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.
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.
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.
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.
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.
Biophysical mechanisms of larval fish ingress into Chesapeake Bay

(Inter-Research, 2005-11-21) Hare, Jonathan A. ; Thorrold, Simon R. ; Walsh, Harvey J. ; Reiss, Christian S. ; Valle-Levinson, Arnoldo ; Jones, Cynthia M.

Selective tidal stream transport is hypothesized as a dominant mechanism by which larvae of marine animals move through estuarine openings. For larvae moving from the shelf to estuarine habitats, selective tidal stream transport proposes that larvae are higher in the water column during flood tide and lower in the water column during ebb tide. Although a number of studies conclude that selective tidal stream transport is the mechanism responsible for larval ingress, few studies consider alternative mechanisms or consider passive explanations for tidal patterns in larval distributions. We examined the biophysical mechanisms responsible for larval ingress into Chesapeake Bay using an Eulerian approach. We made flux calculations for 3 species and partitioned flux estimates among 3 different ingress mechanisms (wind forcing, residual bottom inflow and tidal). For the Atlantic croaker Micropogonias undulatus (Sciaenidae), all 3 mechanisms of ingress contributed to the net up-estuary flux of larvae, but tidal mechanisms become more important for larger sizes. Net up-estuary flux of the Atlantic menhaden Brevoortia tyrannus (Clupeidae) was dominated by residual bottom inflow and wind forcing. Ingress of the summer flounder Paralichthys dentatus (Paralichthyidae) was dominated by tidal mechanisms, and the importance of tides increased with developmental stage. We found little evidence for the hypothesis that tidal patterns in larval distributions resulted from passive processes (water mass-specific distributions, buoyancy, vertical mixing), thereby supporting the hypothesis that tidal patterns resulted from active behaviors. However, our estimates of vertical mixing were not direct and additional work is needed to examine the role of vertical mixing in influencing vertical distributions in areas with strong tides. We conclude that a combination of wind forcing, residual bottom inflow, and selective tidal stream transport are responsible for the ingress of larval fishes into Chesapeake Bay, and that the relative importance of the 3 mechanisms differs among species and changes with larval development.
Temperature and salinity effects on magnesium, manganese, and barium incorporation in otoliths of larval and early juvenile spot Leiostomus xanthurus

(Inter-Research, 2005-06-02) Martin, Gretchen Bath ; Thorrold, Simon R.

The use of otolith chemistry to delineate fish populations and trace migration pathways is premised on a significant correlation between the elemental composition of otoliths and physicochemical properties of the ambient environment. However, few experiments have been rigorously designed to address the effects of temperature and salinity on the elemental composition of otoliths. We examined the effects of temperature and salinity on the incorporation of magnesium (Mg), manganese (Mn), and barium (Ba) in the otoliths of larval and early juvenile spot Leiostomus xanthurus by rearing fish in the laboratory under controlled environmental conditions. L. xanthurus are an estuarine dependent species that traverse varying temperature and salinity regimes throughout their life histories. It is important, therefore, to understand the influence of physicochemical properties of different water masses before attempting to reconstruct important life history transitions based on variations in otolith chemistry. Both [Mg/Ca]otolith and the Mg partition coefficient, DMg, were not significantly affected by either temperature or salinity, but were correlated with otolith precipitation and somatic growth rates. Temperature and salinity had significant interaction effects on DMn, but not on [Mn/Ca]otolith. Finally, DBa was influenced by salinity but not temperature. These results highlight the complex nature of elemental deposition in otoliths, and suggest that both environmental and physiological effects likely influence elemental ratios in fish otoliths.
Recovery of temperature records from slow-growing corals by fine scale sampling of skeletons

(American Geophysical Union, 2007-09-12) Cohen, Anne L. ; Thorrold, Simon R.

We used laser ablation inductively coupled plasma mass spectrometry (LA ICP-MS) to analyze Sr/Ca ratios in 5 colonies of the Atlantic corals, Diploria labyrinthiformis and Montastrea franski, each growing less than 5 mm yr−1. By targeting the centers of septa we avoided thickening deposits to achieve an analytical sampling resolution of 5-10 days. The sensitivity of Sr/Ca to temperature (−0.096 mmol/mol/°C) is ∼3 times higher than previously reported for these species and equivalent to that exhibited by fast-growing Porites corals from the Indo-Pacific. The Sr/Ca-sea surface temperature (SST) calibrations derived from these corals were not statistically different and were independent of colony growth rate over the period studied. Data from 4 D. labyrinthiformis colonies were pooled to produce a single Sr/Ca-SST calibration with a calculated standard error on the predicted ocean temperature of ±0.51°C. Applying our calibration to Sr/Ca analyses of D. labyrinthiformis skeleton deposited in the late 18th century indicated that average annual sea surface temperatures around Bermuda were ∼1°C cooler than today.
Temperature and salinity effects on elemental uptake in the shells of larval and juvenile softshell clams Mya arenaria

(Inter-Research, 2008-10-28) Strasser, Carly A. ; Mullineaux, Lauren S. ; Thorrold, Simon R.

The chemical composition of biogenic carbonate has great potential to serve as a natural tag in studies of marine population connectivity. Yet the degree to which carbonate chemistry reflects ambient water composition may be influenced by environmental parameters, physiology, and uptake kinetics. We explored the effects of temperature and salinity on the uptake of elements into shells of larval and juvenile softshell clams Mya arenaria. Clams were reared under controlled conditions using combinations of temperatures (15, 20, and 24°C) and salinities (22 and 30‰) commonly encountered in their natural habitat. We analyzed the ratios of a suite of elements (Mg, Mn, Sr, Ba and Pb) to Ca in seawater and shells using solution-based inductively coupled plasma-mass spectrometry (ICP-MS). Elemental ratios were translated into discrimination coefficients (Delement) to account for water chemistry variability among treatments. For larval shell, we found that DMn was lower in the low-temperature treatment than at higher temperatures, had mixed results for correlations with salinity, and exhibited an interactive effect between salinity and temperature. We also found that DBa of larval shell was higher in the 15°C treatment than at the other 2 temperatures. In juvenile shell, we found a temperature effect for DMn, however the exact relationship was unclear because DMn was higher in the mid-temperature treatment than either the low- or high-temperature treatments. DSr was negatively correlated with salinity in juveniles, with evidence of an interactive effect for temperature and salinity. DBa and DPb were both higher in juveniles in the low-temperature treatment than in the 2 higher temperatures. When discrimination coefficients significantly differed based on ANOVA, we used post hoc comparisons to further explore the effects of temperature and salinity. Correlation analyses showed that uptake differed significantly between larval and juvenile M. arenaria shell for all elements, with no predictable relationship in shell uptake between the 2 stages except for DBa. All of the elements examined in this study have the potential to be useful in tagging studies where geographic variability in temperature, salinity or elemental concentrations exists, although caution should be used to ensure any biological interactions with these variables are accounted for in data interpretation.
Salinity change in the subtropical Atlantic : secular increase and teleconnections to the North Atlantic Oscillation

(American Geophysical Union, 2005-01-21) Rosenheim, Brad E. ; Swart, Peter K. ; Thorrold, Simon R. ; Eisenhauer, Anton ; Willenz, Philippe

Recent studies comparing shipboard data between the 1950's and the 1990's have shown significant, heterogeneous adjustments of the temperature-salinity structure of the N. Atlantic Ocean. Here, we present proxy records of temperature and salinity from aragonite sclerosponge skeletons, extending existing records of the Salinity Maximum Waters (SMW) of the N. Atlantic back to 1890. These proxy records show secular temperature increases of 1.6–2.0°C, higher than published global averages, and salinity increases of 0.35–0.5 psu, smaller than short-term secular trends recently measured. Salinity reconstructions vary more significantly on the decadal scale, showing changes that are related to low-frequency variations of the North Atlantic Oscillation (NAO). On both secular and decadal time scales, the records indicate significant thermohaline changes in the SMW, either via forcing at the surface or increasing depths of density surfaces in the Bahamas.
Estimating connectivity in marine populations : an empirical evaluation of assignment tests and parentage analysis under different gene flow scenarios

( 2008-11-21) Saenz-Agudelo, Pablo ; Jones, Geoffrey P. ; Thorrold, Simon R. ; Planes, Serge

The application of spatially explicit models of population dynamics to fisheries management and the design marine reserves network systems has been limited due to a lack of empirical estimates of larval dispersal. Here we compared assignment tests and parentage analysis for examining larval retention and connectivity under two different gene flow scenarios using panda clownfish (Amphiprion polymnus) in Papua New Guinea. A metapopulation of panda clownfish in Bootless Bay with little or no genetic differentiation among 5 spatially discrete locations separated by 2-6km provided the high gene flow scenario. The low gene flow scenario compared the Bootless Bay metapopulation with a genetically distinct population (Fst = 0.1) located at Schumann Island, New Britain, 1,500km to the north-east. We used assignment tests and parentage analysis based on microsatellite DNA data to identify natal origins of 177 juveniles in Bootless Bay and 73 juveniles at Schumann Island. At low rates of gene flow, assignment tests correctly classified juveniles to their source population. On the other hand, parentage analysis led to an overestimate of self-recruitment within the two populations due to the significant deviation from panmixia when both populations were pooled. At high gene flow (within Bootless Bay), assignment tests underestimated self-recruitment and connectivity among subpopulations, and grossly overestimated self-recruitment within the overall metapopulation. However, the assignment tests did identify immigrants from distant (genetically distinct) populations. Parentage analysis clearly provided the most accurate estimates of connectivity in situations of high gene flow.
Continental-scale variation in otolith geochemistry of juvenile American shad (Alosa sapidissima)

(NRC Research Press, 2008-11-26) Walther, Benjamin D. ; Thorrold, Simon R.

We assembled a comprehensive atlas of geochemical signatures in juvenile American shad (Alosa sapidissima) to discriminate natal river origins on a large spatial scale and at a high spatial resolution. Otoliths and (or) water samples were collected from 20 major spawning rivers from Florida to Quebec and were analyzed for elemental (Mg:Ca, Mn:Ca, Sr:Ca, and Ba:Ca) and isotope (87Sr:86Sr and δ18O) ratios. We examined correlations between water chemistry and otolith composition for five rivers where both were sampled. While Sr:Ca, Ba:Ca, 87Sr:86Sr, and δ18O values in otoliths reflected those ratios in ambient waters, Mg:Ca and Mn:Ca ratios in otoliths varied independently of water chemistry. Geochemical signatures were highly distinct among rivers, with an average classification accuracy of 93% using only those variables where otolith values were accurately predicted from water chemistry data. The study represents the largest assembled database of otolith signatures from the entire native range of a species, encompassing approximately 2700 km of coastline and 19 degrees of latitude and including all major extant spawning populations. This database will allow reliable estimates of natal origins of migrating ocean-phase American shad from the 2004 annual cohort in the future.
Limited diversity in natal origins of immature anadromous fish during ocean residency

( 2009-10) Walther, Benjamin D. ; Thorrold, Simon R.

Variable migration patterns can play a significant role in promoting diverse life history traits among populations. However, population and stage specific movement patterns are generally unknown yet crucial aspects of life history strategies in many highly migratory species. We used a natural tag approach using geochemical signatures in otoliths to identify natal origins of one-year-old anadromous American shad (Alosa sapidissima) during ocean residency. Otolith signatures of migrants were compared to a database of baseline signatures from 20 source populations throughout their spawning range. Samples were dominated by fish from only two rivers, while all other potential source populations were nearly or completely absent. These data support the hypothesis that American shad exhibit diverse migratory behaviors and immature individuals from populations throughout the native range do not all mix on northern summer feeding grounds. Rather, our results suggest populations of anadromous fish are distributed heterogeneously at sea in the first year of life and thus may encounter different ocean conditions at a critical early life history stage.
Inter-annual variability in isotope and elemental ratios recorded in otoliths of an anadromous fish

( 2008-10) Walther, Benjamin D. ; Thorrold, Simon R.

Isotope ratios and elemental concentrations in otoliths are often used as natural tags to reconstruct migratory movements and connectivity patterns in marine and anadromous fishes. Although differences in otolith geochemistry have been documented among geographically separated populations, inter-annual variation within locations is less frequently examined. We compared otolith isotope (δ18O and 87Sr:86Sr) and elemental ratios (Sr:Ca and Ba:Ca) from several annual cohorts of juvenile American shad (Alosa sapidissima) in three rivers. These four geochemical signatures distinguished among river-specific populations of this species at both large and small geographic scales, with δ18O and 87Sr:86Sr generating the majority of multivariate variation. We found significant variation among years for all variables in two to three rivers. However, the magnitude of variability differed among ratios, with δ18O ratios showing substantial inter-annual shifts while 87Sr:86Sr ratios were relatively stable across years. Sr:Ca and Ba:Ca ratios also varied among years. These results imply that investigators using environmentally labile signatures must quantify geochemical signatures for each cohort of interest in order to confidently identify origins of migrants.
Geochemical signatures in otoliths record natal origins of American shad

(American Fisheries Society, 2008-01-03) Walther, Benjamin D. ; Thorrold, Simon R. ; Olney, John E.

Population connectivity is a critical component in the life history dynamics of anadromous fishes and in the persistence of local populations. We used geochemical signatures in the otoliths of American shad Alosa sapidissima to determine natal origins and estimate rates of straying among river-specific populations along the U.S. Atlantic coast. Stable isotope (δ13C, δ18O and 87Sr:86Sr) and elemental (Mg:Ca, Mn:Ca, Sr:Ca and Ba:Ca) signatures in otoliths of juvenile American shad from rivers from Georgia to New Hampshire varied significantly, allowing for an average of 91% cross-validated accuracy when classifying individual fish to their natal rivers. We also found significant interannual variability in the geochemical signatures from several rivers, due largely to differences in δ18O values among years. We then used the ground-truthed geochemical signatures in the otoliths of juvenile American shad to identify the natal origins of spawning adults in the York River system in Virginia. Approximately 6% of the spawning adults collected in the York River were strays from other rivers. Of the remaining fish, 79% were spawned in the Mattaponi River and 21% in the Pamunkey River. The combined results of this and other recent studies suggest that although most American shad spawning in the York River were homing to their natal river, there was much less fidelity to individual tributaries. Small-scale straying could allow fish spawned in the Mattaponi River to subsidize spawning in the Pamunkey River, which has experienced persistent recruitment failure
Population connectivity in marine systems : an overview

(Oceanography Society, 2007-09) Cowen, Robert K. ; Gawarkiewicz, Glen G. ; Pineda, Jesus ; Thorrold, Simon R. ; Werner, Francisco E.

There is growing consensus that life within the world’s ocean is under considerable and increasing stress from human activities (Hutchings, 2000; Jackson et al., 2001). This unprecedented strain on both the structure and function of marine ecosystems has led to calls for new management approaches to counter anthropogenic impacts in the coastal ocean (Botsford et al., 1997; Browman and Stergiou, 2004: Pikitch et al., 2004). Spatial management, including Marine Protected Areas (MPAs), has been touted as a method for both conserving biodiversity and managing fisheries (Agardy, 1997). Continuing debates on the efficacy of MPAs have identified the need for models that capture the spatial dynamics of marine populations, especially with respect to larval dispersal (Willis et al., 2003; Sale et al., 2005). Theoretical studies suggest that population connectivity plays a fundamental role in local and metapopulation dynamics, community dynamics and structure, genetic diversity, and the resiliency of populations to human exploitation (Hastings and Harrison, 1994; Botsford et al., 2001). Modeling efforts have been hindered, however, by the paucity of empirical estimates of, and knowledge of the processes controlling, population connectivity in ocean ecosystems. While progress has been made with older life stages, the larval-dispersal component of connectivity remains unresolved for most marine populations. This lack of knowledge represents a fundamental obstacle to obtaining a comprehensive understanding of the population dynamics of marine organisms. Furthermore, a lack of spatial context that such information would provide has limited the ability of ecologists to evaluate the design and potential benefits of novel conservation and resource-management strategies.
Water, not food, contributes the majority of strontium and barium deposited in the otoliths of a marine fish

(Inter-Research, 2006-04-13) Walther, Benjamin D. ; Thorrold, Simon R.

We quantified the relative contributions of water and food to strontium (Sr) and barium (Ba) deposited in otoliths of juvenile mummichogs Fundulus heteroclitus. Fish were reared in seawater spiked with 86Sr and 137Ba significantly beyond natural values to obtain distinct isotopic signatures for water and food. Element abundances (Sr:Ca and Ba:Ca) and isotope ratios (88Sr:86Sr and 138Ba:137Ba) were quantified in water samples using solution-based inductively coupled plasma-mass spectrometry (ICP-MS), and 88Sr:86Sr and 138Ba:137Ba ratios in otoliths were quantified using laser ablation ICP-MS. The relative contributions of water and food sources to otolith aragonite were assessed using a simple linear isotope mixing model. Water sources contributed 83% of Sr and 98% of Ba in otoliths formed in spiked seawater. Our results indicate that water chemistry is the dominant factor controlling the uptake of Sr and Ba in the otoliths of marine fishes. Thus, chemical signatures recorded in the otoliths of marine fishes should reflect the ambient water composition of these elements at the time of deposition.
Population connectivity and larval dispersal : using geochemical signatures in calcified structures

(Oceanography Society, 2007-09) Thorrold, Simon R. ; Zacherl, Danielle C. ; Levin, Lisa A.

The importance of larval dispersal to the population dynamics and biogeography of marine organisms has been recognized for almost a century (Hjort, 1914; Thorson, 1950). More recently, theoretical studies have highlighted the role that connectivity may play in determining the resilience of marine populations (Hastings and Botsford, 2006). Effective spatial management of marine capture fisheries, including the design of marine reserve networks, also requires an understanding of population connectivity (Sale et al., 2005). However, remarkably few empirical estimates of larval dispersal or population connectivity in ocean environments exist.
Spatial and temporal variation in elemental signatures of statoliths from the Patagonian longfin squid (Loligo gahi)

(National Research Council Canada, 2004-09-09) Arkhipkin, Alexander I. ; Campana, Steven E. ; FitzGerald, Jennifer L. ; Thorrold, Simon R.

We quantified elemental signatures in statoliths of 718 Patagonian longfin squid (Loligo gahi) collected in the vicinity of the Falkland Islands (southwest Atlantic) and at sites on the Patagonian Shelf and coastal Peru. All squid were assigned to a spawning cohort by size, spawning condition, and back-calculated spawning date based on daily increments in statoliths. The remaining statolith was then analyzed for six elemental ratios (Mg/Ca, Mn/Ca, Sr/Ca, Cd/Ca, Ba/Ca, and Pb/Ca) using high-resolution inductively coupled plasma mass spectrometry (ICP-MS). Elemental concentrations in the statoliths were broadly similar to other biogenic aragonites. Differences in Sr/Ca ratios in statoliths among geographic locations were generally consistent with a negative correlation between Sr/Ca and temperature. Variations in statolith Cd/Ca and Ba/Ca values confirmed that during winter months, the squid were foraging deeper in the water column. Both Mg/Ca and Mn/Ca ratios in statoliths decreased with squid size, probably corresponding to a decrease in the contribution of the organic component of the statolith. Elemental signatures in the statoliths of L. gahi varied significantly geographically and between spring- and autumn-spawned cohorts, which must therefore have spent significant portions of their life histories in different environments.

Thorrold Simon R.

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