Pinna nobilis Linnaeus, 1758

Noble pen shell (Pinna nobilis) is an endemic species with rich history and of special significance for the marine ecosystem. We are not familiar with bigger bivalves in the Mediterranean than the noble pen shell, and we cannot find this species anywhere else than this unique, enclosed sea. Noble pen shell individuals can grow more than a meter in length, weigh more than three kilograms and can live as long as 50 years. It is distributed in shallow areas, where tides are present, leaving a pen shell partly outside of the water. It is present even at depths of 60 meters, but it is most numerous on seagrass meadows, where it uses its byssus threads to attach itself into the substrate and become a part of one of the most productive marine habitats.

The Noble pen shell offers a hiding place, feeding ground and nursery for a great number of organisms that we know by a single name; epibionts. The colonization of this bivalve as a hard substrate was shown as a great strategy for survival of immobile, but also mobile organisms. Sometimes, one individual can harbor more than 35 species of animals and algae.


Autumn 2016 was marked by the beginning of one of the hardest and most disastrous periods in the history of noble pen shell existence. A newly discovered parasite, Haplosporidium pinnae, in synergy with the bacterium, Mycobaterium sherrisii, killed noble pen shell populations on Spanish Balearic, and by 2020, these pathogens uncontrollably dispersed throughout the Mediterranean and infected almost all individuals in the wild. Today we count only a few dozen live pen shells in salty lagoons in France, Spain and Turkey.

Learn more about mass mortality   Effect on Noble Pen Shell

Parasite affects noble pen shell in a way that it inhabits the digestive gland and causes an infection of epithelial cells, decreasing filtration activity of the bivalve. The mantle of the hungry individuals reduces, and the pen shell loses its ability to close properly. Death is a final result of the infection. Parasite reproduction is induced at temperatures above 13.5°C and salinity in the range between 36.5 and 39.7 ppm. Under these conditions, it can spread up to 300 kilometers in only one season. In synergy with the bacteria Mycobaterium sherrisii, Haplosporidium pinnae is considered as a main cause of the noble pen shell mass mortality event.

In the beginning, it was considered that the Balearic Islands are the primary and only infected zone, but in less than a year, this parasite killed natural noble pen shell populations in Spain, France, Italy and Tunisia, and during 2018, it killed pen shells in Libya, Egypt, Israel, Cyprus, Turkey and Greece. The year after that, the parasite continued its dispersal to the north destroying populations in Albania and Montenegro, and by the middle of the year, parasite presence was detected in the southern Adriatic. The parasite continued to spread from Elaphiti Islands all the way to the mid-Adriatic. In April 2019, the first positive results of the H. pinnae presence in the tissue of noble pen shell from NP Mljet were obtained.


During the field evaluation of NP Mljet in 2019, together with associates from the University of Dubrovnik, the Aquarium Pula team witnessed a noble pen shell mass mortality event. That disastrous sight was an incentive to implement conservation actions regarding preservation of any last viable individuals in the northern Adriatic, which were approved by the Ministry.

Due to the alarming situation for noble pen shells in the Mediterranean, Aquarium Pula, with the financial help from the European Union of Aquarium Curators (EUAC), took adequate preventive actions and became a first reception center known by the name “Noble Sanctuary“.


The Ministry of Nature Conservation and Energy gave us a permission to gather and keep 33 healthy individuals from coastal areas in Pula in June 2019. Except for everyday monitoring of parameters, construction of live food culturing establishment for large filtrates was needed. Seeing as the end of 2019 was marked by the mass mortality event of pen shells in the Bay of Trieste, and not long after that in Piran's aquatorium, persuaded us to ask for the Ministry's permission to isolate individuals from other locations.
Pathogen analysis for Haplosporidium pinnae and Mycobacterium spp. was conducted in the Croatian veterinary institute (HVI) for every individual on three tissue samples (mantle, adductor muscle and digestive gland). Analysis was conducted exclusively on dead or sacrificed individuals. To check the condition of noble pen shells in the northern Adriatic, we tested three individuals from three locations (Pula-Stoja, Ližnjan and Peroj). After receiving negative results on H. pinnae and M. sherrisii., we isolated 34 individuals from the location “Valovine“ in Pula on October 4, 2019, and placed them in separated tanks. Unfortunately, after some time, we detected changes in the speed of shell opening and closing, and also the look of the mantle. That was the time when first individuals in the Sanctuary started to die off. Analysis conducted on dead individuals showed that those individuals were infected with M. Sherrisii (19th February 2020 and 27th May 2020). From 34 viable pen shells until today (25th January 2021), there is only one individual left alive.
Other three groups came from three different locations: Vinkuran, Štinjan and Rovinj, in February 2020. From each group, at their arrival, one sacrificed individual was tested. Results of the analysis of H. pinnae and of M. sherrisii were negative. Unfortunately, with the increase of sea temperature (in May 2020), a significant mortality occurred. We tested three dead individuals. Results showed that all three were already infected with H. Pinnae, and two of them also had M. sherrisii present in their tissues. Our’s and the opinion of the Veterinary Institute, was that all of these individuals that arrived at the Sanctuary in February 2020 were already infected, but because of lower temperatures, we weren't able to detect the presence of the parasite.
First online IUCN (International Union for Nature Conservation) congress, at which we presented our results, showed us new knowledge gathered about the situation with wild pen shells across the Mediterranean; a small number of individuals are alive in France, Spain and Turkey, while a few scientific institutions and aquariums are keeping around a hundred live pen shells, of which the most is kept in Spain.

NEW HOPE – Young noble pen shells

dr. sc. Tatjana Bakran-Petricioli and dr. sc. Silvija Kipson successfully implemented transplantation of noble pen shells from the harbor of Pula into the NP Brijuni in 2017 through the project MERCES (Marine Ecosystem Restoration in Changing European Seas). They realized that it is possible to gather noble pen shell larvae from locations affected by mass mortality event and bring them to safety. They launched the initiative of placing larvae collectors through a new project called “PinnAdriaNet“, where many partners from academic, research and public institutions, and NGO's throughout Croatia. This project resulted by signing the agreement with the Ministry of Economy and Sustainable development in 2020, when Aquarium Pula became a leading institution in Croatia responsible for keeping young and adult individuals in controlled (ex-situ) conditions. Funding also co-finances individual activities that are carried out by our partners: monitoring of locations with surviving individuals, placing larvae collectors, keeping adult and young individuals in controlled conditions (ex-situ) and raising public awareness through different education activities.
Within the project, collectors for young individuals were placed on 15 different locations across the Adriatic. Placing was conducted in June 2020, and they were extracted by the end of the year. Fifteen larvae were found on three locations, and those individuals are kept in quarantine at Aquarium Pula. Specially treated, purified, UV sterilized and filtered seawater is used for keeping young individuals. Young pen shells are held in tanks with an enclosed system and separated in groups by a location on which they were found. All parameters of the system; temperature, salinity, pH, oxygen concentration and metabolic excretions (ammonia, nitrites, nitrates) are controlled daily. It is crucial to feed them multiple times every day. Food is composed out of unicellular algae – phytoplantkon (Tysochrisis sp., Tetraselmis sp., Nanocloropsis sp. and diatoms) with a little bit of zooplankton

U sklopu projekta postavljeni su kolektori za prihvat mlađi periske na 15 lokacija diljem Jadrana. Postavljanje je provedeno u lipnju 2020. godine, a kolektori su izvađeni i pregledani krajem godine. Na tri lokacije pronađeno je sveukupno 15 mladih jedinki koje se danas nalaze u karantenskom odjelu Aquariuma Pula. Za njih se koristi posebno pripremljena morska voda, pročišćena i kontinuirano tretirana UV svjetlom te filtrirana na 1 mikrometar. Mlade periske nalaze se u bazenima zatvorenog sustava, a s obzirom na lokaciju pronalaska podjeljene su na tri skupine; Omišanka, Brionke i Rovinjke. Svi se parametri sustava; temperatura, salinitet, pH, i količina kisika, nusproizvodi metabolizma (amonijak, nitriti, nitrati) svakodnevno kontroliraju te se strogo održava čistoća. Budući da se radi o juvenilnim jedinkama, potrebno ih je svakodnevno hraniti više puta. Hrana se sastoji od različitih vrsta jednostaničnih algi, odnosno fitoplanktona (Tysochrisis sp., Tetraselmis sp., Nanocloropsis sp. i alge kremenjašice) uz mali dodatak zooplanktona.


The first young pen shell arrived at the aquarium on November 19th, named “Omišanka”, Jelena Kurtović Mrčetić, a biologist from the Public Institution “More i Krš“, found a young pen shell, 1.5 cm in length, in the harbor of Omiš at the depth of 6 meters, after thorough collector inspection. A few days later, “Rovinjke“ arrived, an individual found after collector inspection in the bay of Leso, headed by dr. sc. Andrej Jaklin. At the end of the December, “Brionke“ also arrived at Aquarium Pula. They were found during a careful inspection of larvae collectors located in NP Brijuni, and the team headed by dr. sc. Tatjana Bakran-Petricioli delivered them to the aquarium. Young individuals are fed multiple times during the day: by hand (at least four times) and with the help of an automatic feeder (every hour).
Prva jedinka periske pristigla je u pulski akvarij 19. studenog, nazvana „Omišanka“. Jelena Kurtović Mrčetić, biolog iz Javne Ustanove More i Krš, nakon pomnog pregleda kolektora na 6 metara dubine u Maloj Luci u Omišu, pronašla je mlađ periske, veličine 1,5 cm. Nekoliko dana kasnije pristigle su „Rovinjke“, jedinke pronađene tijekom pregleda kolektora u uvali Leso pod vodstvom Andreja Jaklina. Krajem prosinca, pristigle su i „Brionke“. Pronađene su tijekom pažljivog pregleda kolektora postavljenih u Nacionalnom Parku Brijuni, a tim pod vodstvom Bakran-Petricioli ih je predao Aquariumu Pula. Hrane se više puta dnevno: ručno (najmanje 4 puta) te uz pomoć automatske hranilice (svakih sat vremena).


Public education about problems that marine ecosystems encounter was always a key part of conservation of nature and its resources. Knowing that, Aquarium Pula accomplished a series of achievements regarding raising public awareness about possible noble pen shell extinction. The main goal was to introduce the public with our activities, to sensitize people and give them an incentive to become involved in the conservation of this noble species. Numerous reports from the field are given by citizens, and are mostly essential and needed to get the bigger picture about the status of the population in need of our protection.

NOBLE SANCTUARY – a documentary

A short documentary “Noble Sanctuary“, shows the noble pen shell as the biggest Mediterranean bivalve whose absence would negatively affect the balance of the marine ecosystem that we know today. It introduces the audience to the mass mortality event, the unexpected pathogen spread that brought the noble pen shell at the brink of extinction. Watch “Noble Sanctuary“ and follow the activities of the scientific community and Aquarium Pula staff that dedicate their time and resources to noble pen shell conservation.
The documentary was premiered at the 67th Pula Film Festival within a non-competitive program, and was shown multiple times in the exhibition “The Treasure of the Adriatic Seabed“ within the series “Save noble pen shell from extinction“ sponsored by the City of Crikvenica.