The endangered status of Patella ferruginea in a limpet assemblage hotspot (Plane Island: South West Alboran, Mediterranean Sea): Local distribution factors and species abundance

Limpets constitute an important key species in the intertidal zone. The limpets’ assemblage is evaluated in Plane Island (Paloma Island, Algerian West coast) by detailed censuses which were performed in 8 zones in the main island and 9 islets. Results allowed the estimation of a total population of 3993 of the endangered Patella ferruginea (1.78ind/m), 1861 P. rustica (0.82ind/m), and 383 of the blue Mediterranean limpet P. caerulea (0.17 ind/m). The ferruginous limpet distribution around Plane Island was influenced by abiotic factors as hydrodynamics and the sea current direction. Conversely, anthropogenic factors had an important impact despite the island's distance from the mainland. This study finds that in the face of global warming, the island surface will be reduced, however limpets will have an important contribution to the island's areas and its conservation of biodiversity.

Filling gaps: closing the life cycle of the endangered Mediterranean limpet Patella ferruginea Gmelin, 1791 (Gastropoda, Patellidae)

Several reproductive issues and the larval development of the ferruginous limpet, Patella ferruginea Gmelin, 1791, an endangered species endemic from the western Mediterranean Sea, were studied to fill gaps in the knowledge of its life cycle.Average diameter of mature oocytes was 141.83 μm and mean oocyte density in the ovary was 283,800 oocytes/gram. No significant correlations were found between both oocyte diameter or density and female shell length. Female fecundity (number of oocytes per gonad) was significantly correlated with shell length and varied between 189,200 oocytes in a 40.0 mm female and 5,019,200 oocytes in an 86.4 mm female. However, there was considerable variability, in particular for largest females.Spawning induction was not achieved using usual molluscan aquaculture methods. Thus, oocytes obtained after dissection of females were used for fertilizations trials. Alkalinization treatments of seawater were used to test improvement in oocyte maturation and later fertilization rates. Treatment at pH 9 during 2 h produced the highest increase in the percentage of mature oocytes and in the fertilization rate; but these results showed high variability and were mainly significant when the initial degree of maturation was low. Sperm concentration experiments determined that best in vitro fertilization were performed at 105 and 5×105 spermatozoids/ml. The sequence and timing of the complete larval development of Patella ferruginea in laboratory conditions is described and illustrated here for the first time. At 20 °C, larvae became competent for metamorphosis 3 days after fertilization, but some crawling pediveliger larvae with a still well developed velum were found even 7 days after fertilization. Recruits 1-2 mm in length were achieved in low numbers from two of the last assays and were first detected between 131-141 days after fertilization. The resulting juveniles were monitored during two years and sex determination of five survivors at the end of this period showed that two were mature males, two mature females and one indeterminate.Our results show that the main reproductive traits or larval development of P. ferruginea hardly differ from those of other non-endangered Mediterranean or NE Atlantic limpet species. Therefore, its decline cannot be mainly attributed to some constraints of these traits as was previously suggested, but to human impact.On the other hand, it is feasible to complete the life cycle of this species in laboratory conditions, from fertilized eggs to mature individuals. However, an important part of the process like spawning induction was not achieved as gonads needed to be dissected fatally from females, although sperm could be obtained from males through non-lethal biopsies. At present, large-scale aquaculture production for reintroduction, restocking or stock enhancement purposes is neither possible nor an advisable conservation tool yet. Further study is required and meanwhile, an appropriate design of a network of effectively protected marine areas that ensures connectivity among extant populations is necessary.

Distribution of the Mediterranean ribbed limpet Patella ferruginea Gmelin, 1791 along the Ligurian coast and implications for conservation actions

Patella ferruginea is an endemic limpet of the Western Mediterranean Sea, presently considered the most threatened marine macroinvertebrate in the region and included in several international conservation directives. Its populations were widespread throughout the Western Mediterranean in the late Pleistocene (Tyrrhenian period), still largely distributed until the 19th century and presently confined into small populations in few restricted areas due to human harvesting for food and baits, construction of coastal infrastructures and the effects of seawater pollution. In particular, the species was reported as presently missing in the whole of the Italian continental coasts and measures are in progress to reintroduce the species through translocation and reproduction in controlled conditions along the Ligurian coasts (North-western Mediterranean).Recent surveys along the Ligurian coasts, performed to assess the most suitable sites for reintroduction, allowed the discovery of 32 specimens of this endemic limpet, considered disappeared in the area. These findings shed new light on the ability of natural dispersion of the species, the relevance of the measures set in place to restore the presently rarefied populations and provide hints for the selection and management of sites within the Natura 2000 Ecological network.