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Abstract Background The measurement of the energy available for growth (scope of growth, SFG) can be used in bivalves to make a long-term prediction in a short-term experiment of the condition of the individual. In order to tackle the best conditions for captive maintenance of Mediterranean Pinnids, a SFG study was conducted using Pinna rudis as a model species. Three diets were examined to test the viability of live microalgae and commercial products: i) a control diet using 100% of live microalgae based on the species Isochrysis galbana (t-ISO), ii) a 100% of commercial microalgae diet based on the product Shellfish Diet 1800®, and iii) a 50/50% mix diet of I. galbana (t-ISO) and Shellfish Diet 1800®. Results SFG results showed significant differences among diets in the physiological functions measured and suggested lower acceptability and digestibility of the commercial product. Negative SFG values were obtained for the commercial diet which indicates that it should be rejected for both Pinnid maintenance. The mixed diet showed improved physiological performance compared to the commercial diet, resulting in a higher SFG that had no significant differences with the control diet. However, in the long-term, the lower digestibility of the mixed diet compared to the control diet could lead to a deterioration of individuals’ conditions and should be considered cautiously. Conclusions This work represents the first case study of SFG in Pinna spp. and provides fundamental data on dietary needs for the critically endangered species, P. nobilis.

Knowledge of the genetic structure and dispersal patterns for keystone and vulnerable species is essential to the establishment of conservation strategies. Since autumn 2016, the Critically Endangered Pinna nobilis bivalve has suffered mass mortality events throughout the Mediterranean Sea, causing mortality of up to 100% in affected populations. To propose appropriate reintroduction programs for its recovery, the present study sought to determine the genetic structure and local dispersal patterns from a well-documented population of P. nobilis. Using 19 microsatellite markers, we obtained genotypic information for 771 individuals from 9 localities within Cabrera National Park (CNP). The CNP population of P. nobilis was a single and homogeneous population, with nearly half of the sampled individuals being related through 333 half-sib and 14 full-sib relationships. The siblings belonged to 126 different family clusters composed of 2-8 individuals recruited during several recruitment events from up to 4 different localities. No evidence was found to suggest that the population was self-sustaining, since no parent-offspring dyad was found. However, the fine-scale dispersal patterns observed in Santa Maria Bay highlight the importance of this locality for the sustainment of the population as a whole. These findings suggest that the CNP could be a good choice for future reintroduction programs. Future studies that compile data from this and other studies conducted in CNP should be considered when modeling for reintroduction.

The Pinna nobilis , a Mediterranean mollusc, has suffered population declines due to a massive mortality event associated with various factors including the parasite Haplosporidium pinnae . Some populations show resilience, possibly due to local environmental conditions. In this study, a molecular multiplex PCR method was developed using species-specific primers targeting Internal Transcribed Spacer (ITS) regions of P. nobilis and P. rudis , allowing accurate species identification and hybrid detection. Samples from Mediterranean areas were analysed, including putative hybrids and individuals from five other bivalve species. DNA was isolated, ITS regions were amplified and sequenced, and phylogenetic analyses confirmed species differentiation and primer specificity. The multiplex-PCR successfully identified P. nobilis , P. rudis , and their hybrids based on distinct amplicon patterns. This study highlights the value of molecular tools in species conservation, especially for monitoring and managing hybridization, supporting effective biodiversity conservation strategies., Competing Interests: The authors declare no conflict of interest., (© 2024 The Author(s). Ecology and Evolution published by John Wiley & Sons Ltd.)

The critically endangered endemic bivalve Pinna nobilis from the Mediterranean Sea suffered a sudden population decline after a mass mortality event in early autumn 2016. Conservation efforts aimed at preventing extinction included safeguarding resistant individuals and implementing a breeding plan to contribute to the repopulation of the species. This study utilized a model combining Lagrangian dispersion and connectivity analyses to pinpoint optimal restocking sites in the Western Mediterranean. Our approach allowed to identify locations capable of sustaining and generating larvae for broader repopulation in key areas of the Western Mediterranean Sea prior to the mass mortality event. Six important repopulation locations from Murcia, Valencia and Balearic Islands were selected for reintroduction efforts. The results obtained in this study show how the network could be self-sufficient and able to self-replenish itself of recruits. Overall, our work can be used to direct the reintroduction of resistant animals in the Western Mediterranean Sea., (Copyright © 2024 The Authors. Published by Elsevier Ltd.. All rights reserved.)

The fan mussel Pinna nobilis is currently on the brink of extinction due to a multifactorial disease mainly caused to the highly pathogenic parasite Haplosporidium pinnae , meaning that the selection pressure outweighs the adaptive potential of the species. Hopefully, rare individuals have been observed somehow resistant to the parasite, stretching the need to identify the traits underlying this better fitness. Among the candidate to explore at first intention are fast-evolving immune genes, of which toll-like receptor (TLR). In this study, we examined the genetic diversity at 14 TLR loci across P. nobilis , Pinna rudis and P. nobilis  ×  P. rudis hybrid genomes, collected at four physically distant regions, that were found to be either resistant or sensitive to the parasite H. pinnae . We report a high genetic diversity, mainly observed at cell surface TLRs compared with that of endosomal TLRs. However, the endosomal TLR-7 exhibited unexpected level of diversity and haplotype phylogeny. The lack of population structure, associated with a high genetic diversity and elevated dN/dS ratio, was interpreted as balancing selection, though both directional and purifying selection were detected. Interestingly, roughly 40% of the P. nobilis identified as resistant to H. pinnae were introgressed with P. rudis TLR. Specifically, they all carried a TLR-7 of P. rudis origin, whereas sensitive P. nobilis were not introgressed, at least at TLR loci. Small contributions of TLR-6 and TLR-4 single-nucleotide polymorphisms to the clustering of resistant and susceptible individuals could be detected, but their specific role in resistance remains highly speculative. This study provides new information on the diversity of TLR genes within the P. nobilis species after MME and additional insights into adaptation to H. pinnae that should contribute to the conservation of this Mediterranean endemic species., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (© 2023 The Authors. Ecology and Evolution published by John Wiley & Sons Ltd.)

In this study, we investigated the presence of the parasite Haplosporidium pinnae , which is a pathogen for the bivalve Pinna nobilis , in water samples from different environments. Fifteen mantle samples of P. nobilis infected by H. pinnae were used to characterize the ribosomal unit of this parasite. The obtained sequences were employed to develop a method for eDNA detection of H. pinnae . We collected 56 water samples (from aquaria, open sea and sanctuaries) for testing the methodology. In this work, we developed three different PCRs generating amplicons of different lengths to determine the level of degradation of the DNA, since the status of H. pinnae in water and, therefore, its infectious capacity are unknown. The results showed the ability of the method to detect H. pinnae in sea waters from different areas persistent in the environment but with different degrees of DNA fragmentation. This developed method offers a new tool for preventive analysis for monitoring areas and to better understand the life cycle and the spread of this parasite.

Climate change is causing an increase in the frequency and intensity of marine heatwaves (MHWs) and mass mortality events (MMEs) of marine organisms are one of their main ecological impacts. Here, we show that during the 2015-2019 period, the Mediterranean Sea has experienced exceptional thermal conditions resulting in the onset of five consecutive years of widespread MMEs across the basin. These MMEs affected thousands of kilometers of coastline from the surface to 45 m, across a range of marine habitats and taxa (50 taxa across 8 phyla). Significant relationships were found between the incidence of MMEs and the heat exposure associated with MHWs observed both at the surface and across depths. Our findings reveal that the Mediterranean Sea is experiencing an acceleration of the ecological impacts of MHWs which poses an unprecedented threat to its ecosystems' health and functioning. Overall, we show that increasing the resolution of empirical observation is critical to enhancing our ability to more effectively understand and manage the consequences of climate change., (© 2022 The Authors. Global Change Biology published by John Wiley & Sons Ltd.)

Background: The measurement of the energy available for growth (scope of growth, SFG) can be used in bivalves to make a long-term prediction in a short-term experiment of the condition of the individual. In order to tackle the best conditions for captive maintenance of Mediterranean Pinnids, a SFG study was conducted using Pinna rudis as a model species. Three diets were examined to test the viability of live microalgae and commercial products: i) a control diet using 100% of live microalgae based on the species Isochrysis galbana (t-ISO), ii) a 100% of commercial microalgae diet based on the product Shellfish Diet 1800®, and iii) a 50/50% mix diet of I. galbana (t-ISO) and Shellfish Diet 1800®., Results: SFG results showed significant differences among diets in the physiological functions measured and suggested lower acceptability and digestibility of the commercial product. Negative SFG values were obtained for the commercial diet which indicates that it should be rejected for both Pinnid maintenance. The mixed diet showed improved physiological performance compared to the commercial diet, resulting in a higher SFG that had no significant differences with the control diet. However, in the long-term, the lower digestibility of the mixed diet compared to the control diet could lead to a deterioration of individuals' conditions and should be considered cautiously., Conclusions: This work represents the first case study of SFG in Pinna spp. and provides fundamental data on dietary needs for the critically endangered species, P. nobilis., (© 2022. The Author(s).)

Recently, Pinna nobilis pen shells population in Mediterranean Sea has plummeted due to a Mass Mortality Event caused by an haplosporidian parasite. In consequence, this bivalve species has been included in the IUCN Red List as "Critically Endangered". In the current scenario, several works are in progress to protect P. nobilis from extinction, being identification of hybrids (P. nobilis x P. rudis) among survivors extremely important for the conservation of the species.Morphological characteristics and molecular analyses were used to identify putative hybrids. A total of 10 individuals of each species (P. nobilis and P. rudis) and 3 doubtful individuals were considered in this study. The putative hybrids showed shell morphology and mantle coloration intermingled exhibiting both P. nobilis and P. rudis traits. Moreover, the analyses of 1150 bp of the 28S gene showed 9 diagnostic sites between P. rudis and P. nobilis, whereas hybrids showed both parental diagnostic alleles at the diagnostic loci. Regarding the multilocus genotypes from the 8 microsatellite markers, the segregation of two Pinna species was clearly detected on the PCoA plot and the 3 hybrids showed intermediate positions.This is the first study evidencing the existence of hybrids P. nobilis x P. rudis, providing molecular methodology for a proper identification of new hybrids. Further studies testing systematically all parasite-resisting isolated P. nobilis should be undertaken to determine if the resistance is resulting from introgression of P. rudis into P. nobilis genome and identifying aspects related to resistance.

The present work, which is the first comparative study of the growth of the fan mussel Pinna nobilis in the western Mediterranean, encompasses 12 populations of this species living in different environments in France and Spain. Two hundred nine shells were processed and used to obtain growth records from the posterior adductor muscle scar. Size-at-age data were fitted to the Von Bertalanffy growth model. Considerable variability in growth parameters and age was detected among the populations. The results show that the only two fan mussel populations remaining in Spain, which live in an estuary and a coastal lagoon, occupy habitats that are optimal for fast growth, but individuals show low longevity, complicating the long-term conservation of the species. Multivariate analyses groups the populations into three groups (SO, EO and LG), and a general model is proposed for each group; the model can be used as an approximation to calculate the ages of individuals living in similar environments., (Copyright © 2019. Published by Elsevier Ltd.)

A mass mortality event is devastating the populations of the endemic bivalve Pinna nobilis in the Mediterranean Sea from early autumn 2016. A newly described Haplosporidian endoparasite (Haplosporidium pinnae) is the most probable cause of this ecological catastrophe placing one of the largest bivalves of the world on the brink of extinction. As a pivotal step towards Pinna nobilis conservation, this contribution combines scientists and citizens' data to address the fast- and vast-dispersion and prevalence outbreaks of the pathogen. Therefore, the potential role of currents on parasite expansion was addressed by means of drift simulations of virtual particles in a high-resolution regional currents model. A generalized additive model was implemented to test if environmental factors could modulate the infection of Pinna nobilis populations. The results strongly suggest that the parasite has probably dispersed regionally by surface currents, and that the disease expression seems to be closely related to temperatures above 13.5 °C and to a salinity range between 36.5-39.7 psu. The most likely spread of the disease along the Mediterranean basin associated with scattered survival spots and very few survivors (potentially resistant individuals), point to a challenging scenario for conservation of the emblematic Pinna nobilis, which will require fast and strategic management measures and should make use of the essential role citizen science projects can play.

This study provides morphological and molecular characterization of a new species, Haplosporidium pinnae), very likely responsible for mass mortality of fan mussels, Pinna nobilis, in the Western Mediterranean Sea. The parasite was found in dead or moribund P. nobilis but did not occur in healthy fan mussels from locations that were not affected by abnormal mortality. Histological examination of infected fan mussels showed uninucleate cells of a haplosporidan parasite throughout the connective tissue and hemolymph sinuses of the visceral mass and binucleate cells and, rarely, multinucleate plasmodia were also detected in the connective tissue. Additionally, stages of sporulation occurred in the epithelium of the host digestive gland tubules. Spores were slightly ellipsoidal with a hinged operculum in one pole. Typical haplosporosomes were not found with TEM but vesicles with two concentric membranes resembling haplosporosomes were abundant in the cytoplasm of the multinucleate plasmodia occurring in host digestive gland tubules. SEM analysis showed multiple structures on the spore surface; some spores had two or four long tape-like filaments attached to the spore wall. Phylogenetic analysis based on the SSU rDNA sequence placed this parasite within a large clade including species of the order Haplosporida, not in the Bonamia/Minchinia subclade or the subclade containing most Haplosporidium species, but within a subclade of Haplosporidium sp. from Penaeus vannamei. Our results suggested that H. pinnae and the parasite of P. vannamei may represent a distinct new genus within the order Haplosporida., (Copyright © 2018 Elsevier Inc. All rights reserved.)

Understanding the respective roles of environment and interspecific interactions in shaping species' distributions is a critical aspect in determining the potential impacts of newcomer species on occupied habitats. The invasive caprellid amphipod Caprella scaura has successfully spread along southern Europe in a short time period, coinciding with a decline in the population of an ecologically similar congener, Caprella equilibra. To understand the mechanisms underlying the establishment success of this aggressive species and its potential role in shaping C. equilibra's distribution, we analyze the biotic and abiotic factors involved in the patterns of distribution and co-occurrence of both species along the Iberian Peninsula and northern Africa. Our analyses support that C. scaura is competitively displacing C. equilibra from the study area, but also point out the critical role of salinity and temperature in modulating this interaction and limiting the invasive success of C. scaura on the Iberian North-Atlantic coast., (Copyright © 2015 Elsevier Ltd. All rights reserved.)

Coastal degradation and habitat disruption are severely compromising sessile marine species. The fan shell Pinna nobilis is an endemic, vulnerable species and the largest bivalve in the Mediterranean basin. In spite of species legal protection, fan shell populations are declining. Models analyzed the contributions of environmental (mean depth, wave height, maximum wave height, period of waves with high energy and mean direction of wave source) versus human-derived stressors (anchoring, protection status, sewage effluents, fishing activity and diving) as explanatory variables depicting Pinna nobilis populations at a mesoscale level. Human stressors were explaining most of the variability in density spatial distribution of fan shell, significantly disturbing benthic communities. Habitat protection affected P. nobilis structure and physical aggression by anchoring reveals a high impact on densities. Environmental variables instead played a secondary role, indicating that global change processes are not so relevant in coastal benthic communities as human-derived impacts.

The pen shell Pinna nobilis (also known as the fan mussel) is an endemic bivalve of the Mediterranean Sea. Threatened by human activities, it has been listed as an endangered and protected species under the European Council Directive 92/43/EEC since 1992. The ecological role of this species is of importance because it filters and retains large amounts of organic matter from suspended detritus contributing to water clarity. In addition, as a hard substrate in the soft-bottom seafloor, it provides a surface that can be colonized by other (floral and faunal) benthic species. Here, we provide an overview of all available published studies on the pen shell, compiling available data and summarizing current knowledge on the conservation status and viability of populations over the full range of the Mediterranean Basin. Additionally, we discuss the different practices in applied methodology and identify gaps and new research areas in order to render conservation programmes of the species more effective., (© 2015 Elsevier Ltd. All rights reserved.)