Isolation of 12 polymorphic tetranucleotide microsatellite markers of the leaf beetle Ophraella communa, a promising Ambrosia biocontrol agent also in Europe

Following its first record in Europe in 2013, the North American ragweed leaf beetle Ophraella communa, used already as a most successful biocontrol agent against common ragweed in China, is spreading rapidly, asking for a detailed analysis of the potential benefit and risk of this introduction for Europe. Here, we report twelve specific and polymorphic tetranucleotide microsatellite markers, which can be used for redrawing its global invasion history and spread across native and introduced ranges. The high level of polymorphism (i.e. from 4 to 18 alleles per locus) and the genetic variation detected within and between one native and two introduced populations provide adequate statistical power for elucidating the beetle’s invasion process

Specific niche requirements underpin multidecadal range edge stability, but may introduce barriers for climate change adaptation

Aim: To investigate some of the environmental variables underpinning the past and present distribution of an ecosystem engineer near its poleward range edge. Location: >500 locations spanning >7,400 km around Ireland. Methods: We collated past and present distribution records on a known climate change indicator, the reef-forming worm Sabellaria alveolata (Linnaeus, 1767) in a biogeographic boundary region over 182 years (1836–2018). This included repeat sampling of 60 locations in the cooler 1950s and again in the warmer 2000s and 2010s. Using species distribution modelling, we identified some of the environmental drivers that likely underpin S. alveolata distribution towards the leading edge of its biogeographical range in Ireland. Results: Through plotting 981 records of presence and absence, we revealed a discontinuous distribution with discretely bounded sub-populations, and edges that coincide with the locations of tidal fronts. Repeat surveys of 60 locations across three time periods showed evidence of population increases, declines, local extirpation and recolonization events within the range, but no evidence of extensions beyond the previously identified distribution limits, despite decades of warming. At a regional scale, populations were relatively stable through time, but local populations in the cold Irish Sea appear highly dynamic and vulnerable to local extirpation risk. Contemporary distribution data (2013–2018) computed with modelled environmental data identified specific niche requirements which can explain the many distribution gaps, namely wave height, tidal amplitude, stratification index, then substrate type. Main conclusions: In the face of climate warming, such specific niche requirements can create environmental barriers that may prevent species from extending beyond their leading edges. These boundaries may limit a species’ capacity to redistribute in response to global environmental change

Estimation des stocks de palourdes sur les côtes oléronnaises du bassin de Marennes-Oléron

La vénériculture a connu un essor important dans les années 1980, grâce à la mise en place de techniques de reproduction et de grossissement pour la palourde croisée japonaise. Cependant, la maladie de l'anneau brun, qui a été la cause de fortes mortalités, ainsi que la concurrence intemationale provoquant une chute des cours de la palourde, ont été à l'origine du coup d'arrêt de la vénériculture dès la fin des années 80. A l 'heure actuelle, la vénériculture reste une activité marginale. Néanmoins, le long des côtes françaises, et notamment au niveau du bassin de Marennes-Oléron, des populations de palourdes se sont développées à l'état naturel. Cela entraîne une activité de pêche professionnelle et touristique relativement importante. Dans le but de gérer convenablement les stocks naturels de palourdes, le Comité Régional des Pêches Maritimes et des Elevages Marins Poitou-Charentes (CRPMEM) a sollicité l'IFREMER pour réaliser une campagne d'estimation des stocks sur les zones de pêche professionnelle, de Bonne Anse (164 tonnes déclarées en 2008) et de Bellevue (7,5 tonnes déclarées en 2008) (source IFREMER). Par ailleurs, en coopération avec l'association Iodde (Ile d'Oléron Développement Durable Environnement), une campagne d'estimation des stocks sur la zone de pêche à pied de Saint-Trojan a été réalisée. A partir du nombre de pêcheurs actifs sur la zone de pêche, d'une estimation du temps moyen de pêche (lh30) et du poids moyen prélevé par personne et par heure (environ 2 kg/h), Iodde a estimé pour l'année 2007, la récolte de palourdes par les particuliers entre 48 et 58 tonnes sur le site de Manson à Saint-Trojan (Iodde, 2007). Alors que des études sur les stocks de palourdes ont été réalisées pour le bassin d'Arcachon (Caill-Milly et al., 2003, 2006), pour la rivière de Pont l'Abbé (Dimeet et al., 2008) et le Golfe du Morbihan (D'Hardivillé et al., 2008), aucune étude de ce genre n'a été menée sur le bassin de Marennes-Oléron. Ce travail devait initialement se réaliser avec le soutien logistique d'un navire de surface équipé d'une grue hydraulique permettant d'actionner une benne Hamon. La non-disponibilité de ce matériel a réorienté la méthodologie et les objectifs du stage. La technique de prélèvement avec la benne Hamon préconisée par Caill-Milly et utilisée dans le Golfe du Morbihan a été remplacée par la méthode des cadrats utilisée pour la rivière de Pont l'Abbé. Cette technique, plus lourde à mettre en oeuvre a de fait limité les zones de travail. Il n'a été possible d'exploiter que 2 des 3 zones citées sur des superficies plus faibles que prévues. L'objectif a donc été d'estimer les stocks de palourdes en termes d'abondance et de biomasse sur ces deux zones

Primary production and functioning of intertidal communities dominated by Fucus canopy

En milieu intertidal rocheux, les communautés dominées par des canopées d'algues brunes (Phaeophyceae) sont particulièrement répandues. Malgré leur accessibilité, leur fonctionnement reste encore largement méconnu. En particulier, l'influence de la saisonnalité et du gradient d'émersion sur le métabolisme, le réseau trophique ou encore le processus de succession a été peu étudiée. Ce travail de thèse a donc eu pour objectif d'analyser le fonctionnement de deux communautés de Fucus établies à des niveaux marégraphiques différents, en portant une attention particulière aux conditions environnementales. Sur les côtes bretonnes (France), les communautés de Fucus vesiculosus Linnaeus et de Fucus serratus Linnaeus sont respectivement caractéristiques des étages médiolittoral moyen et inférieur. Des mesures de métabolisme (production primaire et respiration) réalisées in situ à différentes périodes de l'année ont mis en évidence une forte influence de la saisonnalité et le rôle primordial de la canopée dans les flux de carbone. Le métabolisme s'est avéré être plus élevé à l'émersion qu'à l'immersion, où l'intensité lumineuse constitue régulièrement un facteur limitant pour la production primaire. Par une approche de modélisation basée sur ces mesures et sur des données environnementales acquises à haute fréquence, un bilan annuel de production primaire a été calculé pour chaque communauté. Ces bilans confirment que ces systèmes sont fortement productifs et permettent de préciser leur régulation à l'échelle des cycles de marées. Le réseau trophique de ces communautés, analysé via les isotopes stables du carbone et de l'azote, apparait basé sur l'utilisation de nombreuses sources.Along intertidal rocky shores, communities dominated by canopy-forming brown algae (Phaeophyceae) are particularly widespread. Their functioning is however largely understudied, especially concerning the influence of seasonality and shore height on primary production and respiration, on food webs or on successional process. The aim of this study was to investigate the functioning of two intertidal Fucus communities which are established at different tidal levels. During this study, a special consideration was given to the effects of environmental conditions. On the coasts of Brittany (France), communities dominated by Fucus vesiculosus Linnaeus and Fucus serratus Linnaeus are characteristic of mid-intertidal and low mid-intertidal levels, respectively. In situ measurements of metabolism (primary production and respiration) carried out at different periods of a year highlighted a strong seasonal influence on carbon fluxes and emphasized the importance of canopies in the metabolism of whole communities. Metabolism was higher during emersion than during immersion periods, for which light intensity regularly limits the primary production. Based on these measurements and on high-frequency measurements of environmental parameters, an annual primary production was calculated by modelling for both communities. These annual estimations confirmed that these communities are among the most productive systems of coastal region and specify their regulation at the tidal cycles scale. Food webs, which were analysed through carbon and nitrogen stable isotopes, are based on the use of almost all available sources of organic matter by consumers, and revealed a strong conservation of food webs across seasons. Thecolonisation survey of bare substrates shows that Fucus species improve the settlement success of numerous species and increase rapidly primary production of whole assemblages. Overall, despite some differences in metabolism and successional sequences according to the shore height at whichthey are located, these communities exhibited similar functioning due to the canopy which damns the environmental conditions

Production primaire et fonctionnement de communautés intertidales à canopée de Fucus

Along intertidal rocky shores, communities dominated by canopy-forming brown algae (Phaeophyceae) are particularly widespread. Their functioning is however largely understudied, especially concerning the influence of seasonality and shore height on primary production and respiration, on food webs or on successional process. The aim of this study was to investigate the functioning of two intertidal Fucus communities which are established at different tidal levels. During this study, a special consideration was given to the effects of environmental conditions. On the coasts of Brittany (France), communities dominated by Fucus vesiculosus Linnaeus and Fucus serratus Linnaeus are characteristic of mid-intertidal and low mid-intertidal levels, respectively. In situ measurements of metabolism (primary production and respiration) carried out at different periods of a year highlighted a strong seasonal influence on carbon fluxes and emphasized the importance of canopies in the metabolism of whole communities. Metabolism was higher during emersion than during immersion periods, for which light intensity regularly limits the primary production. Based on these measurements and on high-frequency measurements of environmental parameters, an annual primary production was calculated by modelling for both communities. These annual estimations confirmed that these communities are among the most productive systems of coastal region and specify their regulation at the tidal cycles scale. Food webs, which were analysed through carbon and nitrogen stable isotopes, are based on the use of almost all available sources of organic matter by consumers, and revealed a strong conservation of food webs across seasons. Thecolonisation survey of bare substrates shows that Fucus species improve the settlement success of numerous species and increase rapidly primary production of whole assemblages. Overall, despite some differences in metabolism and successional sequences according to the shore height at whichthey are located, these communities exhibited similar functioning due to the canopy which damns the environmental conditions.En milieu intertidal rocheux, les communautés dominées par des canopées d'algues brunes (Phaeophyceae) sont particulièrement répandues. Malgré leur accessibilité, leur fonctionnement reste encore largement méconnu. En particulier, l'influence de la saisonnalité et du gradient d'émersion sur le métabolisme, le réseau trophique ou encore le processus de succession a été peu étudiée. Ce travail de thèse a donc eu pour objectif d'analyser le fonctionnement de deux communautés de Fucus établies à des niveaux marégraphiques différents, en portant une attention particulière aux conditions environnementales. Sur les côtes bretonnes (France), les communautés de Fucus vesiculosus Linnaeus et de Fucus serratus Linnaeus sont respectivement caractéristiques des étages médiolittoral moyen et inférieur. Des mesures de métabolisme (production primaire et respiration) réalisées in situ à différentes périodes de l'année ont mis en évidence une forte influence de la saisonnalité et le rôle primordial de la canopée dans les flux de carbone. Le métabolisme s'est avéré être plus élevé à l'émersion qu'à l'immersion, où l'intensité lumineuse constitue régulièrement un facteur limitant pour la production primaire. Par une approche de modélisation basée sur ces mesures et sur des données environnementales acquises à haute fréquence, un bilan annuel de production primaire a été calculé pour chaque communauté. Ces bilans confirment que ces systèmes sont fortement productifs et permettent de préciser leur régulation à l'échelle des cycles de marées. Le réseau trophique de ces communautés, analysé via les isotopes stables du carbone et de l'azote, apparait basé sur l'utilisation de nombreuses sources

Assessing the physiological responses of the gastropod Crepidula fornicata to predicted ocean acidification and warming

Organisms inhabiting coastal waters naturally experience diel and seasonal physico‐chemical variations. According to various assumptions, coastal species are either considered to be highly tolerant to environmental changes or, conversely, living at the thresholds of their physiological performance. Therefore, these species are either more resistant or more sensitive, respectively, to ocean acidification and warming. Here, we focused on Crepidula fornicata, an invasive gastropod that colonized bays and estuaries on northwestern European coasts during the 20th century. Small (4.5 cm in length), sexually mature individuals of C. fornicata were raised for 6 months in three different pCO2 conditions (390 μatm, 750 μatm, and 1400 μatm) at four successive temperature levels (10°C, 13°C, 16°C, and 19°C). At each temperature level and in each pCO2 condition, we assessed the physiological rates of respiration, ammonia excretion, filtration and calcification on small and large individuals. Results show that, in general, temperature positively influenced respiration, excretion and filtration rates in both small and large individuals. Conversely, increasing pCO2 negatively affected calcification rates, leading to net dissolution in the most drastic pCO2 condition (1400 μatm) but did not affect the other physiological rates. Overall, our results indicate that C. fornicata can tolerate ocean acidification, particularly in the intermediate pCO2 scenario. Moreover, in this eurythermal species, moderate warming may play a buffering role in the future responses of organisms to ocean acidification. -- Keywords : Calcification ; Coastal system ; Invasive species ; Metabolism ; Mollusk ; pCO2 ; Temperature

Estimation des stocks de palourdes Ruditapes decussatus, Ruditapes philippinarum sur l'estran oléronais du bassin de Marennes-Oléron. Juin 2009

On French coast, Manila clam is a bivalve subject of a large activity recreational and professional hand harvest. Two species are represented in France, European Manila clam Ruditapes decussatus (native) and Japanese Manila clam Ruditapes philippinarum (introduced). Predominance of this last species (more than 90 % of number and biomass), earn them the status of invasive species. Contrary to Arcachon bay, Pont l’Abbé River or Morbihan bay, an estimation campaign of Manila clams stock on Marennes-Oléron bay had never been carried out. The objective of this study: estimate, in number and biomass, the Manila clams stock of two areas. The first affect recreational hand harvest, on Saint-Trojan shore (0.8 km²) whereas the second scopes professional hand harvest, on Bellevue area (0.77 km²). This last one is integrated into the Moëze-Oléron natural reserve. With the Hamon skip unavailable, the usual sampling method couldn’t be used. The samples had been realized on foot, according to the quadrat method. To Saint-Trojan, the Manila clams stock is estimated at 88.7 tones (± 67.3) to 14.56 million (±11.23) of individual. The result to Bellevue is 150.7 tones (± 114.9) to 39.42 million (± 28.66) of individual. The stocks of commercial Manila clams are respectively 18.2 and 53.8 tones. Bellevue, with a commercial Manila clams density of 0.76 t/ha is better than Arcachon bay and Saint-Trojan (0.23 t/ha). Yet, it’s lower than Pont l’Abbé River or Morbihan bay. Analysis of histograms of the size frequency using FISAT II (a FAO method software), was carried to establish the population age structure. The Bellevue Manila clams stock is of great interest to the professional hand harvest whereas to Saint-Trojan, the low level of stock could point out a resource management problemLa palourde fait l’objet sur les côtes françaises d’une importante activité de pêche pieds, plaisancière et professionnelle. Deux espèces sont principalement représentées en France, la palourde européenne Ruditapes decussatus (autochtone) et la palourde japonaise Ruditapes philippinarum (allochtone). La prédominance de cette dernière (plus de 90 % des effectifs et de la biomasse) lui assure la qualification d’espèce invasive. Aucune campagne d’estimation des stocks de palourdes n’avait encore été réalisée sur le bassin de Marennes-Oléron, contrairement au bassin d’Arcachon, à la rivière de Pont l’Abbé et au Golfe du Morbihan. L’objectif de cette étude a été d’estimer, en effectifs et en biomasse, les stocks de palourdes de deux zones du bassin : l’estran de Saint-Trojan (0,8 km²) pour la pêche à pied récréative et celui de Bellevue (0,77 km²) pour la pêche professionnelle. Ce dernier fait parti de la réserve naturelle de Moëze-Oléron. La méthode d’échantillonnage avec la Benne Hamon n’ayant pu être mise en oeuvre, c’est à pied que les prélèvements ont été effectués selon la méthode du cadrat. Pour Saint-Trojan, l’estimation obtenue représente 88,7 tonnes (± 67, 3) pour 14,56 millions (± 11,23) d’individus. A Bellevue, le stock de palourdes est estimé à 150,7 tonnes (± 114,9) pour 39,42 millions (± 28,66) d’individus. Les palourdes de taille commerciale représentent respectivement 18,2 et 53,8 tonnes. Avec une densité de palourdes commerciales de 0,76 t/ha, Bellevue s’avère être mieux dotée qu’Arcachon et Saint-Trojan (0,23 t/ha), mais moins bien que la rivière de Pont l’Abbé et le Golfe du Morbihan. La structure en âge des populations a pu être établie grâce à l’analyse des histogrammes de fréquence des tailles avec le logiciel FISAT II. Le stock de palourdes de Bellevue lui confère un intérêt pour la pêche à pied professionnelle alors qu’à Saint-Trojan, la faiblesse du stock indiquerait une mauvaise gestion de la ressourc

Does Encapsulation Protect Embryos from the Effects of Ocean Acidification? The Example of Crepidula fornicata

International audienceEarly life history stages of marine organisms are generally thought to be more sensitive to environmental stress than adults. Although most marine invertebrates are broadcast spawners, some species are brooders and/or protect their embryos in egg or capsules. Brooding and encapsulation strategies are typically assumed to confer greater safety and protection to embryos, although little is known about the physico-chemical conditions within egg capsules. In the context of ocean acidification, the protective role of encapsulation remains to be investigated. To address this issue, we conducted experiments on the gastropod Crepidula fornicata. This species broods its embryos within capsules located under the female and veliger larvae are released directly into the water column. C. fornicata adults were reared at the current level of CO2 partial pressure (pCO2) (390 μatm) and at elevated levels (750 and 1400 μatm) before and after fertilization and until larval release, such that larval development occurred entirely at a given pCO2. The pCO2 effects on shell morphology, the frequency of abnormalities and mineralization level were investigated on released larvae. Shell length decreased by 6% and shell surface area by 11% at elevated pCO2 (1400 μatm). The percentage of abnormalities was 1.5- to 4-fold higher at 750 μatm and 1400 μatm pCO2, respectively, than at 390 μatm. The intensity of birefringence, used as a proxy for the mineralization level of the larval shell, also decreased with increasing pCO2. These negative results are likely explained by increased intracapsular acidosis due to elevated pCO2 in extracapsular seawater. The encapsulation of C. fornicata embryos did not protect them against the deleterious effects of a predicted pCO2 increase. Nevertheless, C. fornicata larvae seemed less affected than other mollusk species. Further studies are needed to identify the critical points of the life cycle in this species in light of future ocean acidification

Better off alone? New insights in the symbiotic relationship between the flatworm Symsagittifera roscoffensis and the microalgae Tetraselmis convolutae

International audienceThe acoel flatworm Symsagittifera roscoffensis lives in obligatory symbiosis with the microalgal chlorophyte Tetraselmis convolutae. Although this interaction has been studied for more than a century, little is known on the potential reciprocal benefits of both partners, a subject that is still controversial. In order to provide new insights into this question, we have compared the photophysiology of the free-living microalgae to the symbiotic form in the flatworm, both acclimated at different light irradiances. Photosynthesis – Irradiance curves showed that the free-living T. convolutae had greater photosynthetic performance (i.e., oxygen production rates, ability to harvest light) than their symbiotic form, regardless of the light acclimation. However, they were affected by photoinhibition under high irradiances, which did not happen for the symbiotic form. The resistance of symbiotic microalgae to photoinhibition were corroborated by pigment analyses, which evidenced the induction of photoprotective mechanisms such as xanthophyll cycle as well as lutein and β-carotene accumulation. These processes were induced even under low light acclimation and exacerbated upon high light acclimation, suggesting a global stress situation for the symbiotic microalgae. We hypothesize that the internal conditions in the sub-epidermal zone of the flatworm (e.g., osmotic and pH), as well as the phototaxis toward high light imposed by the worm in its environment, would be major reasons for this chronic stress situation. Overall, our study suggests that the relationship between S. roscoffensis and T. convolutae may be a farming strategy in favor of the flatworm rather than a symbiosis with mutual benefits

Trophic structure of two intertidal Fucus spp. communities along a vertical gradient: Similarity and seasonal stability evidenced with δ^13C and δ^15N

International audienceIntertidal communities dominated by canopy-forming macroalgae typically exhibit some differences in their specific composition that are related to their location along the emersion gradient of rocky shores. Tidal level is also expected to affect resource availability for both primary producers and consumers, potentially leading to divergence in the trophic structure of these communities. Furthermore, in temperate areas, the alternation of seasons has usually a large influence on the primary production and on life-history traits of numerous species, which may induce some changes in the food webs of intertidal communities. Thus, this study aimed to investigate the trophic structure of two intertidal communities located at different tidal levels, over several seasons. Focusing on the dominant species of primary producers and consumers, the food webs of the Fucus vesiculosus Linnaeus and Fucus serratus Linnaeus communities were studied during four successive seasons, using an isotopic (δ13C and δ15N) approach. Due to the diversity of primary producers and consumers living in these two communities, food webs were relatively complex and composed of several trophic pathways. These food webs remained rather conserved over the successive seasons, even though some variability in isotopic signature and in diet has been highlighted for several species. Finally, despite their location at different tidal levels, the two Fucus spp. communities exhibited nearly the same trophic structure, with common consumer species displaying similar isotopic signature in both of them