The noble pen shell, known as Pinna nobilis, is an emblematic and endemic species of the Mediterranean Sea; meaning, it cannot be found anywhere else in the world. It is the largest bivalve mollusk in this sea and the second longest in the world, reaching up to 1.2 meters in length, surpassed only by the tropical species Tridacna gigas. Despite its rapid growth (able to exceed 20 centimeters in its first 2 years), it remains relatively unknown.
Specimen of noble pen shell (Pinna nobilis) among the leaves of the seagrass Posidonia (Posidonia oceanica) in Calpe. Photo: Sebastián Hernandis.
Emblem of the Mediterranean: Size and Significance
It’s true that bivalves are a less popular group compared to the charm of turtles or dolphins. Moreover, being second in something can often mean being forgotten—think of the second man to walk on the moon. Being an endemic species highlights its value, but it logically makes it less known in places where it is not present.
Natural History and Ecological Role of the Largest Bivalve Mollusk in the Mediterranean
Due to its large size, the noble pen shell has few natural predators, with adult specimens only threatened by strong storms or octopuses. The former can be lethal due to strong hydrodynamics, while the latter are among the few animals capable of prying open their shells through sheer force, though this isn’t an easy battle for them. The noble pen shell is a filter feeder, relying on passing water through its gills to capture food. In English, it’s known as the “fan mussel,” due to its triangular fan-shaped shell. In its natural habitat, we typically see only about two-thirds of its total size, as the last third is buried in the substrate, anchored to the seabed by fibers known as byssus.
Octopus (Octopus vulgaris) with a noble pen shell (Pinna nobilis) shell. Octopuses are among the few predators of noble pen shells. In this case, it is using a shell of a deceased noble pen shell to cover itself in its hole. Photo: Sebastián Hernandis.
There’s limited research, but it’s known these animals are hermaphrodites, able to mature both reproductive organs asynchronously during breeding season. To reproduce, they release gametes into the water, relying on chance and natural selection for fertilization and larval survival. There’s suspicion that there may be some synchronization mechanism among individuals for group gamete emission.
Their habitat ranges from shallow areas at 1-2 meters deep to 50 meters, usually within meadows of the seagrass Posidonia oceanica, another endemic and iconic species shaping one of the Mediterranean’s most distinctive ecosystems.
Specimen of noble pen shell (Pinna nobilis) among the leaves of the seagrass Posidonia (Posidonia oceanica) in Moraira. Photo: Sebastián Hernandis.
Threats to Survival: Disease and Environmental Degradation
Until a few years ago, noble pen shells were relatively easy to spot among Posidonia leaves due to their size. However, since late 2016, a disease caused by a previously unknown protozoan has decimated populations in the southern Spanish Mediterranean. This protozoan, Haplosporidium pinnae, quickly spread via currents throughout the Mediterranean, resulting in near 100% mortality in affected populations. The noble pen shell’s situation is critical, leading the International Union for Conservation of Nature (IUCN) to declare it critically endangered.
Few populations remain free from this parasite. In Spain, only two surviving populations are known, located in the Ebro Delta and the Mar Menor. Why these populations have remained healthy is unknown, though partial isolation from open seas and specific physicochemical conditions (like salinity) might prevent parasite entry. Despite their survival so far, the future looks bleak for the species in terms of recovery. No individuals resistant to the disease have been found, and the protozoan’s persistence could prevent Mediterranean populations from recovering.
Several specimens of noble pen shell (Pinna nobilis) in the Posidonia (Posidonia oceanica) meadow in Calpe. Photo: Sebastián Hernandis.
Conservation Efforts: A Call to Action
Adding to the challenge, the Mar Menor—a sanctuary for these giant mollusks—is facing an environmental crisis due to agricultural pollution and unchecked urban development, which could deliver a final blow to a species already on life support.
Each noble pen shell is crucial to the species’ recovery, especially those in open seas, as they might hold the key to disease resistance. Despite high mortality rates, hope remains that such individuals exist, yet the vastness of the sea versus the few survivors complicates finding them. Therefore, collaboration from divers, fishermen, and snorkelers is crucial. If you spot a noble pen shell during your underwater activities, taking photos, noting GPS coordinates, and contacting institutions like Observadores del Mar, IMEDMAR-UCV, or IRTA could contribute significantly to their conservation efforts.
Conclusion: Preserving a Marine Treasure
As you can imagine, each noble pen shell is crucial for the species’ recovery, especially if it is found in open seas, as it could be a specimen resistant to the disease. Despite the high mortality rates, hope is not lost that these individuals exist, but the vastness of the sea compared to the few survivors complicates the chances of finding them. Therefore, the collaboration of those who dive, fish, or simply snorkel in the sea is essential. If you want to participate in this needle-in-a-haystack search and spot any noble pen shell during your underwater activities, try to take photographs and note the GPS location, and do not hesitate to contact institutions such as Observadores del Mar (observadoresdelmar@icm.csic.es), the Institute of Environmental and Marine Sciences Research (IMEDMAR-UCV) (imedmar@ucv.es), or the Institute of Agrifood Research and Technology (IRTA) (patricia.prado@irta.cat), among others.
References
As always, here are the main scientific articles we consulted for this piece:
Basso, L., Vazquez-Luis, M., Garcia-March, J.R., Deudero, S., Alvarez, E., Vicente, N., Duarte, C.M. and Hendriks, I.E. (2015). The Pen Shell, Pinna nobilis: A review of population status and recommended research priorities in the Mediterranean Sea. Advances in Marine Biology, Vol 71, 109-160.
Catanese, G. (2020). An emergency situation for pen shells in the Mediterranean: the Adriatic Sea, one of the last Pinna nobilis shelters, is now affected by a mass mortality event. Journal of Invertebrate Pathology, 107388.
García-March, J., Tena, J., Hernandis, S., Vázquez-Luis, M., López, D., Téllez, C., Prado, P., Navas, J., Bernal, J. and Catanese, G. (2020). Can we save a marine species affected by a highly infective, highly lethal, waterborne disease from extinction? Biol. Conserv. 243, 108498.
Kersting, D., Benabdi, M., Čižmek, H., Grau, A., Jimenez, C., Katsanevakis, S., Öztürk, B., Tuncer, S., Tunesi, L., Vázquez-Luis, M., Vicente, N. and Otero Villanueva, M. (2020). Pinna nobilis. The IUCN Red List of Threatened Species 2019: e.T160075998A160081499.
Panarese, R., Tedesco, P., Chimienti, G., Latrofa, M.S., Quaglio, F., Passantino, G., Buonavoglia, C., Gustinelli, A., Tursi, A. and Otranto, D. (2019). Haplosporidium pinnae associated with mass mortality in endangered Pinna nobilis (Linnaeus 1758) fan mussels. Journal of Invertebrate Pathology 164, 32-37.
Vázquez-Luis, M., Álvarez, E., Barrajón, A., García-March, J.R., Grau, A., Hendriks, I.E., Jiménez, S., Kersting, D., Moreno, D., Pérez, M., Ruiz, J.M., Sánchez, J., Villalba, A. and Deudero, S. (2017). S.O.S. Pinna nobilis: A mass mortality event in western Mediterranean Sea. Frontiers in Marine Science 4(220), 109.
Original text by Sebastián Hernandis Caballero – Oceanógrapher – for Three Knots Magazine
Discover more ocean-inspired articles like this in Just the Sea’s Journal. Delve deeper into the wonders of marine life and conservation efforts across the world’s oceans.
Explore the Ecological Role of the “Nacra” Noble Pen Shell (Pinna Nobilis) in the Mediterranean
Introduction: Discovering the Noble Pen Shell
The noble pen shell, known as Pinna nobilis, is an emblematic and endemic species of the Mediterranean Sea; meaning, it cannot be found anywhere else in the world. It is the largest bivalve mollusk in this sea and the second longest in the world, reaching up to 1.2 meters in length, surpassed only by the tropical species Tridacna gigas. Despite its rapid growth (able to exceed 20 centimeters in its first 2 years), it remains relatively unknown.
Specimen of noble pen shell (Pinna nobilis) among the leaves of the seagrass Posidonia (Posidonia oceanica) in Calpe. Photo: Sebastián Hernandis.
Emblem of the Mediterranean: Size and Significance
It’s true that bivalves are a less popular group compared to the charm of turtles or dolphins. Moreover, being second in something can often mean being forgotten—think of the second man to walk on the moon. Being an endemic species highlights its value, but it logically makes it less known in places where it is not present.
Natural History and Ecological Role of the Largest Bivalve Mollusk in the Mediterranean
Due to its large size, the noble pen shell has few natural predators, with adult specimens only threatened by strong storms or octopuses. The former can be lethal due to strong hydrodynamics, while the latter are among the few animals capable of prying open their shells through sheer force, though this isn’t an easy battle for them. The noble pen shell is a filter feeder, relying on passing water through its gills to capture food. In English, it’s known as the “fan mussel,” due to its triangular fan-shaped shell. In its natural habitat, we typically see only about two-thirds of its total size, as the last third is buried in the substrate, anchored to the seabed by fibers known as byssus.
Octopus (Octopus vulgaris) with a noble pen shell (Pinna nobilis) shell. Octopuses are among the few predators of noble pen shells. In this case, it is using a shell of a deceased noble pen shell to cover itself in its hole. Photo: Sebastián Hernandis.
There’s limited research, but it’s known these animals are hermaphrodites, able to mature both reproductive organs asynchronously during breeding season. To reproduce, they release gametes into the water, relying on chance and natural selection for fertilization and larval survival. There’s suspicion that there may be some synchronization mechanism among individuals for group gamete emission.
Their habitat ranges from shallow areas at 1-2 meters deep to 50 meters, usually within meadows of the seagrass Posidonia oceanica, another endemic and iconic species shaping one of the Mediterranean’s most distinctive ecosystems.
Specimen of noble pen shell (Pinna nobilis) among the leaves of the seagrass Posidonia (Posidonia oceanica) in Moraira. Photo: Sebastián Hernandis.
Threats to Survival: Disease and Environmental Degradation
Until a few years ago, noble pen shells were relatively easy to spot among Posidonia leaves due to their size. However, since late 2016, a disease caused by a previously unknown protozoan has decimated populations in the southern Spanish Mediterranean. This protozoan, Haplosporidium pinnae, quickly spread via currents throughout the Mediterranean, resulting in near 100% mortality in affected populations. The noble pen shell’s situation is critical, leading the International Union for Conservation of Nature (IUCN) to declare it critically endangered.
Few populations remain free from this parasite. In Spain, only two surviving populations are known, located in the Ebro Delta and the Mar Menor. Why these populations have remained healthy is unknown, though partial isolation from open seas and specific physicochemical conditions (like salinity) might prevent parasite entry. Despite their survival so far, the future looks bleak for the species in terms of recovery. No individuals resistant to the disease have been found, and the protozoan’s persistence could prevent Mediterranean populations from recovering.
Several specimens of noble pen shell (Pinna nobilis) in the Posidonia (Posidonia oceanica) meadow in Calpe. Photo: Sebastián Hernandis.
Conservation Efforts: A Call to Action
Adding to the challenge, the Mar Menor—a sanctuary for these giant mollusks—is facing an environmental crisis due to agricultural pollution and unchecked urban development, which could deliver a final blow to a species already on life support.
Each noble pen shell is crucial to the species’ recovery, especially those in open seas, as they might hold the key to disease resistance. Despite high mortality rates, hope remains that such individuals exist, yet the vastness of the sea versus the few survivors complicates finding them. Therefore, collaboration from divers, fishermen, and snorkelers is crucial. If you spot a noble pen shell during your underwater activities, taking photos, noting GPS coordinates, and contacting institutions like Observadores del Mar, IMEDMAR-UCV, or IRTA could contribute significantly to their conservation efforts.
Conclusion: Preserving a Marine Treasure
As you can imagine, each noble pen shell is crucial for the species’ recovery, especially if it is found in open seas, as it could be a specimen resistant to the disease. Despite the high mortality rates, hope is not lost that these individuals exist, but the vastness of the sea compared to the few survivors complicates the chances of finding them. Therefore, the collaboration of those who dive, fish, or simply snorkel in the sea is essential. If you want to participate in this needle-in-a-haystack search and spot any noble pen shell during your underwater activities, try to take photographs and note the GPS location, and do not hesitate to contact institutions such as Observadores del Mar (observadoresdelmar@icm.csic.es), the Institute of Environmental and Marine Sciences Research (IMEDMAR-UCV) (imedmar@ucv.es), or the Institute of Agrifood Research and Technology (IRTA) (patricia.prado@irta.cat), among others.
References
As always, here are the main scientific articles we consulted for this piece:
Original text by Sebastián Hernandis Caballero – Oceanógrapher – for Three Knots Magazine
Discover more ocean-inspired articles like this in Just the Sea’s Journal. Delve deeper into the wonders of marine life and conservation efforts across the world’s oceans.