Littérature scientifique sur le sujet « Paracentrotus lividus – Corse (France) »

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.

The temperate Northwest Pacific brown alga Rugulopteryx okamurae (Dictyotales, Phaeophyceae) was first discovered in 2002 in the Mediterranean Sea in the Thau coastal lagoon (Occitania, France) and then again in 2015 along the southern side of the Strait of Gibraltar, where it was assigned with invasive status. We report here on the first occurrence of the species in the Northwest Mediterranean Sea in Calanques National Park (Marseille, France) in 2018. By 2020, a large population had developed, extending over 9.5 km of coastline, including highly protected no-take zones. The seafood trade, with R. okamurae used as packing material for sea urchin Paracentrotus lividus shipments from Thau Lagoon, could be the vector of its introduction into the Marseille area. As observed in the Strait of Gibraltar, R. okamurae is spreading rapidly along the Marseille coasts, suggesting an invasive pathway. The subtidal reefs are densely carpeted with R. okamurae, which overgrows most native algal species. Fragments of the alga are continuously detached by wave actions and currents, sedimenting on the seabed and potentially clogging fishing nets, and thus, impacting artisanal fishing or washing up on the beaches, where they rot and raise concern among local populations.

The distribution, abundance and feeding behaviour of sea urchins (Paracentrotus lividus, Psammechinus miliaris, Sphaerechinus granularis) and the macro-algal biomass were assessed in two maerl beds within a north-east Atlantic coastal ecosystem (Bay of Brest, Brittany, France). To study the possible control of herbivorous sea urchins on the macrophytic algae, one maerl bed under the influence of urban sewage (northern site) was compared to one less influenced by urban and industrial outlets (southern site). Macrophytic biomass in the northern site was estimated as 40-fold higher than in the southern site where sea urchins were, on average, 38-times more numerous. Preliminary results support the hypothesis that grazing of sea urchin, even in low densities, can be a factor regulating the macrophytic biomass on maerl beds except in too nutrient enriched environments. So in the northern basin of the Bay, data pointed out the role of anthropogenic impacts on macrophytic biomass increase which was concomitant with the progressive disappearance of sensitive herbivorous species like sea urchins, both processes result in change in the ecosystem.

A method for a qualitative analysis of sea urchin diet is based on the characterization of the photosynthetic pigment indices of the major algal groups in the sea urchin gut. The pigments were separated by reverse-phase high performance liquid chromatography (RP-HPLC). This study demonstrated that HPLC is a better method to estimate chlorophyll-a in the gut contents than the conventional spectrophotometric methods which overestimate the amounts by including chlorophyll-a breakdown products. Three sea urchins species, Paracentrotus lividus, Psammechinus miliaris and Sphaerechinus granularis, settled on the loose-lying coralline algae (maerl) in the Bay of Brest (France), were used in this study. The algal pigments identified within the gut contents included chlorophylls-a, -b, -c, fucoxanthin, lutein, βε-carotene and ββ-carotene. The presence of chlorophylls and carotenoid biomarkers was used to characterize the three algal groups: Rhodophyceae, Chlorophyceae, Phaeophyceae in estimating sea urchin diet. The pigment analysis reported here demonstrated that the three species of sea urchins investigated mainly consumed Rhodophyceae which dominate the epibenthic flora in the study area.

Seasonal and annual variations in the distribution and abundance of echinoderm larvae (early to post-larvae of principally echinoids and ophiuroids), were determined from a series of plankton net tows taken at three stations in the Bay of Villefranche (France) and along a radial transect of 28 nautical miles (52 km), from the Bay to half-way to Corsica, between 1984 and 1988. Spatial distribution of six echinoderm species have been mapped. For the echinoids, Paracentrotus lividus and Arbacia lixula, spawning takes place twice a year and appears to be synchronous because larval cohorts were comprised of distinct age-classes both near and far from the coast. Recruitment for these species is, therefore, thought to occur at well-defined periods. In contrast, the ophiuroid species studied (Amphiura filiformis, Ophwthrix fragilis, Ophiopluteus bimaculatus and O. compressus) spawn several times per year with a relatively short period in late spring and a prolonged spawning between the end of autumn and winter. These later results are consistent with the presence of mixed size-classes of larvae either from the nearby coast or offshore. Recruitment for these ophiuroids appears to be much more variable and spread over time.

Les éléments traces font partis des contaminants les plus répandus dans l’écosystème marin. Au-dessus de seuils critiques, tous les éléments traces présentent un danger potentiel pouvant entraîner des perturbations à l’échelle cellulaire et individuelle, mais aussi au niveau de la population ou de l’écosystème. En Méditerranée, la Corse a longtemps été considérée comme une zone subissant de faibles pressions anthropiques. De par ses caractéristiques écologiques, sa haute tolérance aux contaminants et sa capacité à bioaccumuler des éléments traces, l’oursin violet Paracentrotus lividus (Lamarck, 1816) est reconnu en tant que bioindicateur. L’objectif de ce travail de thèse a consisté à mieux comprendre les variations des contaminations en éléments traces en Corse ainsi que leurs effets chez un organisme emblématique,Paracentrotus lividus. Une évaluation de la contamination en éléments traces classiques et émergents a été menée sur les gonades d’oursins. Dans ce cadre, plusieurs prélèvements en mer ont été effectués afin de déterminer les principaux éléments traces susceptibles d’être bioaccumulés par l'oursin adulte et les variations spatio-temporelles de ces contaminants. Ces travaux ont mis en évidence des régions en Corse présentant des concentrations en éléments traces plus élevées dues aux fonds géochimiques associés aux pressions anthropiques. Des variations saisonnières ont également été décelées avec des concentrations plus faibles durant la saison estivale. Ces variations sont notamment liées au cycle de reproduction de l’oursin et démontrent l’importance des facteurs biotiques dans l’évaluation des niveaux de contamination. Les analyses biochimiques des oursins adultes suggèrent que le stress oxydatif induit par les contaminations mesurées n'a pas d'impact direct sur leur santé. Les bioessais menés sur les stades larvaires de l’oursin ont permis d’évaluer les effets de différentes contaminations en éléments traces. Ces contaminations ont induit des malformations ainsi qu’un ralentissement de la croissance, voire une inhibition du développement larvaire. En parallèle, des recherches sur les réponses au stress des différents stades larvaires ont permis de souligner la grande capacité des larves à répondre au stress oxydatif, mais également l’importance des géniteurs dans les études utilisant les larves d’oursin. Ces expérimentations innovantes sont les premières à s’intéresser aux effets d’une combinaison aussi importante d’éléments traces sur l’ensemble du cycle larvaire de l’oursin. Le présent travail pourrait renforcer d’autres outils de diagnostic et de suivi de la qualité des eaux côtières en vue d’améliorer la qualité écologique des eaux marines
Trace elements are among the most commoncontaminants in the marine ecosystem. Beyond critical thresholds, all trace elements present apotential danger that can lead to disturbances at the cellular and individual level, but also at thepopulation or ecosystem level. In the Mediterranean Sea, Corsica Island has long been considered anarea of low anthropic pressure. Due to its ecological characteristics, its high tolerance to contaminantsand its ability to bioaccumulate trace elements, the sea urchin Paracentrotus lividus (Lamarck, 1816)is recognized as a bioindicator. The aim of this thesis was to better understand the variations of traceelement contamination in Corsica and their effects on an emblematic organism, Paracentrotus lividus.An assessment of the contamination of classical and emerging trace elements was conducted on seaurchin gonads. In this context, several samples were collected in order to determine the main trace elements susceptible to be bioaccumulated by the adult sea urchin and the spatio-temporal variationsof these contaminants. This research has highlighted areas in Corsica with higher trace elementconcentrations due to geochemical backgrounds associated with anthropogenic pressures. Seasonalvariations were also identified with lower concentrations during the summer season. These variationsare mainly due to the reproduction cycle of the sea urchin and show the importance of biotic factorsin the evaluation of contamination levels. Biochemical analyses of adult sea urchins suggest that theoxidative stress induced by the measured contaminations has no direct impact on their health.Bioassays performed on larval stages of sea urchins were used to evaluate the effects of several traceelement contaminations. These contaminations induced malformations and a slowing of thedevelopment. In addition, research on the stress responses of the different larval stages hashighlighted the high capacity of larvae to respond to oxidative stress, but also the importance ofspawners in studies using sea urchin larvae. These innovative experiments are the first to investigatethe effects of such important combinations of trace elements on the entire larval cycle of the seaurchin. This present work could strengthen other tools for diagnosing and monitoring coastal waterquality in order to improve the ecological quality of marine waters

Les oursins comestibles paracentrotus lividus (lamarck, 1816) et loxechinus albus (molina, 1872) ont ete l'objet d'une peche intensive depuis plusieurs annees, p. Lividus sur les cotes francaises et l. Albus sur les cotes chiliennes. A l'heure actuelle, les deux especes montrent des signes de surexploitation, notamment, la disparition des aires de peche et des individus de taille commerciale. L'etude entreprise sur p. Lividus dans l'archipel du frioul et sur la cote bleue (reserve marine de carry et hors de la reserve) a permis d'evaluer l'etat des populations et des stocks et de caracteriser les populations d'un point de vue biometrique. Dans l'archipel du frioul, la densite moyenne est de 0. 5 a 19 individus/m#2 sur substrats rocheux, et de 3 a 10 individus/m#2 dans l'herbier a posidonia oceanica. Dans la reserve, ces valeurs sont de 6 a 36 individus/m#2 et de 4 a 10 individus/m#2 respectivement. Hors de la reserve, densite moyenne est de 75 individus/m#2 sur substrat rocheux et de 19 individus/m#2 dans l'herbier. La taille moyenne des oursins, au frioul et sur la cote bleue (hors reserve) est inferieure a 40 mm. Par contre, dans la reserve la taille moyenne est superieure a 40 mm. Dans l'archipel du frioul, la biomasse moyenne humide par metre carre, a ete estimee a 250 g/m#2 dont 25 g/m#2 correspondent a la biomasse moyenne des oursins commercialisables (0. 5 individus/m#2 de taille superieure ou egale a 50 mm) ; dans la reserve marine la biomasse moyenne a ete estimee a 440 g/m#2 dont 220 g/m#2 correspondent a la biomasse moyenne des oursins commercialisables (3-4 individus/m#2 de taille superieure ou egale a 50 mm). Trois strategies de reconstitution des stocks peuvent etre envisagees: i) la creation des espaces proteges ; cependant la population de p. Lividus de la reserve marine de carry presente une densite moins elevee que celles situees dans une zone temoin hors de la reserve, ces resultats pourraient etre expliques par l'augmentation des predateurs apres la mise en reserve ; ii) la transplantation d'individus, les experiences realisees chez p. Lividus d'un milieu pollue (cortiou) transplantes vers un autre non pollue (cote bleue) ont montre que les pertes d'individus sont de l'ordre de 30% et la principale cause a ete la predation ; les indices physiologiques (gonadique et de repletion) sont plus eleves a la fin de l'experience, on observe, par contre, une diminution de la concentration des metaux lourds dans les gonades des oursins a la fin de l'experience, notamment du fer (-50%) et du cuivre (-40%) ; la concentration du zinc est superieure (x10) dans les gonades des femelles que dans celles des males ; iii) la production et le lacher de juveniles est une troisieme strategie ; les experiences realisees chez l. Albus ont permis de definir des protocoles pour la production et l'elevage des larves et des juveniles (temperature, salinite, densite d'elevage, alimentation) et pour le lacher de ces derniers (taille, densite, periode optimale). Ces trois strategies peuvent etre appliquees simultanement chez une espece dans le cadre d'un programme global de reconstitution de stocks