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A partnership to save the fan mussel: an urgent response from scientists to the pandemic sweeping the Mediterranean

IRTA is participating in LIFE PINNARCA, a European project for the conservation and restoration of populations of fan mussels, which are critically endangered because of a protozoan parasite that has been causing them to die in huge numbers since 2016

The measures to be taken at different sites on the Mediterranean coastline include survivor censuses, comparative genomics, captive breeding, and reintroduction in optimal locations

Due to its low salinity, the Ebro Delta, the focal point of IRTA’s research, is one of the fan mussel’s last strongholds

The conservation status of a species can change in just a few months. The Mediterranean’s largest bivalve mollusc, the fan mussel (Pinna nobilis), is currently critically endangered, according to the International Union for Conservation of Nature (IUCN), owing to a pandemic that has caused the death of huge numbers of the species since 2016. Sea currents enabled the protozoan Haplosporidium pinnae to quickly spread from south-east Spain to virtually the whole of the Mediterranean coastline, where it has subsequently wiped out 99.9% of fan mussel populations. In response, the Institute of Agrifood Research and Technology (IRTA) teamed up with seven other Mediterranean research centres in 2021 to try to prevent the species from dying out entirely. Pinning its hopes on the few resistant fan mussels and remaining populations, the European project LIFE PINNARCA aims to take urgent measures for the protection and active recovery of the species in selected areas along the coasts of Spain, France, Italy and Greece. “A situation as critical as this, with a very important species heading for total extinction, requires large-scale coordination,” says Patricia Prado, a researcher from IRTA’s Marine and Inland Waters programme.

Also known as the noble pen shell, the fan mussel is endemic to the Mediterranean, where it mainly lives in Posidonia meadows in the open sea and in beds of dwarf eelgrass and Caulerpa prolifera seaweed in coastal lagoons and bays. Fan mussels play an important role in their ecosystems, as they filter water and hundreds of species live on their shells. With adult specimens growing to over a metre in length, they face risks caused by human activity, including anchoring, pollution, trawling, and habitat destruction for infrastructure construction. Their vulnerability to such threats has always affected the size of their populations, but protective measures had enabled them to recover well up until the outbreak of the disease. Almost six years later, the pathogen is still killing a great many fan mussels, sparing only a few, scattered individuals that may be resistant to it in open water and a handful of populations in coastal reservoirs and bays.

One of the fan mussel’s few remaining sanctuaries in Spain is the inner part of Alfacs Bay in the Ebro Delta, where, in 2014, IRTA registered 90,000 specimens, the Mediterranean’s second largest population. According to Prado’s team, the bay normally has a relatively low salinity level thanks to the inflow of irrigation water, something that could be acting as an obstacle to the protozoan and, thus, preventing the spread of infection. In the northern half of the delta, Fangar Bay had been exceptionally unaffected due to its low salinity, but Storm Gloria did away with 97.7% of its fan mussels in 2020. In any case, the post-pandemic map is not yet complete and new survivors have been detected in previously unexplored areas of the bay. “We don’t know how many fan mussels there still are; we need to carry out exhaustive, extensive sampling in the bays,” states Prado. With that in mind, one of the first LIFE PINNARCA activities in which IRTA will be participating is a fan mussel census in areas of shallow water, such as the Ebro Delta. Other organizations will be sweeping areas of open sea, including the Cap de Creus, the Medes Islands and the Costa Daurada.

Verifying the presence of survivors is not enough to guarantee the fan mussel’s future, however. “If only isolated, unconnected populations are left, it will be very difficult for them to reproduce, because of problems with consanguinity and vulnerability to the effects of human activity, as in the case of the environmental disaster in the Mar Menor; hence the need for joint management and population-crossing programmes,” explains Prado. Accordingly, LIFE PINNARCA is aiming to bring the species back from the brink through a range of coordinated measures in the field and in laboratories. Larvae spawned by adult fan mussels will be caught in net collectors and the juveniles will be kept in aquariums until they are large enough to be returned to the open sea. Captive breeding is a critical aspect, with larvae having yet to be successfully produced in such conditions. “Managing to close the fan mussel’s life cycle is vital,” stresses Prado. Doing so would make it possible to populate new reservoirs and repopulate existing ones, as well as to breed specimens resistant to the pathogen to obtain new generations with widespread immunity.

Fan mussel (Pinno nobilis).

At the same time, tests will be carried out in tanks with healthy adults to study how their survival is affected by environmental variables, such as salinity and temperature, and to analyse possible treatments for the disease, including antibiotics and antiprotozoals. Scientists will also attempt to identify mechanisms of resistance to the pathogen by using comparative genomics with samples of resistant and infected fan mussels and Pinna rudis, which is the bivalve most closely related to the fan mussel and is immune to the disease.

Conservation measures

In any case, while science is developing alternatives, protecting existing fan mussel populations in the wild is crucial to prevent their extinction. To that end, LIFE PINNARCA has designed a number of specific solutions for the short and medium terms. As far as the Ebro Delta is concerned, fan mussels protruding from the water on sandbanks and at risk of drying out will shortly be moved to deeper, safer spots. Additionally, there are plans to install fences formed by plant material on the northern side of Alfacs Bay, to act as a kind of green filter for the rice fields’ drains, removing sediment and nutrients and improving water quality. This, along with restrictions on sailing, is part of a package of environmental measures intended to reduce the dangers arising from human activity.

The project’s last line of work emphasizes awareness-raising and information. Steps will thus be taken to make people more conscious of the fan mussel’s plight, in the hope of reducing collisions with boats, vandalism and illegal harvesting. Furthermore, full data on populations will be made available to scientists and authorities on the LIFE PINNARCA website. The overall aim is to involve more decision makers and actors in a shared transnational cause: taking action before the Mediterranean loses one of its most emblematic creatures.

About the project

The LIFE Programme, the European Union’s funding instrument for supporting projects involving the environment, nature conservation and climate action, is contributing to the LIFE PINNARCA project. Having started in October 2021, LIFE PINNARCA is scheduled to run until December 2024. It is being carried out by an association comprising IRTA and the Institute of Environmental and Marine Science Research (IMEDMAR-UCV), the Mediterranean Institute for Advanced Studies (IMEDEA), the Murcia branch of Ecologists in Action, the Paul Ricard Oceanographic Institute, the University of Alicante, the University of the Aegean, and the University of Naples Federico II.