved geolocation of archival-tagged fishes using a hidden Markov method

( 2017-11) Braun, Camrin D. ; Galuardi, Benjamin ; Thorrold, Simon R.

Electronic tagging of marine fishes is commonly achieved with archival tags that rely on light levels and sea surface temperatures to retrospectively estimate movements. However, methodological issues associated with light-level geolocation have constrained meaningful inference to species where it is possible to accurately estimate time of sunrise and sunset. Most studies have largely ignored the oceanographic profiles collected by the tag as a potential way to refine light-level geolocation estimates. Open-source oceanographic measurements and outputs from high-resolution models are increasingly available and accessible. Temperature and depth profiles recorded by electronic tags can be integrated with these empirical data and model outputs to construct likelihoods and improve geolocation estimates. The R package HMMoce leverages available tag and oceanographic data to improve position estimates derived from electronic tags using a hidden Markov approach. We illustrate the use of the model and test its performance using example blue and mako shark archival tag data. Model results were validated using independent, known tracks and compared to results from other geolocation approaches. HMMoce exhibited as much as 6-fold improvement in pointwise error as compared to traditional light-level geolocation approaches. The results demonstrated the general applicability of HMMoce to marine animals, particularly those that do not frequent surface waters during crepuscular periods.
Seascape and life-history traits do not predict self-recruitment in a coral reef fish

(The Royal Society, 2016-08-09) Herrera, Marcela ; Nanninga, Gerrit ; Planes, Serge ; Jones, Geoffrey P. ; Thorrold, Simon R. ; Saenz-Agudelo, Pablo ; Almany, Glenn R. ; Berumen, Michael L.

The persistence and resilience of many coral reef species are dependent on rates of connectivity among sub-populations. However, despite increasing research efforts, the spatial scale of larval dispersal remains unpredictable for most marine metapopulations. Here, we assess patterns of larval dispersal in the angelfish Centropyge bicolor in Kimbe Bay, Papua New Guinea, using parentage and sibling reconstruction analyses based on 23 microsatellite DNA loci. We found that, contrary to previous findings in this system, self-recruitment (SR) was virtually absent at both the reef (0.4–0.5% at 0.15 km2) and the lagoon scale (0.6–0.8% at approx. 700 km2). While approximately 25% of the collected juveniles were identified as potential siblings, the majority of sibling pairs were sampled from separate reefs. Integrating our findings with earlier research from the same system suggests that geographical setting and life-history traits alone are not suitable predictors of SR and that high levels of localized recruitment are not universal in coral reef fishes.
Erratum : Estimating westslope cutthroat trout (Oncorhynchus clarkii lewisi) movements in a river network using strontium isoscapes

(NRC Research Press, 2012-05-07) Muhlfeld, Clint C. ; Thorrold, Simon R. ; McMahon, Thomas E. ; Marotz, Brian
Markov Chain Monte Carlo methods for assigning larvae to natal sites using natural geochemical tags

(Ecological Society of America, 2008-12) White, J. Wilson ; Standish, Julie D. ; Thorrold, Simon R. ; Warner, Robert R.

Geochemical signatures deposited in otoliths are a potentially powerful means of identifying the origin and dispersal history of fish. However, current analytical methods for assigning natal origins of fish in mixed-stock analyses require knowledge of the number of potential sources and their characteristic geochemical signatures. Such baseline data are difficult or impossible to obtain for many species. A new approach to this problem can be found in iterative Markov Chain Monte Carlo (MCMC) algorithms that simultaneously estimate population parameters and assign individuals to groups. MCMC procedures only require an estimate of the number of source populations, and post hoc model selection based on the deviance information criterion can be used to infer the correct number of chemically distinct sources. We describe the basics of the MCMC approach and outline the specific decisions required when implementing the technique with otolith geochemical data. We also illustrate the use of the MCMC approach on simulated data and empirical geochemical signatures in otoliths from young-of-the-year and adult weakfish, Cynoscion regalis, from the U.S. Atlantic coast. While we describe how investigators can use MCMC to complement existing analytical tools for use with otolith geochemical data, the MCMC approach is suitable for any mixed-stock problem with a continuous, multivariate data.
Otolith geochemistry does not reflect dispersal history of clownfish larvae

( 2010-06) Berumen, Michael L. ; Walsh, Harvey J. ; Raventos, N. ; Planes, Serge ; Jones, Geoffrey P. ; Starczak, Victoria R. ; Thorrold, Simon R.

Natural geochemical signatures in calcified structures are commonly employed to retrospectively estimate dispersal pathways of larval fish and invertebrates. However, the accuracy of the approach is generally untested due to the absence of individuals with known dispersal histories. We used genetic parentage analysis (genotyping) to divide 110 new recruits of the orange clownfish, Amphiprion percula, from Kimbe Island, Papua New Guinea, into two groups: “self-recruiters” spawned by parents on Kimbe Island and “immigrants” that had dispersed from distant reefs (>10km away). Analysis of daily increments in sagittal otoliths found no significant difference in PLDs or otolith growth rates between self-recruiting and immigrant larvae. We also quantified otolith Sr/Ca and Ba/Ca ratios during the larval phase using laser ablation inductively coupled plasma mass spectrometry. Again, we found no significant differences in larval profiles of either element between self-recruits and immigrants. Our results highlight the need for caution when interpreting otolith dispersal histories based on natural geochemical tags in the absence of water chemistry data or known-origin larvae with which to test the discriminatory ability of natural tags.
Temperature and salinity effects on strontium incorporation in otoliths of larval spot (Leiostomus xanthurus)

(National Research Council Canada, 2004-02-03) Martin, Gretchen Bath ; Thorrold, Simon R. ; Jones, Cynthia M.

Temperature dependence of strontium/calcium (Sr/Ca) ratios in foraminiferal calcite and coral aragonite is well established; however, factors controlling Sr/Ca ratios in fish otoliths remain obscure. To assess temperature dependence of Sr/Ca in marine fish otoliths, we reared spot (Leiostomus xanthurus) larvae under controlled temperature (17–26 °C) and salinity (15‰ and 25‰). We found a significant linear relationship between temperature and Sr/Ca ratios, with a sensitivity of approximately 5%·°C–1. Otolith Sr/Ca values were also significantly higher at a salinity of 25‰ vs. 15‰, after accounting for differences in dissolved Sr/Ca ratios in the ambient water, with a sensitivity of approximately 1%/salinity (‰). These observations complicate the use of Sr/Ca ratios to determine temperature histories of spot larvae, because accurate temperature reconstructions are possible only with a priori knowledge of both ambient salinity and dissolved Sr/Ca ratios. Fully marine species residing in oceanic waters will not experience significant salinity variations; therefore, otolith Sr/Ca ratios may be useful recorders of temperature exposure. Otolith Sr/Ca thermometry in coastal fish species that make regular excursions into estuarine waters will be more problematic. Multiple geochemical tracers, including oxygen stable isotopes and other trace elements, may be necessary to accurately reconstruct temperature and salinity histories in these species.

Thorrold Simon R.

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