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Stocking is often used to supplement wild populations that are overexploited or have collapsed, yet it is unclear how this affects the genetic diversity of marine invertebrate populations. During the 1970s, a lobster stock enhancement program was carried out around the island of Corsica in the Mediterranean using individuals translocated from the Atlantic coast of France. This included the release of thousands of hatchery‐reared postlarval lobsters and several adult individuals, but no monitoring plan was established to assess whether these animals survived and recruited to the population. In this study, we sampled European lobster (Homarus gammarus) individuals caught around Corsica and tested whether they showed Atlantic ancestry. Due to a natural marked phylogeographic break between Atlantic and Mediterranean lobsters, we hypothesized that lobsters with dominant (>0.50) Atlantic ancestry were descended from historical stocking releases. Twenty Corsican lobsters were genotyped at 79 single nucleotide polymorphisms, and assignment analysis showed that the majority (13) had dominant Atlantic ancestry. This suggests that the hatchery stocking program carried out in Corsica during the 1970s, using individuals translocated from the Atlantic coast of France, has likely augmented local recruitment but at a cost of altering the genetic structure of the Corsican lobster population., Stocking is often used to supplement wild populations that are overexploited or have collapsed, yet it is unclear how this affects the genetic diversity of marine invertebrate populations. In this study, European lobsters caught around Corsica in the Mediterranean were genotyped and the results showed that a large proportion of lobsters have dominant Atlantic ancestry. This suggests that the stock enhancement programme carried out in Corsica during the 1970s, using individuals translocated from the Atlantic coast of France, has likely augmented recruitment but at a cost of altering the genetic structure of the Corsican lobster population. more...

As marine stocks and biodiversity are rapidly declining, the release of hatchery-reared individuals into the wild is a species conservation measure aiming at replenishing stocks of freshwater, anadromous and marine fish species. The aim of this study is to assess for the first time the post-release exploration behaviours, survival and dispersal in the wild of released hatchery-reared juveniles of D. dentex and S. umbra. For this purpose, twenty fish from each species were tagged with acoustic transmitters and released in a marine no-take zone located in Corsica (France). Most individuals were considered alive until their last detection (95% of S. umbra and 74% of D. dentex detected individuals). Fish were detected within the receiver array on average up to 11.3 (± 20.7) and 10.3 (± 10.3) days after being released for juveniles of D. dentex and S.umbra, respectively. Dentex dentex juveniles dispersed mostly southward along the shore whereas S. umbra juveniles tended to disperse along the shore both northward and southward from the acoustic receiver array. Before their rapid dispersion (i.e. within a few days) outside the studied zone, juveniles of both species displayed increasing cumulative MCP areas and increased their vertical niche revealing their gradual coverage and exploration of deeper habitats in the area. The results from our study highlighted that hatchery-reared juveniles of both species did not settle inside the studied area but seemed to start to acclimate to the natural environment. This work is a first step towards the assessment of the viability of restocking for both species. more...

The aim of this study was to obtain a better understanding of the exploitation pattern of the European lobster population in a fully representative small-scale fishery of the Mediterranean (Corsica, France) and to collect initial biological information on this species. Data were collected by scientific observers on board net fishing vessels for eight consecutive years from 2006 until 2013. Average annual catches were estimated at 6.7 t. Length frequencies indicated that exploitation focused on large individuals. Catch per unit of effort varied significantly as a function of month, fishing area and depth. Our approach to catch distribution revealed spatial heterogeneity with large catches in the south area. A fishery-independent survey was performed in 2013 and 2014 in west Cap Corse using 540 lobster traps; it showed an extremely low catch rate, confirming the low abundance for this area. This study provided new biological knowledge of a little-studied species in the Mediterranean. El objetivo de este estudio fue el de obtener una mejor comprensión del patrón de explotación y colectar datos iniciales de las poblaciones de bogavante europeo en una pesquera artesanal representativa del Mediterráneo (Córcega, Francia). Los datos fueron colectados por observadores científicos a bordo de embarcaciones de pesca durante 8 años consecutivos, de 2006 a 2013. Las capturas anuales fueron estimadas a 6,7 toneladas. La frecuencia de las tallas indica que la explotación se concentra en los individuos de gran tamaño. La CPUE varía de manera significativa en función del mes, la zona de pesca y la profundidad. La distribución de las capturas revela que hay una heterogeneidad espacial, con capturas de gran tamaño en la zona sur. Un monitoreo pesquero independiente fue llevado a cabo durante 2013 y 2014 en Cap Corse occidental empleando 540 trampas; éste mostró una tasa de captura extremadamente baja, lo que confirma la escasez de bogavante europeo en esta área. Este estudio aportó nuevos conocimientos a la biología de esta especie poco estudiada en el Mediterráneo. more...

The role of coastal macrophyte beds as a carbon sink is under debate. Various studies have provided global estimates of the carbon sequestration and stocks of macrophyte beds; however, the final fate of macrophyte debris exported from coastal beds remains uncertain, and must be determined in order to fully clarify the role of coastal vegetation as a carbon sink. Here we conducted bottom-trawl surveys to investigate the extensive and seasonal aggregation of exported macrophytes on the continental shelf and slope seafloor (40–1,800 m). Sunken macrophytes showed a clear seasonal trend with highest biomasses in summer. This was mainly caused by the most collected macrophyte species Sargassum horneri. Furthermore, we used numerical simulations to verify the link between sea-surface hydrographic condition and seafloor distribution of sunken macrophytes. Our results showed that S. horneri accumulated beneath the Kuroshio Extension current, which is the western boundary current of the North Pacific subtropical gyre. Overall, floating macrophytes that became transported offshore by a stable sea-surface current, such as the western boundary current, constitute an organic carbon pathway from coastal waters to the deep sea. Our findings suggest that these buoyant macrophytes can act as a biological pump to enhance oceanic carbon sequestration. more...

Experimental measurements were made in the laboratory to determine the swimming capacities of settlement-stage fish larvae of several Mediterranean coastal species collected from the nearshore waters of Corsica, France. Critical swimming speed (Ucrit , cm s-1 ) was measured to provide a realistic laboratory estimate of in situ swimming speed. Morphometric traits were measured to assess potential predictors of a species' swimming ability and, when possible, daily otolith increments were used to estimate age. Observed swimming speeds were consistent with other temperate species and demonstrated that the tested species are competent swimmers and not passive components of their environment. Morphological traits varied in their correlation with Ucrit across groups and species. Direct measurements of morphological traits were better predictors than calculated ratios. Pelagic larval duration had little relationship with swimming speed among species for which daily otolith increments were counted. In addition to expanding the database on swimming capacities of settlement-stage fish larvae in the Mediterranean Sea, this study also developed methods that simplify the assessment of larval fish swimming ability. Swimming speed data are essential for improving larval dispersal models and for predicting recruitment rates in coastal fish populations. more...

Spatio-temporal patterns of the gonadosomatic index (GSI) and life cycle stages of the sea urchin Paracentrotus lividus were studied at two Corsican near sites which differ in terms of protection status. The results highlighted an annual cycle of the GSI with spring spawning (between May and June) and presumed lesser autumn spawning (October or November). Spatial patterns revealed homogeneity in larval densities between the sites whereas differences were observed for settlers, recruits, sub-adults and adult stages. Temporal variability was detected for all stages with highly variable patterns for larval stage and settlement. This study suggests the presence of sporadic spawning and/or the arrival of allochthonous larvae to the sites. The recruitment intensity was highly variable between the two studied years; in 2016, the peak recorded was five-fold higher than in 2015. This study confirmed the importance of habitat diversity on the density of small individuals. The site’s protection status also influenced the structuring of P. lividus indirectly as the highest densities were recorded at the site where fishing was allowed. Finally, this work revealed the difficulty of observing the temporal evolution of the P. lividus life cycle in the natural environment. more...

Sea urchins were harvested for decades in many areas throughout its distribution range, potentially leading to population collapse. In France, the purple sea urchin Paracentrotus lividus is intensively harvested. Yet, the demography and population dynamics remained under-documented, particularly in Corsica. In this context, we have characterized the fluctuations in density of several size classes at 8 sites around the island, and assessed the genetic diversity and structuring of the population. Densities recorded lie between 0 and 2.18 (± 0.41) individuals.m-2 and spatio-temporal variabilities have also been highlighted. The study of the influence of vegetation cover on the size classes suggests that small- and medium- sized individuals prefer substrates of intermediate heights, whereas individuals with a diameter ≥ 5 cm are more often observed on encrusting substrates, and may be responsible for the continuation of this type of benthic community. The genetic study indicates a high genetic diversity with a low genetic structuring. The Ne values obtained are similar to those described in previous papers. Due to estimates of local contemporary Ne and the homogeneous genetic diversity, our data tend to show that the Corsican population of P. lividus is not overexploited. more...

The common dentex, Dentex dentex (L.), is an iconic marine coastal fish in the Mediterranean Sea. This study was performed in the Bonifacio Strait Natural Reserve (BSNR), (NW Mediterranean Sea). The aims were to: (1) evaluate temporal variation of the artisanal fishing of common dentex (2000–2012); (2) compare and quantify catch rates, fishing techniques and catch composition for artisanal and recreational fisheries, and determine the influence of management measures by both activities; and (3) estimate the production of both artisanal and recreational fisheries. Fishery data were collected from different artisanal fishing surveys (onboard fishing vessels and landings) and recreational fishing surveys (roving). The gears with the highest rates of exploitation were longline (3554 g per 100 hooks) and Trolling (351 g boat−1 h−1 ±SE), respectively, for artisanal and recreational fishing. This study showed that catches by both activities were quantitatively higher in partially protected areas than outside them. Production estimations suggest that the recreational fishery contributes significantly to fishing mortality and that it can magnify the negative effects of artisanal fisheries. Specific measures are needed for the sustainable fishery management of common dentex. more...

Among all available species, fish are a powerful model for risk-benefit assessments to study the effects of contaminants on human health. Gilthead seabream (Sparus aurata, Linnaeus 1758) and european seabass (Dicentrarchus labrax, Linnaeus 1758) are two species of great economic importance, representing very large production volumes in the Mediterranean. The objective of this study is (1) to analyze the concentrations of Trace Elements (TE) between wild and cultured seabream and seabass specimens, (2) to compare the determined concentrations with other studies, and (3) to increase the data about the potential risks to human health. Our results point to significant intra- and interspecies-specific differences between wild and cultured fish for several trace elements. Several strong and moderate inter-elemental correlations in fish muscle were observed through correlation analysis. In our study, the mean levels of trace elements were still below the standard safety values for fish intended for human consumption. The same results were reached for all the parameters analyzed (international legal limits, estimated weekly intake, provisional tolerable weekly intake, target hazard quotient, target cancer risk), with trace element levels in fish below those that could pose a risk to human health. Consequently, these fish can be considered safe for human consumption. A better understanding of the levels of trace elements in fish would also better inform consumers about the potential risks of exposure to contaminants. more...

International audience; The common dentex Dentex dentex (Linnaeus, 1758) is an iconic marine coastal fish in the Mediterranean Sea. It is a demersal sparid fish (0–200 m), that grows to a maximum length of 100 cm and a weight of 13 kg, with a relatively long life span (more than 20 years). As a high trophic level predator, it holds a key position in coastal marine food webs. The common dentex is of great economic importance for both artisanal (small-scale coastal fisheries) and recreational fishing. Despite its economic and ecological importance, scientific data on this species in its natural environment are still very scant. The global commercial catch of common dentex has fluctuated over the last 60 years on an interannual time scale, and has declined significantly since the 1990s. There are few data regarding fishing effort and total catch from recreational fishing for common dentex, but it appears that this species is particularly targeted by this activity. The common dentex is now classified as ‘‘vulnerable’’ in the Red List of Threatened Species in the Mediterranean Sea. This review summarizes the current literature on D. dentex in regard to biology, ecology, parasitology, population structure, commercial and recreational fishing, and management regulations. Future research directions to fill gaps in current knowledge are suggested. more...

International audience; The common dentex, Dentex dentex, is an iconic marine coastal fish of the Mediterranean Sea. Despite its economic and ecological importance, data on the population structure of this species are still very limited. The aim of this study was to identify the stock structure of the common dentex at relatively fine spatial scale around Corsica Island, using a combination of markers that have different spatial and temporal scales of integration: microsatellite DNA markers, otolith shape analysis and parasites communities. Microsatellite analysis indicated that there was no significant genetic differentiation in D. dentex between the four sampling sites around Corsica. Otolith shape analysis suggests one potential distinct population unit of D. dentex centered in one site (Cap Corse) varying in their degree of differentiation from those in the other zones. Multivariate analysis on parasite abundance data highlights to a lower extent two sites (Bonifacio and Galeria) with some connectivity between adjacent zones. The combination of these three markers together highlights the resulting three sites while giving complementary insights and an opportunity to compare their utility and potential to understand population interactions. A complex population structure around Corsican coasts is then proposed, providing a new perspective on common dentex fishery stock conservation and management strategies. more...

International audience; The striped bass ( Morone saxatilis ) supports a valuable recreational fishery and is among the most important piscivorous fish of the San Francisco Estuary. This species has suffered a significant decline in numbers over the past decades, and there is indication that contaminants are important contributors. Polycyclic aromatic hydrocarbons (PAHs) and polyhalogenated aromatic hydrocarbons (PHAHs) including PCBs and dioxins are widespread in the estuary, they typically bioaccumulate through trophic levels, reaching highest levels in top predators and are known to affect the fish health and development. The aim of this study was to investigate the dynamics of cytochrome P4501A ( Cyp1a ) induction simultaneously at different levels of biological organization (RNA transcription and protein synthesis) as a biomarker of exposure to PAHs and PHAHs. We utilized β-naphthoflavone (BNF) as a model PAH to induce Cyp1a responses in juvenile striped bass in both dose-response and time-response assessments and determined Cyp1a mRNA and protein levels. Significant responses were measured in both systems at 10 mg ΒΝF kg −1 , a concentration used for time-response studies. Messenger RNA levels peaked at 6 h post-injection, while protein levels increased progressively with time, significantly peaking at 96 h post-injection; both remaining elevated throughout the duration of the test (8 days). Our data suggest that rapid induction of gene transcription following exposure and subsequent cumulative protein synthesis could provide a useful means of identifying temporal variants in exposure to Cyp1a inducers in Morone saxatilis . The potential application of this combined Cyp1a gene and protein biomarker in this species for field studies is discussed. more...

Spontaneous swimming activity of O-group common sole (Solea solea) was evaluated using a video-tracking system under laboratory conditions. An experiment was conducted during two consecutive days on individuals sampled in June, July, September and November (2004) in a coastal nursery ground (Pertuis Charentais, Bay of Biscay, France). The measured behavioural variables were: distance travelled and frequency of occurrence of burying, swimming and immobility. O-group sole showed a relatively clear circadian activity in line with the artificial light conditions (day, twilight and night). Swimming activity of O-group sole decreased drastically from June to July, thereafter remaining at a very low level in September and November. Such important changes reflect the transition between the exploratory behaviour of the post-colonization period and a well established sedentary behaviour remaining until the onset of winter. These results highlight the potential limitation in habitat use capacities of O-group sole once settled in coastal nursery grounds. more...

The common dentex, Dentex dentex (Linnaeus, 1758), is an iconic coastal fish found in the Mediterranean Sea. Despite its ecological and economic importance, scientific data on its exploitation are scarce, especially off Corisca. The aims of our study were to: (1) analyze the relationship between the catch per unit effort (CPUE, by weight and number) and possible factors driving the trends observed; (2) examine temporal and spatial trends in CPUE; (3) examine the spatial distribution of fishing effort; and (4) compare the size distribution and age structure of catches. Sampling was conducted on fishing vessels operating from the main fishing harbors and in the main fishing sectors off Corsica between 2009 and 2013. CPUE varied spatiotemporally, but overall displayed annual stability. CPUE varied significantly as a function of month, strata, and depth. A seasonal pattern was observed with high catches during the spawning period (May) when size classes were mainly composed of mature individuals. Length and age frequency histograms after the spawning period (June–September) indicated that exploitation focused on small/young, immature individuals. Our spatial approach revealed a heterogeneous catch distribution and identified important exploitation areas. Results suggest that a combination of management tools and specific measures to safeguard the reproductive potential of this species should be implemented. more...

Digenean metacercariae of 0 year group common sole Solea solea (n = 70) were more abundant in the embayed nursery of the Pertuis Charentais than in the Tagus estuary nursery. Macroparasite assemblages of adult sole (n = 119) displayed only one species in common between the Bay of Biscay and the Portuguese coast continental shelves. These data highlighted the potential use of macroparasites as biological tags in various aspects of common sole ecology. (C) 2007 The Authors. more...

The effect of a marine protected area on the Lamellodiscus spp. monogenean community was tested by comparing the communities of parasites of Diplodus sargus inside and outside of the area. A total of 104 D. sargus were dissected harbouring 1280 monogeneans from the genus Lamellodiscus and belonging to 11 species. No modification in the global parasite community linked with the protection of the host populations was revealed. The most abundant and less specific parasite species, Lamellodiscus elegans, however, increased its abundance in the protected area. A significant relationship was found between parasite host range and the percentage of infected hosts. A significant relationship also occurred between epidemiological and genetic distances for the parasite species found. The results are discussed in term of parasite success and specificity and the importance of taking into account parasitism in the biological conservation of hosts. more...

The Strait of Bonifacio constitutes one of the rare transboundary Marine Protected Areas (MPA) of the Mediterranean Sea (between Sardinia, Italy and Corsica, France). Based on the hypothesis that no-take zones will produce more fish larvae, compared to adjacent fished areas, we modeled the outcome of larvae released by coastal fishes inside the no-take zones of the MPA in order to: (i) characterize the dispersal patterns across the Strait of Bonifacio; (ii) identify the main potential settlement areas; (iii) quantify the connectivity and the larval supply from the MPAs to the surrounding areas. A high resolution hydrodynamic model (MARS 3D, Corse 400m) combined to an individual based model (Ichthyop software) was used to model the larval dispersal of fish following various scenarios (Pelagic Larval Duration PLD and release depth) over the main spawning period (i.e. between April and September). Dispersal model outputs were then compared with those obtained from an ichthyoplankton sampling cruise performed in August 2012. There was a the significant influence of PLD to the connectivity between coastal areas. The synchronization between spawning and hydrodynamic conditions appeared to be determinant in the larval transport success. Biotic and abiotic parameters affecting the dispersal dynamic of fish larvae within the Strait of Bonifacio were identified and synthesis maps were established as a tool for conservation planning. more...

Growth-related characters, condition factor, and genetic differentiation were investigated for a single cohort of young-of-the-year (YOY) sole within and among nurseries with differing levels of heavy metals (Cd, Cu and Zn) contamination in the two Charentais Straits, Bay of Biscay, France. Analyses were performed when individuals recruited (May), then after a full summer spent in each nursery (October). Levels of phenotypic and genetic diversity were compared, together with genetic differentiation at a candidate metallothionein (MT) locus and three putatively neutral microsatellite loci. No phenotypic or genetic differentiation was detected among nurseries in May, but significant variation at each phenotypic trait and at the multilocus level in October (P < 0.001). Single locus analysis demonstrated that only the MT locus was significantly differentiated among nurseries, whether corrected for null alleles or not ( = 0.0401 and (theta) over cap (corr.FreeNA) = 0.0326. respectively; P < 0.001). Results indicate that phenotypic differences among YOY sole nurseries present a molecular correlate acting at identical spatio-temporal scales among nurseries, potentially reflecting differential selective pressure among nurseries in response to contamination. (C) 2011 Elsevier Ltd. All rights reserved. more...

This study focused on the spatio-temporal variation in the host-parasite system, 0-group sole-digenean metacercariae, in nearshore coastal areas at relatively small spatial scale. 0-group soles were sampled using a standard beam trawl in April, May, June, August and October 2005 at nine different sites in the Pertuis Charentais area (Bay of Biscay, France). Sole density, size, Fulton's condition factor K and digenean metacercariae communities were analysed. 0-group sole concentrated in shallow and muddy areas where they accumulated digenean metacercariae. Parasite communities displayed strong spatial patterns tightly linked to the distribution of the first intermediate mollusc hosts. These parasitological data suggest that 0-group sole during their first period of growth are mainly sedentary with limited movements between the different parts of the habitat. Size and density data revealed spatial heterogeneity in terms of habitat quality so that a limited zone (Aiguillon Bay) within the study area could be identified as sensu stricto nursery habitat for 0-group sole. The use of digenean metacercariae as natural tags appears as a novel powerful tool to evaluate habitat use and movements of juvenile flatfish, which could find applications in fisheries and coastal zone management programs. (C) 2009 Elsevier B.V. All rights reserved. more...

We sampled 0-group sole juveniles (N = 174) in September and October 2003 in 9 major nurseries located along the French Atlantic coast (English Channel and Bay of Biscay). 0-group sole were infected with 3 genera of digenean metacercariae, Timoniella spp. (Acanthostomidae), Prosorhynchus crucibulum and Prosorhynchus sp. A (Bucephalidae), Podocotyle sp. (Opecoelidae), and an unidentified species of Digenea. Parasite infection levels in the English Channel nurseries were lower, and the community composition was different from Bay of Biscay nurseries. We hypothesize that the difference between geographic areas was due to differences in first intermediate host communities and, to a lesser extent, because of lower temperatures in the English Channel compared to the Bay of Biscay. For the Bay of Biscay nurseries, mean total parasite abundance was strongly negatively correlated with mean annual river flow. This relationship may be the result of the more upstream location of 0-group sole nurseries in estuaries so that fish were further from local points of parasite transmission than those in embayed nurseries. Digenean metacercariae load may be influenced by 3 major local factors, i.e. abundance and proximity of the first intermediate hosts and cercariae dispersal capacities. more...

Little attention has been paid to flatfish parasitism as a potential factor of variation in year-class strength. The aim of this study was to evaluate the relationship between parasitic infection and nutritional condition of young-of-year (YOY) common sole. Sole were collected monthly from May (early settlement) to November 2004 in a mussel pole culture area, using a push-net or a trawl, and dissected for parasite identification and counts. Total lipids were extracted from the whole body and lipid classes quantified. Triacylglycerols to sterols (free form) ratio (TAG/ST) was used as an index of nutritional status. Digenean metacercariae infection, characterized by two dominant genera, displayed clear seasonal dynamics and the highest records yet reported for sole. Prevalence (P%) and mean abundance (Ab SE) increased for Timoniella spp. (Acanthostomidae) from May (P% = 22% Ab = 1.9 +/- 1.1) to August (P% = 100%; Ab = 51.2 +/- 10.4), and for Prosorhynchus spp. (Bucephalidae) from June (P% = 8%; Ab =1.9 +/- 0.0) to August (P%=100%; Ab=19.5 +/- 1.7). Epidemiological values reached a plateau after August. In this shellfish-dominated nursery area, YOY sole accumulated metacercariae in the presence of the first intermediate hosts which live in the same habitat. Total lipids decreased significantly from May to June and then remained constant until autumn, indicating a change in the proximate composition of YOY during this high growth period. Mean ( +/- SD) TAG/ST ratio increased from very low values in May-July (0.10 on average) to a peak in September (0.57 +/- 0.31) and then fell back to values as low as before. YOY sole only stored energy as TAG prior to autumn. No relationship was found between YOY parasitic infection levels and lipid condition indices. However, the poor nutritional status and heavy infection level observed in November could dramatically lower over-winter survival of the YOY remaining in this shallow part of the nursery. (c) 2006 Elsevier B.V. All rights reserved. more...