Fonctionnalités écologiques, transformations et gestion des habitats de l'Infralittoral rocheux en Méditerranée Nord-occidentale: le cas des nourriceries de poissons (Téléostéens).

The aim of this PhD was to better understand the characteristics and consequences of the transformations of Mediterraneaninfralittoral fish (Teleostei) nursery habitats, in order to gather useful knowledge for management of coastal areas inMediterranean regions. Among the seascape mosaic, Cystoseira forests, a threatened macrophytes-formed habitat, displayedhigher densities of fish juveniles (notably Labridae and Serranidae) than alternate states of rocky bottoms photophilicbiocenosis, namely Dictyotales and Sphacelariales bushland and barren grounds. The relatively higher nursery value ofCystoseira forests (for Symphodus spp.) and of the shallow heterogeneous blocks and pebbles gentle slopes (for Diplodus spp.) where consistent through space at both local (1 km) and regional (20 km) scales, although juvenile densities varied significantly in space between sites for a given nursery habitat. The spatial variability of juvenile densities, both across various habitats and among Cystoseira forests was notably related to habitat tri-dimensional structure (heterogeneity and complexity); this structure provided refuges for juveniles and influenced namely predation success of their predators. This experimental and observational study demonstrated that habitat human-induced transformations, such as forest fragmentation and cover density decrease critically reduced their nursery value for coastal fishes. Our results suggest that the fish productivity virtually lost in areas where forests have already disappeared may be considerable. Finally, these essential habitats were scarce and not homogenously distributed along the coast: in the case of Diplodus spp., less than 10% of the studied rocky shores displayed nursery habitats. Furthermore, the present work highlighted that the current design of management measures did not take into account the spatial distribution of these nursery habitats and the connectivity between all essential habitats at each life stages. A conceptual scheme aiming at adopting such “seascape approach” is proposed, in order to better target conservation efforts and guarantee coastal fish assemblages’ replenishment.Cette thèse avait pour objet les habitats de l’Infralittoral rocheux Méditerranéen qui ont un rôle de nourricerie pour les juvénilesde poissons (Téléostéens). Cette étude visait à mieux comprendre leurs caractéristiques et les conséquences de leurstransformations, notamment d’origine anthropique, dans le but de rassembler des données utiles à la gestion des zonescôtières. Au sein de la mosaïque paysagère sous-marine, parmi les faciès de la biocénose des macrophytes photophiles de laroche infralittorale, les forêts de Cystoseires forment un habitat à macrophytes arborescentes qui est menacé. Cette thèse adémontré que ces forêts abritaient des densités plus élevées de juvéniles de poissons (notamment Labridae et Serranidae) quecelles observées au sein de faciès alternatifs, en particulier les brousses à Dictyotales et Sphacelariales et les faciès desurpâturage. La haute valeur relative de nourricerie, que ce soit des forêts de Cystoseires (pour trois espèces du genreSymphodus), ou des petits fonds à blocs et galets (pour les espèces du genre Diplodus), a été observée de manière récurrentedans les différents sites littoraux étudiés aussi bien à l’échelle locale (1 km) que régionale (20 à 100 km). Cependant, pour unhabitat donné, les densités de juvéniles ont montré une forte variabilité spatiale entre sites. La variabilité spatiale des densitésde juvéniles, aussi bien entres sites des forêts à Cystoseires que d’un habitat à l’autre, était notamment associée aux différencesde structure tridimensionnelle de l’habitat (hétérogénéité et complexité). Cette structuration fournissait un refuge pour lesjuvéniles et a en particulier influencé l’efficacité de leurs prédateurs. Ces travaux, sur la base de manipulations expérimentaleset d’observations in situ, ont démontré que les transformations des habitats, telles que la fragmentation des forêts ou ladiminution de la densité de leur couverture, réduisaient drastiquement leurs valeurs de nourricerie pour les poissons côtiers.Ces résultats suggèrent que la productivité en poissons virtuellement perdue, dans les zones où les forêts ont déjà totalementdisparu, est considérable. Par ailleurs, ces habitats essentiels se sont avérés rares et in-équitablement distribués le long descôtes : dans le cas des Diplodus spp., moins de 10% des côtes rocheuses étudiées présentaient des habitats nourriceries. Enfin,ce travail a mis en évidence que la planification actuelle des mesures de gestion des zones côtières méditerranéennes ne prenaitgénéralement pas en compte la distribution spatiale des habitats nourriceries, ni leur connectivité avec les autres habitatsessentiels à chaque étape clef du cycle de vie des poissons. Un schéma conceptuel, visant à adopter une telle « approchepaysage » de la gestion, est proposé : il vise à promouvoir une focalisation optimale des efforts de conservation et à garantirainsi le renouvellement des peuplements de poissons côtiers

Effect of depth and canopy height on the nursery value of Cystoseira balearica forests for Mediterranean rocky reef fishes

We studied effects of depth and Cystoseira balearica forests canopy height on coastal juvenile fish assemblages of Minorca Island. Results showed a clear differentiation of juvenile fish assemblages due to depth: assemblage in the shallowest range (3-4m) was characterized by higher densities of Thalassoma pavo, deeper ones (6-8, 10-12 m) by higher densities of Coris julis. Smallest juveniles of both species were more abundant within forests displaying the highest canopy height; meanwhile largest juveniles were more abundant within low Cystoseira forests. Also, both species showed predominantly a cryptic behavior on forest of higher canopy height, and a temporal one when canopy was lower. This study supports the importance of preserving healthy Cystoseira forests in order to preserve their nursery value for these two Labrid species0,000

Occurrence of the Atlantic species, Pisodonophis semicinctus (Osteichthyes: Ophichthidae), along the Mediterranean coast

Short communicatio

The Three-Dimensional Structure of Mediterranean Shallow Rocky Reefs: Use of Photogrammetry-Based Descriptors to Assess Its Influence on Associated Teleost Assemblages

International audienceIn the Mediterranean Sea, shallow rocky reefs and the associated three-dimensional (3D) structure support rich and abundant communities; they are therefore of functional importance, in particular for the renewal of fish stocks. However, these habitats and their functions are likely to be altered by anthropogenic pressures inducing habitat transformations. It is therefore necessary to assess their 3D structure, their transformations and relationship to communities, especially for management and conservation purposes. In this article we aimed (i) to compare two methods that quantify the metrics of the 3D structure (rugosity) of shallow rocky reefs (chain-and-tape method and photogrammetry), and (ii) to quantify the possible links between this habitat structure and the fish assemblages. We found that photogrammetry and the chain-and-tape method yielded a similar estimate of rugosity, but photogrammetry was the most efficient method in terms of measurement quality and time (when considering in-water acquisition). This method also displayed the best repeatability. The 3D habitat descriptors (mean surface rugosity, variation of surface rugosity, and depth) differed significantly between the studied sites and were therefore included as covariables. Total fish abundance and species richness increased with higher mean surface rugosity. In addition, the composition of fish assemblages was significantly influenced by surface rugosity, although this effect was modulated by depth. When focusing on specific taxa, neither density patterns nor size class distributions displayed clear patterns in relation to rugosity metrics. However, this study demonstrated that spatial variability of teleost fish assemblages can be explained by habitat rugosity which probably increases the number of shelters and food resources, and therefore improves chances of survival. In addition, our study has shown that photogrammetry is an appropriate method to assess 3D structure metrics in a temperate rocky reef

The three-dimensional structure of Cymodocea nodosa meadows shapes juvenile fish assemblages (Fornells Bay, Minorca Island)

International audienceThe role of the meadows of the Mediterranean seagrass Cymodocea nodosa as nursery habitats for fish remains largely unknown and there are only few studies investigating the influence of their structure on juvenile assemblages. Here, we monitored juvenile fish assemblages among shallow Cymodocea nodosa meadows (0–1 m) in Minorca Island (north-western Mediterranean Sea) in both July and September 2013. To assess the influence of structural components on juvenile fish assemblages, we selected two different meadow structure types: heterogeneous with intermingled boulders and homogeneous meadows, i.e. without boulders. Juvenile fish assemblages varied significantly among these two meadow structures. Heterogeneous meadows had higher total juvenile density and species richness, where some species were only found in these portions, such as Coris julis and Serranus spp. Other species, such as Symphodus spp. and Sarpa salpa, were also more abundant within heterogeneous meadows. However, densities of some species were not increased in heterogeneous meadows demonstrating a specific response to habitat structure. For instance, Diplodus annularis displayed similar abundances in both heterogeneous and homogeneous portions of the meadow. Our study reveals that the intrinsic structural variability of seagrass meadows plays a key role for the assemblage of several fish species that are characterized by different early life history strategies

Adaptive Vertical Positioning as Anti-Predator Behavior: The Case of a Prey Fish Cohabiting with Multiple Predatory Fish within Temperate Marine Algal Forests

Prey fish cohabit with specialized predator fish within structurally complex habitats. How the vertical stratification of the habitat affects lethal and behavioral predator–prey interactions and contributes to explaining these patterns has never been investigated within a forest-like marine habitat, i.e., a habitat containing three vertical strata (understory, canopy, open-water above). We studied this in tank experiments, with a model prey (the wrasse Symphodus ocellatus) and two model predators (the stalk-and-attack comber Serranus cabrilla and the sit-and-wait scorpionfish Scorpaena porcus), which are among the most abundant prey and predators cohabiting in Mediterranean Cystoseira forests. Wrasse anti-predator behavior was predator-specific. When exposed to the scorpionfish, the wrasse increased its vertical distance from the predator, regardless of the habitat structure. Conversely, when exposed to the comber, the wrasse sought refuge within forest structures: (1) the canopy provides more hiding opportunities due to its high complexity, and (2) the understory provides more escape/avoidance opportunities due to (a) its low complexity that allows for fast prey movements, and (b) the presence of the canopy above that limits the comber’s access to the understory. Our results suggest that habitat vertical stratification mediates predator–prey interactions and potentially promotes the co-existence of prey and multiple predators within marine forests

Investigating the outcomes of a threatened gorgonian in situ transplantation: Survival and microbiome diversity in Paramuricea clavata (Risso, 1827)

International audienc

3D Photogrammetry Modeling Highlights Efficient Reserve Effect Apparition After 5 Years and Stillness After 40 for Red Coral (Corallium rubrum) Conservation in French MPAs

International audienceImaging the marine environment is more and more useful to understand relationships between species, as well as natural processes. Developing photogrammetry allowed the use of 3D measuring to study populations dynamics of sessile organisms at various scales: from colony to population. This study focuses on red coral (Corallium rubrum) , as known as precious coral. Metrics measured at a colony scale (e.g., maximum height, diameter and number of branches) allowed population understanding and a comparison between an old (Cerbère-Banyuls reserve) vs. a new (Calanques National Park) MPA. Our results suggested a 5-year time step allows the appearance of a significant difference between populations inside vs. outside the Calanques National Park no-take zones. Red coral colonies were taller and had more branches inside no-take zones. A significant difference was still observable for the populations inside the Cerbère-Banyuls reserve after 40 years of protection, reflecting the sustainability and effectiveness of precautionary measures set by the reserve. The impacts at the local level (mechanical destruction) and those presumed to occur via global change (climatic variations) underline the need to develop strategies both to follow the evolutions of red coral populations but also to understand their resilience. Photogrammetry induced modeling is a time and cost effective as well as non-invasive method which could be used to understand population dynamics at a seascape scale on coralligenous reefs

Location and geomorphological characteristics of the sampled coves and sampling characteristics.

<p>S: Sediment (CS Coarse Sand, MS Medium Sand); W: Width (m); L: Length (m); SL: Shoreline Length (m); A: Area (m²); NSD: Number of sampling days; ET: number of effective transects; TN: total number of white seabream juveniles censed during the study period; MNJ: maximum juveniles observed per day; TL: size ranges considering the Total Length (mm).</p

Study sites.

<p>The two distinct sampling locations at the Northeast (NE) and Southwest (SW) of the Menorca Island and the six coves monitored during the study. The Acoustic Doppler Current Profiler (ADCP) localization and the current variation ellipses measured at different depths (darker is shallower) are also indicated at the SW site. Maps were created by the authors by merging topographical maps generated with ArgGIS using IDEIB terrain elevation model (<a href="http://ideib.caib.es/visualitzador/visor.jsp" target="_blank">http://ideib.caib.es/visualitzador/visor.jsp</a>) and the MATLAB software. There are no copyright restrictions associated and permissions for publication are not necessary.</p