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Patella ferruginea is the most threatened macroinvertebrate in the western Mediterranean, where it is at serious risk of extinction. There is little information on the status of the various populations and most data were published more than 25 years ago. This study provides updated information on the global status of this species, and implications for management and conservation, and tests the hypothesis that population structure can be influenced by collection by people and by the type of substrate. Fifty-five localities were surveyed in Corsica, Sardinia, Tuscany and Sicily, on the islands of Egadi and Pantelleria, and on the Zembra archipelago and Tunisian coasts. The species is extinct on mainland Italy and Sicily but isolated individuals can be found on Egadi and Pantelleria. Populations on Corsica and Sardinia have declined dramatically during the last 25 years. The population in the Zembra archipelago is well preserved, although more widely on Tunisian coasts the species is highly threatened. The information provided here, combined with information from the literature, indicates a strong decline and/or extinction of many populations throughout the western Mediterranean and the presence of healthy populations only in some locations along the north African coast. The species exhibits an increase in density and mean size in areas free of human pressure but the type of substrate (natural or artificial) has no strong influence.

Is the north side of the Strait of Gibraltar more diverse than the south side? A case study using the intertidal peracarids (Crustacea: Malacostraca) associated to the seaweed Corallina elongata jos e m. guerra-garci a, pilar cabezas, elena baeza-rojano, free espinosa and j. carlos garc ia-g omezThe objectives of this study were to describe the peracaridean fauna associated to the algae Corallina elongata from the Strait of Gibraltar, and explore possible biodiversity and biogeographical patterns of variation along the north-south and Atlantic-Mediterranean axes across the Strait of Gibraltar. Twenty-five stations were selected along the north and south coasts of the Strait to cover the broadest possible range of human pressure and environmental conditions, including both natural rocky shores and artificial breakwaters. The alga Corallina elongata was selected as substrate, and the peracaridean crustaceans were identified to species level and classified in geographical distribution groups. Univariate and multivariate analyses were conducted to explore and confirm patterns of variation. Forty peracarid species were collected, most of them with an Atlantic-Mediterranean distribution (67%) with only the gammarid Parhyale eburnea, being an endemic Mediterranean species. The most common species collected during the present study were the gammarids Hyale stebbingi, Jassa marmorata, Stenothoe monoculoides and Ampithoe spp., the caprellids Caprella grandimana and C. penantis, the isopod Ischyromene lacazei and the tanaid Tanais dulongi. The number of species per station and the diversity index were significantly higher in the stations located along the north side of the Strait of Gibraltar. However, the two-way ANOVA discarded differences between north and south due to the type of substrate (natural versus artificial) and degree of human pressure. Based on peracaridean assemblages, the Strait of Gibraltar behaves as a whole and homogeneous region, with a very similar faunal composition in all stations and there is not a clear gradient of species substitution from the Mediterranean to the Atlantic stations. Provided that we selected the same substrate in all stations, and that statistical analyses revealed that differences between north and south stations were not due to environmental factors such as anthropogenic stress or type of substrate, we should look to historical biogeographical reasons to explain the higher diversity in the north side of the Strait of Gibraltar.

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