Patella Ferruginea Gmelin, 1791 (Gastropoda, Patellidae) on Algerian Islands (SW Mediterranean)

Animal Biodiversity and Conservation 32.1 (2009) 19 Populational status of the endangered mollusc Patella ferruginea Gmelin, 1791 (Gastropoda, Patellidae) on Algerian islands (SW Mediterranean) F. Espinosa Espinosa, F., 2009. Populational status of the endangered mollusc Patella ferruginea Gmelin, 1791 (Gastropoda, Patellidae) on Algerian islands (SW Mediterranean). Animal Biodiversity and Conservation, 32.1: 19–28. Abstract Populational status of the endangered mollusc Patella ferruginea Gmelin, 1791 (Gastropoda, Patellidae) on Algerian islands (SW Mediterranean).— Patella ferruginea is the most endangered endemic marine invertebrate on the Western Mediterranean coasts according to the European Council Directive 92/43/EEC. A total of 1,017 individuals were recorded in the present study along western Algerian islands, with mean densities ranging from 0.8 to 35.3 ind/m per linear transect and averages of 4.8 ind/m per linear transect for Western Habibas Island and 22 ind/m for Plane Island, making these islands a hot spot for the species in the Medi- terranean. The expected total number of specimens in Habibas would therefore be 50,400. The mean size of P. ferruginea on the Habibas Islands (4.45 cm) was significantly p( < 0.001) greater than on Plane Island (2.78 cm). Recruitment was high in Plane Island and the northern sector of the western Habibas Islands. Lar- ge adults had very conical shells. The fact that Habibas Islands is now a marine reserve could explain these differences in populations. Conservation of these populations should be a priority in order to avoid extinction of the species. Key words: Patella ferruginea, Algeria, Conservation, Limpet. Resumen Estado de las poblaciones del molusco protegido Patella ferruginea Gmelin, 1791 (Gastropoda, Patellidae) en las islas argelinas (SO Mediterráneo).— Patella ferruginea es el invertebrado marino endémico más amenazado de las costas del Mediterráneo occidental según la Directiva 92/43 de la Unión Europea. En este estudio se registraron un total de 1.017 ejemplares en las islas occidentales argelinas, con densidades medias de 0,8 a 35,3 ind/m de transecto linear y valores medios de 4,8 ind/m en la isla Habibas occidental y de 22 ind/m en la isla Plana. Estas poblaciones representan un "punto caliente" de la especie a nivel de todo el Mediterráneo. La estima de población para las islas Habibas es de 50.400 individuos, uno de los más elevados para la especie. La talla media de P. ferruginea fue significativamente (p < 0,001) mayor en la isla Habibas occidental (4,45 cm) que en la isla Plana (2,78 cm). El reclutamiento fue muy elevado en la isla Plana y en el sector norte de la isla Habibas occidental. Los ejemplares de mayor talla muestran conchas muy cónicas. El establecimiento de una reserva marina en las islas Habibas podría explicar las diferencias halladas entre las poblaciones. La conservación de estas poblaciones debe ser una prioridad para evitar la definitiva extinción de la especie. Palabras clave: Patella ferruginea, Argelia, Conservación, Lapa. (Received: 4 VII 08; Conditional acceptance: 17 X 08; Final acceptance: 20 I 09) Free Espinosa, Lab. de Biología Marina, Depto. de Fisiología y Zoología, Fac. de Biología, Avda. Reina Mercedes 6, C. P. 41012, Sevilla, España (Spain). ISSN: 1578–665X © 2009 Museu de Ciències Naturals 20 Espinosa Introduction Material and methods Patella ferruginea Gmelin, 1791, endemic to the Study area Mediterranean, is the most endangered marine invertebrate on Western Mediterranean rocky shores The study was conducted during April 2008 on the according to European Council Directive 92/43/EEC Western Habibas and Plane Islands. Located off the on the Conservation of Natural Habitats and of Wild West coast of Algeria (fig. 1), these islands are under Fauna and Flora, 1992 (Ramos, 1998), and it is the influence of the Atlantic waters from the Alborán presently under serious threat of extinction (Laborel– Sea (Robinson et al., 2001) and they are located at Deguen & Laborel, 1991; Templado & Moreno, 1997). the southern end of the Almería–Orán oceanographic This is a long–lived protandrous hermaphrodite front (see Templado et al., 2006). The approximate (Espinosa et al., 2008) that achieves sexual matu- perimeter of the Habibas Islands is 10,500 m and the ration as a male from 20–30 mm and then changes substrate is composed of rocky shores of volcanic to female around 42–60 mm, although males can origin (Ben Haj & Bernard, 2005), without presence of be observed up to 80 mm (Espinosa et al., 2006; sandy or boulder beaches. The shoreline is twisting Guallart et al., 2006a). It requires clean waters and with several separate small islets. The distance from medium–strong wave action (Espinosa, 2006). Study Habibas Islands to the nearest mainland is 9.5 km, of the population status of the species and relevant whereas for Plane Island the distance to the nearest pressure factors indicate better management and mainland is about 5 km. The distance between the conservation measures are essential. two islands is 20 km. Population size structures, in the sense of dis- tribution of body size within particular populations, Sampling methods are affected by environmental changes, ecological interactions and, in many cases, human exploitation. Four sectors were considered in Western Habibas These structures are an important indicator of the Island (East, South, West and North) and three population status and can be used comparatively delimited transects were established inside each across sites and through time to identify the forces sector (fig. 1, table 1). In Plane Island two transects controlling population dynamics. Size structures also were located, approximately in the West and North have been used to track losses of large individuals areas, because the reduced size and regular shape from populations which are often the target of ex- of the island made it difficult to establish different ploitation by humans (Rochet & Trenkel, 2003), as sectors. The transects were 10 metres in length occurs with limpets, which are collected as food or (Laborel–Deguen & Laborel, 1991; Guerra–García as fishing bait because of their large muscular foot et al., 2004), of similar slope (30º–60º) and were (Pombo & Escofet, 1996). Human exploitation can measured with a tape measure to follow the coast also decrease the reproductive output of intertidal profile. Collected P. ferruginea specimens were invertebrate populations in which there is an increase measured with a calliper to the nearest mm on their in individual fecundity with body size (Levitan, 1991; longitudinal axis (Guerra–García et al., 2004). All Tegner et al., 1996), and such is the case with P. individuals found above or under the transect tape ferruginea Gmelin, 1791 (see Espinosa et al., 2006). were recorded and measured. As small individuals All of these considerations are especially true for are difficult to detect (Guallart et al., 2006b), care broadcast spawners such as limpets that depend was taken to observe this fragment of population. on high gamete concentrations to increase the pro- bability of successful fertilisation (Hockey & Branch, Data analysis 1994) and avoid the ‘Allee’ effect (Courchamp et al., 2008). As with many ecological impact data (Clarke & The Western Algerian Islands (Rachgoun, Habi- Warwick, 2001), the assumptions for parametric sta- bas and Plane) are sites of high ecological value tistics are not met by some of our data, which have given the number of endemic and endangered severe departures from normality and equal variances. Mediterranean marine species living there (Bachet The ANOVA test is, however, robust for deviation et al., 2007). Important populations of the endan- from normality and if the number of cases is high and gered mollusc P. ferruginea Gmelin, 1791 have balanced between groups it is possible to undertake been recorded on Rachgoun (Frenkiel, 1975) and the analysis even if the condition of equal variances Habibas Islands (Boumaza & Semroud, 2001). The is not met (Underwood, 1997). Only one ANOVA test latter islands were declared a Marine Natural Re- without equal variances was performed with the large serve in 2003 by the Algerian Government (decree dataset pooled in the Habibas and Plane sites for nº 03.147, 29 March) (Ben Haj & Bernard, 2005). mean sizes. The rest of the analyses performed were The aim of this study was to determine the po- checked for homogeneity of variances by means of the pulation parameters (size frequencies and density) Levene test and the use of logarithmic transformation of the P. ferruginea population at the Western Habi- when required to satisfy homocedasticity. Differences bas and Plane Islands. Such information would be between means were examined a posteriori with the useful in order to detect future changes produced Student–Newman–Keuls test. Reduction of data only by pressure factors such as human collecting or to summary statistics such as mean sizes greatly predation. reduces the information available for comparisons Animal Biodiversity and Conservation 32.1 (2009) 21 Cape Falcon Habibas Island Plane Island Orán 35º 44' Eastern Island N 50 m North Western Island West East South 35º 43' 500 m 8º 7º Fig. 1. Map of the study site showing the location of Habibas and Plane Islands. In Western Habibas Island the perimeter was divided into four sectors: East, South, West and North (spots indicate the sampling sites for Patella ferruginea). Fig. 1. Mapa del área de estudio, mostrando la situación de las islas Habibas y de la isla Plana. El pe- rímetro de la isla Habibas occidental se dividió en cuatro sectores: este, sur, oeste y norte (los círculos negros indican los lugares de muestreo para Patella ferruginea). (Sagarin et al., 2007). Therefore, multivariate MDS to the extreme variability within sectors, although (non–metric multidimensional scaling) statistics were the North sector showed the greatest densities of P. additionally used, based on the UPGMA method ferruginea.

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