‘Impossible’ re-introduction of the endangered limpet Patella ferruginea Gmelin, 1791? Progress in resolving translocation mortality

The Mediterranean ribbed limpet Patella ferruginea Gmelin, 1791 is the most endangered marine invertebrate listed in the EU Habitats Directive. A diversity of anthropic pressures have reduced its present-day distribution to a fraction of its former size. Perhaps surprisingly, this highly protected species has successfully established along man-made harbour breakwaters, resulting in serious complications when these structures have required modification or repair, often leading to costly impasses due to the legal status of the species. Attempts to move the limpets to other locations have resulted in unacceptably high mortality rates. This article describes the result of a field experiment where 97 P. ferruginea individuals were transported to a new site, using a technique which involved carefully moving the limpets whilst inactive (during low tide), still attached to their home scars on breakwater boulders. The results of this experiment were significantly positive, with 87 % of all translocated limpets still alive 10 mo after the move, a mortality rate which compared favourably with that obtained for the existing control population at the receptor site. We propose that this method could be a practical solution to address the conflicts generated by this endangered species' preference for harbour constructs. We further propose that this method can be used as a management tool to enhance the species' survival prospects, by creating 'stepping stones' of pockets of reproducing individuals that can connect currently fragmented populations to effect a population recovery of this threatened organism.