Tracking a mass mortality outbreak of pen shell Pinna nobilis populations: A collaborative effort of scientists and citizens.

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.

Changes in body condition and fatty acid composition of wild Mediterranean horse mackerel (Trachurus mediterraneus, Steindachner, 1868) associated to sea cage fish farms.

Net-cage fish farms attract a great number of wild fishes, altering their behaviour and possibly their physiology. Wild Mediterranean horse mackerel (Trachurus mediterraneus), sampled from populations aggregated around two Mediterranean fish farms and from two natural control populations, were analyzed for differences in body condition, stomach content and fatty acid composition. Pellets used to feed caged fish in both farms were also analyzed to identify their relationship with the fatty acid composition of tissue of wild fish. T. mediterraneus aggregated around the farms throughout the year although large seasonal changes in abundance and biomass occurred. Wild fish aggregated at farms mainly ate food pellets while control fish fed principally on juvenile fish and cephalopods. Wild fish that fed around the cages had a significantly higher body fat content than the control fish (7.30+/-1.8% and 2.36+/-0.7%, respectively). The fatty acid composition also differed between farm-associated and control fish, principally because of the significantly increased levels of linoleic (C18:2omega6) and oleic (C18:1omega9) acids and decreased docosahexaenoic acid (C22:6omega3) in farm-associated fish. The increased condition of wild fish associated with farms could increase the spawning ability of coastal fish populations, if wild fish are protected from fishing while they are present at farms. The fatty acids compositions could also serve as biomarkers to infer the influence of a fish farm on the local fish community, helping to better describe the environmental impact of fish farming.