Mother-of-pearl survives on the verge of extinction

BarcelonaThe mother-of-pearl happily populated the Mediterranean Sea not so many years ago. Molluscs in the form of giant spans that can reach more than a meter high lived on the seabed of Catalonia, the Balearic Islands, Alicante, Murcia and Almeria. The situation of the species, which had millions of specimens, has taken a fateful turn and today it is not striking for its iconic appearance but because it is in a kind of time trial to ensure its survival. The appearance of a parasite just six years ago has wiped out the species from almost every place where scientists documented it. “A very pandemic beast,” sums up IRTA researcher Patricia Prado. Today, mother-of-pearl survives in two small strongholds, the Ebro delta and the Mar Menor, where the salinity of the water shields them, but where they also face other dangers, such as the loss of their habitats and crises. which have further reduced populations to near-testimonial figures in some cases.

“It’s an extremely serious situation. We’ve never seen a mass mortality like this.” Prado describes to ARA the impact they have already been able to check on the parasitic protozoan (Haplosporidium pinnae) that broke into the Mediterranean in 2016 and has liquidated entire populations. “In Portlligat, for example, we had marked nacre populations and in a matter of two months they all disappeared,” laments the researcher only as a small example of the drama that has been experienced in the open waters of the Mediterranean. Mortality rates once the pathogen is detected are close to 100%, so it can be said that the surviving populations are literally cornered and in places a little more protected from the entry of the parasite such as Alfacs Bay or lagoon of the Mar Menor in Murcia.

Recently, the mother-of-pearl has not been able to rest (Pinna nobilis). The storm Gloria, which hit the Ebro delta, devastated much of the parasite-free subsistence population in Fangar Bay. Days later, only twelve of the 533 registered were detected. In Alfacs Bay, where the other large colony remains, although it is not known for sure how large it is, the exterminating intruder has already been detected and mortality has been concentrated mainly in the areas. closer to the connection with the open sea, while inland it seems to have slowed the advance. Scientists know very little about this threat, but there is one that is very clear: when the salinity is lower than usual – it goes to the Ebro delta – or higher – this is the case of Mar Menor, a hypersaline lagoon – the parasite has a harder time surviving. This condition helps to save time and that is why the IRTA and the University of Alicante have ongoing projects that ensure the conservation of the species and the transfer of specimens to safe places while the vaccine which guarantees its survival.

The ‘green soup’ to the Mar Menor

The reality in the Mar Menor is not much more optimistic than in the Ebro delta and the recent mortality rate is frightening due, in this case, to the serious environmental crisis that has manifested itself in the form of episodes of mass mortality of fish in the lagoon. 2016 was the first episode of what was described as one green soup: Excess nutrients in the water from much of the intensive agriculture caused a lack of oxygen that killed 85% of the bottom of the lagoon, including the large population of mother-of-pearl. “It was a point of no return and the beginning of a process from which the Mar Menor has not recovered,” said Francisca Giménez Casalduero, a professor at the University of Alicante. If a 2015 study suggested that there were 1.6 million mother-of-pearl in the Mar Menor, the largest population in Spain, after the severe eutrophication episode five years ago, no more than 5,000 survived, adds the director of the Marine Research Center in Santa Pola.

An IRTA researcher with a specimen of mother-of-pearl surviving in the Ebro delta.

The 2016 crisis in the Mar Menor, therefore, devastated 99% of the local mother-of-pearl population, just as the exterminating parasite of the species was beginning to be detected elsewhere in the open sea. The second major critical episode in the lagoon came in 2019, after the torrential rains of the Dana, which pour a lot of fresh water – and loaded with nitrates – into the lagoon. “The deep layers turned into rotten water without oxygen, water that was loaded with sulfides and methane,” recalls the professor. “Even before we saw the dead fish, we detected a large concentration of species in the surface layers, precisely in the areas where the mother-of-pearl had survived in previous episodes. We didn’t know it yet, but what those fish were doing was fleeing.” add. Scientists were not in time to rescue them and mother-of-pearl was also a victim of the new environmental crisis. To all this is added the last episode of this past summer and all together it leaves the sad balance that the Mar Menor has gone from being the great refuge where the Pinna nobilis survived far from the parasite to be a place where “less than a thousand specimens remain,” laments Giménez.

Salinity acts as a shield

The survival of mother-of-pearl in the Ebro delta and the Mar Menor is partly explained by the salinity of the water, which slows down the expansion of the parasite that is killing them. With an average salinity of 36 to 39 ppt, the pathogen advances. In this sense, the levels normally below in the Delta and the levels normally above in the lagoon of the Mar Menor have so far been an ally.

Goal, captive breeding

With the wind clearly against it, scientists like Prado or Giménez do not have it easy to ensure the future of a species that contributes to marine biodiversity and also does a job of filtering water in the ecosystems where it lives. In the Ebro delta, they are mapping the study of salinity to try to ensure a safe habitat for the mother-of-pearl that still exists. The exact number is not clear, because the last population study that Prado did in 2010 spoke of 90,000 mother-of-pearl in the Alfacs area and it is assumed that the figure must already be much lower.

Both scientists are working with their teams and others in Europe on projects to secure the species through a program, Recupera Pinna, funded by the Biodiversity Foundation of the Ministry for Ecological Transition and the Barcelona Zoo Foundation for monitor existing populations, which provide valuable information, and use technology to measure salinity and water temperature and secure populations. “Save what you have and spot risk areas,” Prado sums up. In addition, the research also seeks to find specimens that may be resistant to the parasite to “find out how they survived.”

The future goal, however, is also to “close the life cycle of the species” and get it reproduced so that it can be reintroduced. Captive breeding, which has already taken its first steps in a project in the aquarium of the University of Murcia, is the challenge on the horizon and a passport, perhaps crucial, to move the mother-of-pearl away from the precipice of extinction. .


Source: Ara.cat – Portada by www.ara.cat.

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