Usefulness of marine protected areas as tools for preserving the highly endangered limpet, Patella ferruginea, in the Mediterranean Sea

ABSTRACT

Patella ferruginea is the most endangered endemic marine invertebrate of western Mediterranean rocky shores. From 2012 to 2015, we performed a census and an ecological study for this gastropod mollusc in the Zembra Archipelago National Park in Tunisia, where a large population still remains. In 1986, a total of 20,000 individuals were estimated, with 0.7 ind/m², 4.4 cm adult mean size and low recruitment rate. In 2009, the estimated population reached 38,559 individuals with 2.65 ind/m², 5.42 cm adult mean size and high recruitment rate. During the present work, 43,790 individuals were estimated in 2012, 27,359 in 2013, 33,170 in 2014 and 40,404 in 2015, with an average density ranging from 0.1 to 8.5 individuals per square metre, but reaching as many as 25 ind/m² on some shores. This makes the archipelago one of the most important Mediterranean ‘hot spots’ for P. ferruginea, as it has a large and well-conserved population of this species. Variability of the population size is influenced by various biotic and abiotic factors, but is principally impacted by poaching of the species. The poachers target individuals larger than 6 cm in length, and the sex ratio study has shown that over 70% of individuals become females at that size. In addition, high recruitment rates were recorded in 2012 and 2013, but these decreased in 2014 and 2015, although population numbers show the opposite pattern. Moreover, growth rate is low and P. ferruginea may need many years to reach a large adult size. The loss of reproductive potential due to poaching inevitably causes a significant imbalance in the limpet population. Our results indicate the importance of the National Park for P. ferruginea and underline the need for this species to be protected and monitored over a long period to provide the most appropriate management measures.

RESPONSIBLE EDITOR:

• Dan Smale

KEYWORDS:

• Census
• growth
• Patella ferruginea
• sex ratio
• Zembra
• poaching

Acknowledgements

The authors acknowledge their colleagues in the Coastline Protection and Management Agency (manager of Zembra National Park), National Institute of Agronomy of Tunisia, and Dr Carlos Navarro-Barranco from Marine Biology Laboratory of Seville University for their kind help with the fieldwork. We express our gratitude to the Tunisian General Directory of Forestry, Defense Ministry and National Guard for their help and support with this work.

Disclosure statement

No potential conflict of interest was reported by the authors.

ORCiD

Anis Zarrouk http://orcid.org/0000-0001-7753-5749

Free Espinosa http://orcid.org/0000-0002-1409-5106

Additional information

Funding

Special thanks go to the Coastline Protection and Management Agency, the MEDPAN association, and the Conservatoire du Littoral Français for their logistical and financial support.