Pinna nobilis in the Greek seas (NE Mediterranean): on the brink of extinction?

Abstract

The Mediterranean endemic fan mussel Pinna nobilis is suffering an ongoing basin-scale mass mortality event (MME) since 2016. As most Mediterranean populations have collapsed, the species has been declared as Critically Endangered in the IUCN Red List of threatened species. In an effort to track the progress of the MME and provide updated information on the status of the species in the Greek seas, we compiled data collected through dedicated surveys and opportunistic assessments during 2019 and 2020. A total of 14589 fan mussel individuals, of which 81.1% dead, were recorded in 258 site surveys. Of the remaining 2762 live individuals, 256 were juveniles. Two marine areas which still sustain living populations were identified, namely Kalloni Gulf (Lesvos Island), and Laganas Bay (Zakynthos Island). The inner part of Kalloni Gulf appears to maintain the largest surviving population of the species in the eastern Mediterranean, with an abundance estimate of 684000 individuals (95% confidence interval: 322000-1453000). Solitary, potentially resistant, scattered individuals were recorded in several sites. Other previously abundant populations that had been assessed in the past, specifically those of Lake Vouliagmeni (Korinthiakos Gulf), Souda Bay (Crete) and Gera Gulf (Lesvos Island), and which collectively summed up to ~350,000 individuals, have now been wiped out. Our results document the collapse of most P. nobilis populations throughout the Greek seas. The MME has substantially progressed between early 2019 and mid-2020, as indicated by the increase of mortality at sites consecutively monitored multiple times. This work highlights the urgent need for continuous monitoring of surviving populations and calls for the immediate implementation of an effective protection and management strategy that will ensure the persistence of surviving individuals and the production of resistant offspring.

Recruitment Disruption and the Role of Unaffected Populations for Potential Recovery After the Pinna nobilis Mass Mortality Event

“…Altogether, our results show a worrying scenario for the species and highlight the importance of unaffected P. nobilis populations as larval exporting sites, which could play a main role in a potential, although probably slow, recovery. This applies as well to the Adriatic and Eastern Mediterranean Seas, where unaffected populations are being described as the MME spreads eastwards (Kersting et al, 2019;Čižmek et al, 2020;Zotou et al, 2020). In addition, (1) the status "unaffected" is not static and these sites could be affected by the mortality in the near future (e.g., Alfacs Bay, Prado et al, 2019); and (2) some of these unaffected sites are highly anthropized and subjected to multiple stressors that may cause mortalities on their own (e.g., Mar Menor, García-Ayllon, 2018).…”

“…Most known and studied P. nobilis populations in the Western Mediterranean Sea have almost completely disappeared, with mortality rates exceeding 90% (Vázquez-Luis et al, 2017;Panarese et al, 2019;García-March et al, 2020) and populations in the Eastern Mediterranean and Adriatic Sea are suffering the same fate (Katsanevakis et al, 2019;Kersting et al, 2019;Cižmek et al, 2020;Öndes et al, 2020;Özalp and Kersting, 2020). There is the exception, however, of several sites with very specific environmental settings where P. nobilis populations remain unaffected to date: Fangar Bay (Delta del Ebro, Spain), Mar Menor (Spain), Rhône Delta (France), Etang de Thau (France), Diana and Urbino pools (Corsica, France), Venice lagoon (Italy), inner Kalloni Gulf (Greece) (Catanese et al, 2018;Cabanellas-Reboredo et al, 2019;Kersting et al, 2019;Simide et al, 2019;Prado et al, 2019;Foulquie et al, 2020;Zotou et al, 2020). This worrying scenario has led to the recent inclusion of the species as Critically Endangered on the IUCN Red List (Kersting et al, 2019).…”

The Implication of Vibrio Bacteria in the Winter Mortalities of the Critically Endangered Pinna nobilis

“…Mycobacterium species were detected alongside H. pinnae in the Tyrrhenian Sea (Mediterranean) in moribund individuals of P. nobilis , causing strongly inflammatory lesions, and were proposed as a new potential threat for the populations of fan mussels [ 14 ]. Meanwhile, the detection of H. pinnae persisted in mortalities in the Ionian and Aegean Sea, having a great negative impact on populations of fan mussels and causing the change of the ranking of the species in the Mediterranean Sea to Critically Endangered according to the IUCN red list [ 15 , 16 , 17 , 18 , 19 , 20 , 21 ]. Both aforementioned pathogens have been detected in P. nobilis populations suffering from mortalities on Croatian coastlines, thus invading the last safe shelter of the species from the mortalities that occurred in the rest of Mediterranean Sea [ 22 , 23 ].…”

“…In the context of continuous mortalities in Greece, the current study was conducted in order to assess the status of the remaining P. nobilis populations in Greek territory. After the collapse of fan mussel populations in Thermaikos gulf, Thessaloniki [ 19 ], the remaining populations with the highest density, which were chosen for investigation, were the populations in Kalloni gulf, Lesvos Island and Maliakos gulf, Fthiotis ( Figure 1 ). The main objectives of this study were (a) the monitoring of the two remaining populations in Greece regarding haplosporidian and mycobacteria parasites during the winter months; (b) identification of other harmful bacteria such as Vibrio spp.…”

Population trends of the fan mussel Pinna nobilis from Portofino MPA (Ligurian Sea, Western Mediterranean Sea) before and after a mass mortality event and a catastrophic storm

“…A highly species-specific newly described protozoan parasite, Haplosporidium pinnae, has been reported as the likely cause of the fan mussel mortality (Darriba 2017;Vázquez-Luis et al 2017;Catanese et al 2018;García-March et al 2020). Lately, in 2017, other mass mortality events were recorded from Corse (France) and Italy (Catanese et al 2018; citizen science at http://www.observa doresdelmar.es), and even from the Eastern Mediterranean basin, with an average mortality of more than 93% of the Lesvos Island (Aegean Sea) population (Katsanevakis et al 2019) and a general mortality rate of 31% in the Greek seas (Zotou et al 2020). The spreading of the parasite in the western Mediterranean basin has been related to the action of surface currents (Cabanellas-Reboredo et al 2019;García-March et al 2020).…”