Indicios preliminares de variaciones ontogenéticas y espaciales en las señales isotópicas y elementales de otolitos de Solea solea del Golfo de León (Mediterráneo noroccidental)

Knowledge of fish life cycles is important for exploited species. In the Mediterranean Sea, catches of common sole (Solea solea) have fluctuated widely since the 1970s. Solea solea displays an ontogenetic shift in habitat: sole larvae are marine, juveniles inhabit shallow marine waters and coastal lagoons and adults inhabit deeper marine waters. Although the results of this study were obtained using only a small set of individuals, the otolith elemental composition and isotopic ratios were investigated for the three life stages (post-larval, juvenile and adult) in order to acquire a better knowledge of the variability in environmental conditions experienced by the common sole at each life stage in the NW Mediterranean. Moreover, this study provides the first evaluation of the potential of whole otolith microchemistry for investigating habitat connectivity in sole populations from the Gulf of Lions. The elemental and isotopic signatures of otoliths of post-larvae captured in various environments appear to show variations related to the River Rhône inputs (high Ba/Ca and low Sr/Ca ratios). Juveniles appear to show significant variations in otolith elemental and isotopic compositions depending not only on the physico-chemical properties of water in the nurseries they inhabit (Rhône River, Thau or Mauguio lagoons), but also as a result of variations in the chemical composition of their surrounding sediments and in their benthic prey. Adults exhibit otolith differences for isotopic ratios only, which is probably linked to the River Rhône inputs. Finally, several significant relationships were observed between otolith elemental composition and fish size in specimens captured at the River Rhône mouth. However, these variations seem to be an indication of the composition acquired in each environment rather than a sign of ontogeny.El conocimiento del ciclo de vida es importante para las especies comerciales de peces. En el mar Mediterráneo, las capturas de lenguado común (Solea solea) han fluctuado ampliamente desde la década de los 70. Solea solea presenta un cambio de hábitat ontogenético, las larvas son marinas, los juveniles viven en aguas marinas y en lagunas costeras, y los adultos viven en aguas marinas más profundas. Aunque los resultados de este estudio fueron obtenidos usando sólo un número pequeño de individuos, la composición de elemental los otolitos y las relaciones isotópicas fueron investigados en las tres etapas de vida (post-larval, juveniles y adultos) con el fin de adquirir un mejor conocimiento de la variabilidad en las condiciones ambientales que experimenta el lenguado común en cada etapa de la vida en el mediterráneo noroccidental. Por otra parte, este trabajo permite una primera evaluación del potencial de toda la microquímica de otolitos para la investigación de la conectividad del hábitat en las poblaciones de lenguado en el Golfo de León. Las señales elementales e isotópicos de los otolitos de las post-larvas capturadas en diferentes entornos muestran variaciones en relación a los materiales aportados por del río Ródano (alta relación Ba/Ca y baja relación Sr/Ca). Los juveniles parecen mostrar variaciones significativas en la composición elemental e isotópica de los otolitos dependiendo no sólo de las propiedades físico-químicas del agua en los viveros que habitan (Thau, Mauguio o el río Ródano), sino también como resultado de las variaciones en la composición química de los sedimentos circundantes y de su presa béntica. Los adultos presentan únicamente diferencias en las relaciones isotópicas de los otolitos, que está probablemente vinculado a por materiales aportados por el río Ródano. Por último, se observaron varias relaciones significativas entre la composición elemental de los otolitos y el tamaño de los peces en las muestras capturadas en la desembocadura del río Ródano. Sin embargo, estas variaciones parecen ser una indicación de la composición adquirida en cada entorno, más que ser debidas a la ontogenia

Analyse de la dispersion larvaire des poissons récifaux à la Réunion à travers l'étude de leurs otolithes

L'objectif principal de cette étude est d'apporter des informations sur la phase dispersive des larves des poissons récifaux à La Réunion, sujet fondamental afin d'appréhender les connectivités possibles entre les îles d'une même région. Les secrets de cette phase dispersive peu connue seront recherchés via l'étude des otolithes des poissons. Les propriétés particulières des otolithes confèrent des applications qui seront utilisées dans le cadre de ce travail : discriminateur de stocks via des analyses de forme (analyse de Fourier), horloge chronologique via la lecture des stries de croissance, et marqueur environnemental via des analyses microchimiques (éléments-traces, isotopes). Quatre espèces ichtyologiques d'intérêt commercial ont été choisies : Epinephleus merra (Serranidae), Mulloidichthys flavolineatus (Mullidae), Gnathodentex aurolineatus (Lethrinidae) et Lutjanus kasmira (Lutjanidae). Les paramètres de la vie larvaire des espèces étudiées dans ce travail leur confèrent la capacité d'établir des connectivités entre La Réunion et d'autres îles de l'Océan Indien (Maurice, Rodrigues, Madagascar). Néanmoins, dans un contexte hydrodynamique normal, et en associant d'autres facteurs (isolement géographique de l'île, faible flux larvaire, effet d'île sur la côte ouest, croissances larvaires élevées), l'hypothèse d'un auto-recrutement est favorisée. Ces résultats sont à prendre en compte dans la gestion durable de ces populations ichtyques vulnérables, à La RéunionThis objective of the present study, is to give informations about the oceanic larval phase of the coral reef fishes in Reunion Island. This knowledge is fundamental in grasping the potential interrelationships between islands of the same region applied to the reef fish of Reunion Island. The secrets of this little-known dispersive phase are explored through the study of fish otoliths. The particular properties of otoliths enable the various applications that have been used in the framework of this study: as discriminators of stocks via analysis of form (Fourier analysis), as chronological clocks via microchemical analysis (trace elements, isotopes). Four ichtyological and commercial species were chosen: Epinephelus merra (Serranidae), Mulloidichthys flavolineatus (Mullidae), Gnathodentex aurolineatus (Lethrinidae) and Lutjanus kasmira (Lutjanidae). In this study, the larval parameters of these species endows them with the capacity of establishing interconnections between Reunion Island and others islands in the Indian Ocean (Mauritius, Rodrigues, Madagascar). Nevertheless, given a normal hydrodynamic context, and in associating others factors (geographic isolation of Reunion, weak larval flux, effect of the island's in the west coast, elevated larval growth), the hypothesis of auto-recruitment is favored. These results should be taken into account in the management of the halieutic vulnerable resources of the coral reefs of Reunion IslandSAINT DENIS/REUNION-Droit Lettre (974112101) / SudocBANYULS/MER-Observ.Océanol. (660162201) / SudocPARIS-Museum-Bib. d'ichtyologie (751052306) / SudocPARIS-Museum Hist.Naturelle (751052304) / SudocSudocFranceReunionFRR

Characterisation of local populations of the common sole Solea solea (Pisces, Soleidae) in the NW Mediterranean through otolith morphometrics and shape analysis

Shape analyses were carried out on otoliths of the common sole, Solea solea (Linnaeus, 1758), in order to discriminate local populations in the North- Western Mediterranean Sea. Samples were collected in various environments like coastal lagoons, the outlet of the Rhone River as well as other marine sites. Morphological analyses highlighted a significant asymmetry between the left and right otoliths. This character could be acquired during or shortly after settlement on softbottoms when the individuals really become flatfishes. The otolith shape was described by seven harmonics from elliptic Fourier descriptors and by five indices of shape (coefficient of form, roundness, circularity, rectangularity, and ellipticity). The existence of several local populations of common sole in the NW Mediterranean was demonstrated. In particular, discriminant analyses highlighted significant differences in otolith shape according both to fish size and to the types of environment in which the fish live, i.e. coastal lagoons vs. marine sites, but also between sites belonging to the same type (lagoons, and marine sites). The differences in shape could be linked (1) to the particular environmental conditions of each site, and (2) to changes in metabolic and/or physiological conditions according to the stage of development of the fish which most likely influences the otolith growt

From the geochemistry of coral reef fish otoliths to climate : what can we learn from the example ofTaiaro lagoon ?

International audienceThe analysis of the C-O stable isotope composition of coral reef fish otoliths from Taiaro, a French Polynesian atoll normally isolated from the Pacific Ocean, has been performed to address two main questions. The first is to confirm previous results which suggest that a lagoonal coral reef fish population is able to achieve its ontogenetic cycle without any open ocean phase. If so, are O isotopic values of otoliths an indicator of temperature fluctuations in the tropical Pacific Ocean related to climate change and in particular temperature variations of water masses? δ18O and δ13C values on both lagoon and open ocean fish otoliths caught in 2006 indicated clearly that O-isotopes reached the isotopic equilibrium; in contrast, all δ13C values exhibited a strong isotopic disequilibrium related to metabolic activity. Stable isotope compositions revealed a clear differentiation between fish from lagoons and those from the open ocean (with a δ18O enrichment of 1 ‰ in favour of the lagoon). This confirmed a lack of connectivity between habitats and that fish from lagoon lived their entire life cycle in the lagoon. Both δ18O and δ13C data indicated differences between nucleus and edge signatures with changes in fish behavior from the larval life to adulthood (habitat, diet, etc.), and a clear adaptation of dietary behavior of lagoon fish. The comparison of the 2006 data set with those of 1994 showed that environmental conditions were stable in the lagoon, leading to a very narrow range of variations in the δ18O values. δ18O of fish otoliths of the open ocean exhibited a wider variation (+0.25 ‰) between 1994 and 2006, suggesting a decrease in temperature linked to a change of SST, which can be interpreted in terms of climate change associated with El Nino Southern Oscilation (ENENSO). These differences could also be due to a switch of habitats during the life cycle of fish from the open ocean

Composition isotopique δ18O-δ13C des otolithes des populations de poissons récifaux de Taiaro (Tuamotu, Polynésie française) : implications isotopiques et biologiques

International audienceNuclei (larval stage) and outer parts (adult stage) of fish otoliths from the Taiaro closed lagoon (French Polynesia) and adjacent ocean have been analysed for the C–O isotopic compositions. δ18O values of the nuclei of both populations indicate that isotopic equilibrium is reached. This impliesthat the lagoonal fish population has done its complete biological cycle in the lagoon and represents an adaptation ina closed system. δ18O values of the outer parts show a slight isotopic disequilibrium (< 0.2‰) interpreted in term of vital effect. All the δ13C values exhibit a strong isotopic disequilibrium related to metabolic activityLes compositions isotopiques (O–C) des nucleus (stade larvaire) et des zones périphériques (stade adulte) d’otolithes de poissons du lagon fermé de Taiaro (Polynésie française) et de l’océan Pacifique adjacent ont été mesurées. Les valeurs de δ18O des nucleus des deux populations indiquent que l’équilibre isotopique est atteint. Par conséquent, la population de poissons du lagon a effectué son cycle biologique complet dans le lagon et représente une adaptation au milieu fermé. Les valeurs de δ18O des parties périphériques respectives montrent un léger déséquilibre (< 0,2 ‰), interprété comme un effet vital. Les valeurs de δ13C montrent un profond déséquilibre isotopique associé au métabolism

Oceanic larval life of La Réunion ‘bichiques', amphidromous gobiid post-larvae

International audienceThe 2 amphidromous gobiids Sicyopterus lagocephalus and Cotylopus acutipinnis from La Réunion Island (Mascarene archipelago, south-western Indian Ocean) are heavily exploited by traditional fisheries during their river colonisation. Traits of their oceanic larval life were investigated to better understand the complex life cycle of these fishes. Age estimates were established using otolith increment counts and an alizarin complexon validation method. Larval duration was longer for the widespread S. lagocephalus (133 to 266 d; mean 199 ± 33 d) than for the endemic C. acutipinnis (78 to 150 d; mean 101 ± 14 d), which reflects their distributional ranges. For both species, no correlation was established between age and size, suggesting a decrease in growth during the larval phase. From the back-calculated birth dates, all S. lagocephalus of a major colonisation episode (December 2002) were hatched during the cool season. All results are discussed in terms of the recruitment origins of S. lagocephalus and C. acutipinnis within the Mascarenes. Recognition of the differences in larval life traits is essential for proposing both management and conservation measures for each species

Development of a key using morphological characters to distinguish south-western Indian Ocean anguillid glass eels

International audienceTwo morphological characters were examined in 4099 anguillid glass eels sampled in four south-western Indian Ocean islands, and resulting identifications were tested using genetic analysis. Distance between the origin of the dorsal and anal fins as related to total length and tail and caudal fin pigmentation enabled formulation of a useful field identification key, which was able to discriminate 4036 glass eels of the regional species Anguilla bicolor bicolor, Anguilla marmorata and Anguilla mossambica, and excluded the occurrence of Anguilla nebulosa labiata in the sample

Are elemental and strontium isotopic microchemistry of otolith and histomorphometrical characteristics of vertebral bone useful to resolve the eel angilla obscura status in Lalolalo lake in Wallis Island ?

International audienceOtolith Sr/Ca, Ba/Ca and 87 Sr/ 86 Sr ratios and vertebral bone histomorphometry were used to investigate the life-history of Anguilla obscura eels from an enclosed lake, Lalolalo (Wallis Island in the Pacific), with no apparent connection with the sea. 87 Sr/ 86 Sr isotopic ratio from the core region gives evidence of indisputable marine origin of eels caught in the lake suggesting that underground connections between the lake and the sea exist. Sr/Ca and Ba/Ca ratios recorded after the elver mark are undifferentiated from seawater ones, thus limiting their used as marker of entrance in the lake and movement. However, 87 Sr/ 86 Sr isotopic ratio demonstrated that: 1) eels enter in the lake just after their metamorphosis and spend their entire adult life in the lake and 2) the lake chemistry is consistent with 1 % seawater-like contribution and 99 % basalt weathering and/or geothermal spring contribution. The vertebrae do not show a particular demineralization of bone matrix (45-52 %). Reversely, the study of bone compactness shows an important loss of bone that favors the hypothesis of a genital maturation that arises in the ecological state of the lake