Validation of otolith δ18O values as effective natural tags for shelf-scale geolocation of migrating fish

The oxygen isotopic ratio of fish otoliths is increasingly used as a 'natural tag' to assess provenance in migratory species, with the assumption that variations in delta O-18 values closely reflect individual ambient experience of temperature and/or salinity. We employed archival tag data and otoliths collected from a shelf-scale study of the spatial dynamics of North Sea plaice Pleuronectes platessa L., to examine the limits of otolith delta O-18-based geolocation of fish during their annual migrations. Detailed intra-annual otolith delta O-18 measurements for 1997-1999 from individuals of 3 distinct sub-stocks with different spawning locations were compared with delta O-18 values predicted at the monthly, seasonal and annual scales, using predicted sub-stock specific temperatures and salinities over the same years. Spatio-temporal variation in expected delta O-18 values (-0.23 to 2.94%) mainly reflected variation in temperature, and among-zone discrimination potential using otolith delta O-18 varied greatly by temporal scale and by time of year. Measured otolith delta O-18 values (-0.71 to 3.09%) largely mirrored seasonally predicted values, but occasionally fell outside expected delta O-18 ranges. Where mismatches were observed, differences among sub-stocks were consistently greater than predicted, suggesting that in plaice, differential sub-stock growth rates and physiological effects during oxygen fractionation enhance geolocation potential using otolith delta O-18. Comparing intra-annual delta O-18 values over several consecutive years for individuals with contrasted migratory patterns corroborated a high degree of feeding and spawning site fidelity irrespective of the sub-stock. Informed interpretation of otolith delta O-18 values can therefore provide relatively detailed fisheries-relevant data not readily obtained by conventional means

The SEA-UNICORN European COST Action: Advancing Knowledge on Marine Connectivity to Support Transition to a Sustainable Blue Economy

The European COST Action “Unifying Approaches to Marine Connectivity for improved Resource Management for the Seas” (SEA-UNICORN, 2020‐2025) is an international research coordination initiative that unites an interdisciplinary community of scientists and policymakers from over 100 organizations across Europe and beyond. It is establishing a globally harmonized framework to deliver actionable, transdisciplinary knowledge of marine functional connectivity, promoting a sustainable blue economy and ocean conservation. Planning sustainable development in rapidly changing oceans requires a thorough comprehension of marine biodiversity and the processes underpinning the functioning of ecosystems. Connectivity among marine populations and habitats facilitates the persistence and resilience of vulnerable species and ecosystems and controls the spread of invasive species. Constructing effective networks of restoration or conservation areas and promoting sustainable harvesting requires knowledge of connectivity. SEA-UNICORN advances worldwide collaboration by coordinating the collection, sharing, and application of knowledge on species, community, and ecosystem connectivity at sea and at the land‐sea interface. It engages scientists from diverse areas and early-career researchers and creates a stronger match between natural and social science and policy needs to better address key environmental issues that challenge the future of our planet

The SEA-UNICORN European COST Action: Advancing Knowledge on Marine Connectivity to Support Transition to a Sustainable Blue Economy

Publication history: Published online 8 June 2022The European COST Action “Unifying Approaches to Marine Connectivity for improved Resource Management for the Seas” (SEA-UNICORN, 2020‐2025) is an international research coordination initiative that unites an interdisciplinary community of scientists and policymakers from over 100 organizations across Europe and beyond. It is establishing a globally harmonized framework to deliver actionable, transdisciplinary knowledge of marine functional connectivity, promoting a sustainable blue economy and ocean conservation. Planning sustainable development in rapidly changing oceans requires a thorough comprehension of marine biodiversity and the processes underpinning the functioning of ecosystems. Connectivity among marine populations and habitats facilitates the persistence and resilience of vulnerable species and ecosystems and controls the spread of invasive species. Constructing effective networks of restoration or conservation areas and promoting sustainable harvesting requires knowledge of connectivity. SEA-UNICORN advances worldwide collaboration by coordinating the collection, sharing, and application of knowledge on species, community, and ecosystem connectivity at sea and at the land‐sea interface. It engages scientists from diverse areas and early-career researchers and creates a stronger match between natural and social science and policy needs to better address key environmental issues that challenge the future of our planet.This publication is based upon work from COST Action CA19107 SEA-UNICORN, supported by COST (European Cooperation in Science and Technology, https://www.cost.eu/

Listening In on the Past: What Can Otolith δ18O Values Really Tell Us about the Environmental History of Fishes?

Oxygen isotope ratios from fish otoliths are used to discriminate marine stocks and reconstruct past climate, assuming that variations in otolith δ18O values closely reflect differences in temperature history of fish when accounting for salinity induced variability in water δ18O. To investigate this, we exploited the environmental and migratory data gathered from a decade using archival tags to study the behaviour of adult plaice (Pleuronectes platessa L.) in the North Sea. Based on the tag-derived monthly distributions of the fish and corresponding temperature and salinity estimates modelled across three consecutive years, we first predicted annual otolith δ18O values for three geographically discrete offshore sub-stocks, using three alternative plausible scenarios for otolith growth. Comparison of predicted vs. measured annual δ18O values demonstrated >96% correct prediction of sub-stock membership, irrespective of the otolith growth scenario. Pronounced inter-stock differences in δ18O values, notably in summer, provide a robust marker for reconstructing broad-scale plaice distribution in the North Sea. However, although largely congruent, measured and predicted annual δ18O values of did not fully match. Small, but consistent, offsets were also observed between individual high-resolution otolith δ18O values measured during tag recording time and corresponding δ18O predictions using concomitant tag-recorded temperatures and location-specific salinity estimates. The nature of the shifts differed among sub-stocks, suggesting specific vital effects linked to variation in physiological response to temperature. Therefore, although otolith δ18O in free-ranging fish largely reflects environmental temperature and salinity, we counsel prudence when interpreting otolith δ18O data for stock discrimination or temperature reconstruction until the mechanisms underpinning otolith δ18O signature acquisition, and associated variation, are clarified

Spatio-temporal Variation of Shallow Microhabitats and Associated Juvenile Fish Assemblages in a Mediterranean Lagoon

Coastal lagoons are known to host numerous resident and migrant fish species. Spatio-temporal variation in abiotic and biotic conditions in these ecosystems results, however, in a mosaic of microhabitats that could differently affect juvenile growth and survival. To deepen our understanding of juvenile fish habitat requirements and their spatio-temporal use of lagoons, microhabitat characteristics and fish assemblages were monitored jointly in a small temperate lagoon (the Prévost lagoon), from March to October 2019. A total of 2206 juvenile fishes belonging to 22 species were collected. Resident lagoon species, especially Atherina boyeri, dominated the assemblage (74%), while, among migrant species, Sparus aurata (8%) and Liza aurata (5%) were the most represented. Changes in overall juvenile abundance were mainly temporal, following the seasonal shifts in water temperature, salinity, and chlorophyll a concentration (44.9% of the co-inertia). However, our results revealed that distinct types of microhabitats exist in small lagoons and that juvenile fish distribution among them is non-random. Indeed, fish species richness mainly differed among sampling sites in relation to their distance from the inlet and the complexity of the three-dimensional habitat structure (36.5% of the co-inertia). Juveniles preferentially selected microhabitats with medium to high structural complexity, which were essentially created by macroalgae. However, microhabitat preferences were both species and ontogenetic stage dependent, with more contrasting microhabitat requirements in young juveniles. These results underline the need for conservation measures to consider each lagoon as a dynamic mosaic of microhabitats with radically different importance for the juveniles of the various fish species that colonize them

Oxygen and Temperature for Lagoons

Mean summer dissolved oxygen and water surface temperature values for the four major costal lagoons in the Gulf of Lions. Downloaded from www.ifremer.fr/surval2/ (n=57 data buoys)

Extensive larval dispersal and restricted movement of juveniles on the nursery grounds of sole in the Southern North Sea

Connectivity between spawning and nursery grounds influences the colonization, replenishment and resilience of populations of marine organisms. Connectivity rate, measured as the exchange of individuals between spawning and nursery grounds, is therefore a crucial determinant of stock size. However, connectivity of early-life stages is hard to explore due to sampling limitations and insufficient knowledge on potential larval sources. Here we present new insights into pre- and post-settlement dispersal of the common sole (Solea solea L.) at a spatial scale of 5–500 km in the Southern North Sea. Patterns at a scale of <100 km were considered local, whereas patterns further than 100 km were considered regional. Multi-elemental signatures of the otolith edge of 213 juvenile sole were used to discriminate at 79% of overall accuracy three main nursery grounds in the Southern North Sea, namely UK coast, Belgian coast and Dutch Wadden Sea. Interregional differences in otolith composition (especially for Mg, Mn and Ba) suggest that sole migration following settlement is limited in the Southern North Sea. Elemental signatures of the same fish indicated mixing during larval dispersal. Each nursery ground recruited an important mix of juveniles from three of the four chemically distinct natal sources identified from the larval otolith signatures. However the percentage of correct regional re-assignment varied from 67 to 80% with a maximum in the Wadden Sea. The results contributed to the validation of biophysical models of larval drift. Our findings support decision making for both fisheries management and marine spatial planning at the national and European level

Modeling larval dispersal for the gilthead seabream in the northwestern Mediterranean sea

To investigate dispersal and connectivity between spawning and lagoon nursery habitats of the gilthead seabream, Sparus aurata, in the Gulf of Lions (northwestern Mediterranean Sea), we modeled the potential transport of the species’ larvae between its supposed main spawning site in the region (the Planier Island) and two of its main local nursery areas (the coastal lagoons of Thau and Salses-Leucate). Passive larval drift simulations using a dispersal biophysical model showed a large variability in the possible trajectories from spawning to nursery areas and in the predicted ages for larvae arrival on the two nursery sites. The most common ages at arrival obtained in the simulations (20–60 days) are broadly consistent with previous modeling studies but contrast with the actual ages of the S. aurata post-larvae collected in 2016 and 2017 at time of the lagoon entrances (60–90 days, from otolith readings). The period between 25 and 70 days being critical for gilthead seabream larvae to acquire sufficient swimming, osmoregulatory, and olfactory abilities to enter coastal lagoons, we argue that ontogenic development plays a crucial role in the transport and local retention of S. aurata larvae in the studied region, explaining the discrepancy between simulation results and observed data

Allometry Data

Sparus aurata otolith radius (rad4) and fish length or weight, to be used in an allometry model

Growth Data

Growth and temperature data to be used in the integral projection model