Distribución y censo actualizado de la lapa ferrugínea (Patella ferruginea Gmelin, 1791) en el litoral de Melilla (Mediterráneo suroccidental)

The population of the ferrugineous limpet (Patella ferruginea), a species in risk of extinction, is evaluated in the whole littoral of the Autonomous City of Melilla (Spain) by sampling done between March and June, 2010. Moreover, detailed censuses were performed in eight transects distributed along the coastline. Results allow to estimate a total population of 32,821 adult specimens (shell maximum diameter larger than 30 mm). The population shows a well structured size/age distribution, with a wide range of sizes from young to large individuals, but specimens larger than 90 mm are scarce. Patella ferruginea is distributed in Melilla both on the natural rocky shores and on the numerous artificial structures which constitute more than a half of the littoral. It should be pointed out its abundance on the external breakwater of the Melilla port, where is concentrated the 68.1% of the estimated population. The average density of adults for the whole littoral (excluding coastal zones with unsuitable habitats for the species) is 2.8 adults/m, with a maximum value of 66.5 adults/m in a transect. Excepting zones with unsuitable substrate (beaches), P. ferruginea is lacking in the 44.0% of the littoral of Melilla, which corresponds to the inner port areas and the littoral stretches where coastal works have been done recently. Comparison between data of 2010 and 2006 shows that coastal works done during those four years may have meant the disappearance of about 1,900 adult individuals of P. ferruginea, in zones where recolonization on the new installed substrates seems to have hardly begun nowadays. Despite of that mortality, the present global estimation of the population means an increase of 69.2% with regard to the 2006 estimation, mainly due to the more detailed study of some zones, specially the external breakwater of the port. The results pointed out that the littoral of Melilla is one of the few places in which there is still an important population of this endangered limpet, and therefore it should be considered a critical area whose right management is essential for the survival and recovery of the species.