Successful aquacultural production of juvenile fish requires that the optimal rearing conditions be applied. However, for many fish species, there is a significant knowledge gap concerning these conditions. In this study, we evaluated the effects of stocking density on the survival and growth of brown meagre, Sciaena umbra (L.), during rearing trials in an experimental hatchery. This research forms part of a feasibility project to improve the aquacultural production of brown meagre. Four initial larval density treatments (5, 10, 30, and 70 larvae per L) were established. At 0, 9, 17, 22, and 25 days post-hatching, we measured the total length, coefficient of variation in length, and specific growth rate. The physicochemical water parameters remained at satisfactory levels for fish culture throughout the experiment. Lower densities promoted better growth in terms of total length, specific growth rate, and survival. We observed a significant negative correlation between larval density and length growth/survival. Thus, the low larval density treatment yielded the highest survival (48.5% ± 3.46%), growth in final total length (11.9 ± 1.09 mm), and specific growth rate (5.13% ± 0.39% per day). Increased stocking density therefore negatively affects growth and survival, reduces homogeneity, but increases the production of S. umbra larvae. This study helps identify optimal aquaculture conditions for maximizing the production of juvenile S. umbra for ecological restoration.

An extensive survey of macroparasites in 320 European eel Anguilla anguilla (Linnaeus, 1758) was conducted in two brackish lagoons and eleven freshwater localities in the Mediterranean island of Corsica (France) between spring 2021 and winter 2021–2022. It resulted in the identification of nineteen parasites: two Monogea, four Digenea, one Copepoda, four Acanthocephala, three Cestoda, and five Nematoda, including the first geographical records, as Corsican freshwater sites were studied for the first time. The silvering stage was determined, and the eels were aged through otolithometry to compare parasite communities. Classic parasitology indices, a multivariate analysis, and an analysis of indicator values (IndVal) showed clear preferences towards the host’s habitat and salinity. Seasonal variations were shown for several parasites. A dataset from the same two coastal lagoons was used to study the changes in the parasite communities over the last decade, and this showed an increase in the prevalence and abundance of three invasive helminth species: the Monogenea Pseudodactylogyrus bini (Kikuchi, 1929), Pseudodactylogyrus anguillae (Yin and Sproston, 1948) Gusev, 1965 and the Nematoda Anguillicola crassus Kuwahara, Niimi, and Itagaki, 1974. These pathogenic parasites were found in all sampled localities, except for the two Monogenea in the polyhaline-to-euhaline Urbino lagoon. It is thus advised that future management measures take into account the environmental preferences of the most concerning parasites.

Small and medium-sized islands (SMI) combine high ecological value with limited resources and vulnerability to climatic and environmental risks. Nature-based solutions (NbS) can contribute to addressing some of these challenges, but studies on the uptake and effectiveness of NbS in SMI remain scattered, with few systematic syntheses. Here, we introduce the SMI-NbS compendium, a comprehensive and open-access dataset compiling 280 NbS case studies implemented across SMI worldwide, developed through a systematic review of published and grey literature. Each SMI-NbS case study includes information on the location, NbS category, ecosystem types, societal challenges addressed, associated co-benefits, and links to the United Nations’ Sustainable Development Goals (SDGs). The SMI-NbS compendium provides practical information on NbS implementation and identifies current research trends and gaps, such as the dominance of ecological and climate-focused NbS, with limited integration of other socio-economic challenges, thereby supporting further research and enabling knowledge exchange across the science-policy-practice interface to inform sustainable development pathways in SMI.

The demand for the purple sea urchin Paracentrotus lividus has led to the decline of its wild populations, increasing interest in cultivating this species for commercial purposes and ecological restoration purposes. Consequently, there is a need to expand knowledge about the optimal conditions for sea urchin aquaculture, particularly regarding food regimes. Here, we evaluate the effects of several vegetable diets on the survival and growth of early juveniles of P. lividus. Using an outdoor experimental assay, we fed early juveniles (5–6.5 mm) various diets: fresh algae (Ulva sp.), aquaculture pellets, and vegetables (carrot, spinach, and maize) presented as individual or mixed diets (equal mass proportions). All diets were provided ad libitum in equal mass proportions. After 120 days, the pellet‐fed urchins showed good growth but a high mortality rate (>40%). The Ulva sp. diet, considered the control regime mimicking wild sea urchin diet, resulted in low mortality but poor growth performance (maximum of 10.92 ± 1.94 mm in diameter and 0.68 ± 0.26 g in weight). In contrast, plant‐based diets, especially those containing maize, led to the highest growth and lowest mortality rates (<5%). Notably, the triple mixed diet (carrot–spinach–maize) resulted in a threefold size increase, as the P. lividus juveniles reached 15 mm in 4 months. This study demonstrates the effectiveness of inexpensive, ready‐to‐use vegetable‐based diets in optimizing rearing protocols for early juveniles of P. lividus. It offers preliminary insights into dietary preferences to rapidly attain an adequate release size for purple urchin aimed at restocking wild populations and balancing aquaculture and ecological restoration needs.

The Mediterranean spider crab, Maja squinado (Herbst, 1788), is one of the largest species of spider crab and holds significant interest for commercial and stock enhancement purposes. Thus, it is essential to identify optimal rearing conditions to attempt mass production, as several factors affect the growth and survival of this species during the early juvenile phase in aquaculture. In this study, we evaluated the effect of stocking density on the growth parameters and survival rate of M. squinado reared in an experimental hatchery as part of a spider crab stock enhancement feasibility project. Groups of spider crabs were reared at two initial densities (1.6 and 4.6 individuals·L⁻¹). After 29 days of culture (i.e., from megalopae to C3 juveniles), early juveniles reared at the higher density showed a significantly higher weight gain ratio and specific growth rate as well as a significantly higher Fulton’s condition index specifically for C3 juveniles, reflecting a better general well-being. In contrast, the survival at the higher density was negatively affected compared to the lower rearing density. This study improves baseline knowledge about M. squinado rearing to help develop commercial applications and establish management strategies and restoration programs for endangered M. squinado populations going forward.

Une étude parasitaire de l'anguille d'Europe a été menée dans les lagunes de Biguglia et d'Urbino en Corse. La composition des communautés de parasites a été décrite. Treize espèces parasites ont été identifiées parmi lesquelles: trois digènes, Bucephalus anguillae, Deropristis inflata, Lecithochirium musculus; un monogène, Pseudodactylogyrus anguillae; trois cestodes, Bothriocephalus claviceps, Proteocephalus macrocephalus, Myzophyllobothrium sp. (larve); trois nématodes, Anguillicoloides crassus, Contracaecum sp. (larve enkystée), Goezia anguillae; un acanthocéphale, Acanthocephaloides incrassatus; un copépode, Ergasilus gibbus; et un myxozoaire, Myxobolus portucalensis. La présence d'espèces invasives, notamment le parasite branchial P. anguillae et le nématode parasite A. crassus, dans les lagunes corses est confirmée. Ces espèces, et particulièrement le monogène, présentent des valeurs épidémiologiques croissantes depuis les dernières études menées. Plusieurs espèces présentent des différences de prévalence significatives entre les deux lagunes. Des différences au niveau de la richesse spécifique et des valeurs de diversité, plus élevées pour les parasites des anguilles de la lagune d'Urbino au niveau intestinal métacommunautaire et infracommunautaire, ont été démontrées. Cependant les valeurs les plus élevées de diversité spécifique et les valeurs de dominance les plus basses ont été calculées pour les communautés parasitaires des anguilles de la lagune de Biguglia. Nous avons également mis en avant une diversité parasitaire spécifique plutôt faible chez les anguilles des lagunes corses par rapport aux autres lagunes d'Europe. Les communautés parasitaires de l'anguille d'Europe dans les lagunes de Biguglia et d'Urbino en Corse sont marquées par l'environnement de leur hôte. Une dépendance vis-à-vis de la salinité de la lagune a ainsi été démontrée. Les valeurs d'infestation les plus élevées ont été observées durant les saisons les plus chaudes de l'année pour la majorité des espèces parasites observées (B. anguillae, D. inflata, L. musculus, P. anguillae, P. macrocephalus, A. crassus, les kystes de Contracaecum sp., A. incrassatus et E. gibbus). Nous avons également démontré que l'état d'argenture et la taille ont une influence significative sur les taux d'infestation de sept espèces parasites (D. inflata, L. musculus, P. anguillae, P. macrocephalus, les kystes de Contracaecum sp., A. incrassatus et E. gibbus). La méthode de l'espèce indicatrice a confirmé que le site d'étude, la saison, l'état d'argenture ou la taille de l'anguille pouvait influer sur la présence de certaines espèces parasites. Le tégument de trois digènes parasites de l'anguille d'Europe, B. anguillae, L. musculus et D. inflata, a été étudié en microscopie électronique à balayage et à transmission. Nous avons démontré la présence de structures caractéristiques de l'organisation tégumentaire des digènes ainsi que de formations spécifiques, notamment au niveau de la structure des récepteurs sensoriels et des écailles.