The fan mussel (or noble pen shell), Pinna nobilis (‘nakkra’ in Maltese) is one of the best‐known marine invertebrates, representing an endemic flagship species for the Mediterranean Sea. The fan mussel is one of the largest bivalves in the world and the largest in the Mediterranean, reaching up to 120 cm in height and it is one of the most long‐lived, living up to 50 years in favourable conditions and recorded at depths between 0.5 and 60 m on soft bottoms. The species is strictly protected both at European, regional and national level.
Since 2016, starting from the Spanish coasts in the Alboran Sea in the western Mediterranean Sea, a still ongoing mass mortality event (MME), caused by a number of microbial species, has been decimating different Mediterranean populations of Pinna nobilis. In the western Mediterranean, for instance, as well as in the Adriatic and Aegean Sea, 100% mortality rates were recorded for surveyed noble pen shell populations. This disease outbreak compounds an already challenging conservation scenario for the species, which is subject to a number of human impacts, most notably anchoring and poaching by collectors.
A recently-completed study which made use of population data collected through SCUBA diving since 2006 as well as of data acquired through a citizen science campaign, has documented a relentless decline in the abundance of in-Nakkra within Maltese waters since 2006. Most of the marine sites surveyed in 2006 and in 2012 in fact did not record any live P. nobilis individuals in subsequent surveys.
The study also identified possible refuge areas for the handful of live P. nobilis individuals recorded during the MSFD surveys and citizen science campaigns and the study makes an impassionate appeal to conserve these sites and to monitor regularly individuals for both bivalve species and to introduce further conservation measures to protect the species. Interestingly enough, numbers for its sister species – the spiny fan mussel, ‘nakkra tax-xewk’ (Pinna rudis) were only found to marginally decline as a result of the disease in question.
The study is co-authored by Prof. Alan Deidun, Prof. Aldo Drago, Dr Adam Gauci, Dr Anthony Galea, Ms Raisa Tarasova, Mr Johann Galdies and Mr Alessio Marrone from the Oceanography Malta Group within the Department of Geosciences of the Faculty of Science, along with Prof. Simonetta Fraschetti from the University of Naples and coordinator of the AMARE project. The AMARE project, funded within the ambit of the Interreg MED 2014-2020 funding programme, came to a close in 2020 and funded the citizen science component of this study, which has been accepted for publication within a special edition of the Mediterranean Marine Science peer-reviewed journal, which will be released in June 2022.
