Disease is an increasing threat for marine bivalves worldwide. Recently, a mass mortality event (MME) impacting the bivalve Pinna nobilis was detected across a wide geographical area of the Spanish Mediterranean Sea and linked to a haplosporidian parasite. In 2017–2018, mass mortality events affecting the pen shell Pinna nobilis were recorded in two different regions of Italy, Campania and Sicily, in the Tyrrhenian Sea (Mediterranean Sea). Histopathological and molecular examinations of specimens showed the presence of Haplosporidium sp. in only one specimen in one area. Conversely, in all of the surveyed moribund animals, strong inflammatory lesions at the level of connective tissue surrounding the digestive system and gonads and linked to the presence of intracellular Zhiel-Neelsen-positive bacteria were observed. Molecular analysis of all of the diseased specimens (13) confirmed the presence of a Mycobacterium. Blast analysis of the sequences from all of the areas revealed that they were grouped together with the human mycobacterium M. sherrisii close to the group including M. shigaense, M. lentiflavum and M. simiae. Based on pathological and molecular findings, it is proposed that a mycobacterial disease is associated with the mortality episodes of Pinna nobilis, indicating that, at this time, Haplosporidium sp. is not responsible for these events in Campanian and Sicilian waters.

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.

11 páginas, 4 tablas, 6 figuras.In this study, we examine the hypotheses that the size of the seagrass meadow and\ud marine protection influence the abundance of seagrass herbivores and their associated grazing pressure. The effect of meadow size was tested in 9 shallow unprotected meadows of Posidonia oceanica\ud encompassing a wide range of areas. The effect of fishing protection was examined by comparing\ud 9 unprotected meadows (controls) with 3 marine protected areas (MPAs) with at least 20 yr of protection that also varied in meadow size (large >3 ha, medium 1 ha < x < 2 ha and small <1 ha). At each\ud site, we quantified the abundance, size distribution and grazing pressure of the 2 most important herbivores, the fish Sarpa salpa and the sea urchin Paracentrotus lividus. A strong negative relationship\ud between meadow size and both the abundance and grazing rates of S. salpa was evident in the\ud unprotected meadows, but no effects were detected on either the abundance or grazing rates of\ud P. lividus. Results also showed that populations of S. salpa (mainly large individuals) benefit from\ud fishing protection and tended to concentrate in MPAs (with the exception of Port-Cros), resulting in\ud enhanced grazing pressure. In P. lividus abundances or size distributions did not present any significant difference between protected and unprotected areas, although most MPAs presented low sea\ud urchin densities. While MPAs are important to preserve seagrass ecosystems, results from this study\ud indicate that it is crucial to account for the size of these habitats, particularly when functional aspects\ud of seagrass habitats are so strongly altered by size.This work was supported by a FI scholarship from the Departament d’Universitats, Recerca I Societat de la Informació (DURSI, Generalitat de Catalunya) to\ud P. P., and the CGL2007-66771-C02/BOS project funded by the\ud Spanish Ministry of Science and Technology.Peer reviewe

7 páginas, 4 figuras.Predation on sea urchins, which are important structuring agents in seagrass communities, can be modulated by habitat structural complexity. Here we examine the importance of meadow\ud structure (leaf length and presence of unburied root-rhizome layer) in determining predation pressure on the main invertebrate herbivore of the temperate seagrass Posidonia oceanica (L.) Delile, the\ud sea urchin Paracentrotus lividus (Lamarck). The attributes of seagrass habitat complexity are subject\ud to considerable spatial and temporal variability, thus affecting refuge availability. In the field, exposure of the root-rhizome layer depends on local sedimentary conditions, while changes in the leaf\ud canopy are generally dictated by hydrodynamic regimes, light, nutrient availability as well as grazing activity. We reproduced 5 habitat conditions in the laboratory and 2 in the field by modifying leaf\ud length and burial level of the root-rhizome layer, and we measured fish predatory efficiency under\ud controlled conditions. In the laboratory we focused on juvenile sea urchins (0.2 to 1.2 cm test diameter, TD) while in the field we studied young adults (3 to 5 cm TD). Mortality of juveniles and young\ud adults was significantly lower under long leaves, while the presence of an unburied root-rhizome\ud layer appeared to provide a key refuge for juveniles, independent of leaf length. The presence of\ud refuges thus appears to be a key factor in the interaction between sea urchins and predatory fish in\ud seagrass meadows, and highlights the importance of local structural complexity (e.g. sedimentary\ud regimes, fish herbivory pressure) on the regulation of predator–prey interactionsThis work was\ud supported by plan CGL2007-66771-C02-01 from the Spanish\ud Ministry of Science and Education.Peer reviewe