Living under threat: Will one of the last Pinna nobilis populations be able to survive?

Abstract

1. The critically endangered fan mussel Pinna nobilis, endemic to the Mediterranean Sea, faces a drastic population decline all over the Mediterranean Sea owing to an infectious disease.2. Coastal lagoons represent one of this species' last reservoirs; thus, knowledge of the population conservation status in these ecosystems is essential.3. An extensive monitoring programme was conducted during 2014, 2017 and 2019 in the Mar Menor lagoon, a highly eutrophicated lagoon from Spain. On average, 32,535 m 2 have been surveyed each year to determine population densities, distributions and size structures.4. The cumulative impacts produced by intensive agriculture activity around the lagoon, together with a catastrophic meteorological phenomenon that occurred in 2019, have triggered a significant decline in fan mussel population densities and in population mean shell sizes over the years. Additionally, some fan mussels were infected by the protozoan Haplosporidium pinnae.5. Therefore, the current P. nobilis population from the Mar Menor is mainly composed of young individuals in specific areas that are facing an extreme situation. Urgent management and conservation actions focused on restoring the ecosystem and protecting P. nobilis individuals are urgently needed, together with reinforcement projects to increase the species' stock in one of its last reservoirs.

Wide-Geographic and Long-Term Analysis of the Role of Pathogens in the Decline of Pinna nobilis to Critically Endangered Species

“…Notably, the dynamics of haplosporidan parasites is modulated by environmental parameters, especially temperature and salinity (Burreson and Ford, 2004;Arzul and Carnegie, 2015). Specific tolerance of H. pinnae to temperature and salinity has been suggested (temperatures above 13.5 • C and salinity range between 36.5-39.7 psu; Cabanellas-Reboredo et al, 2019;García-March et al, 2020;Prado et al, 2021;Nebot-Colomer et al, 2021). Accordingly, salinity range outside the common Mediterranean salinity range (36.7-39.5 psu;Vidal-Vijande et al, 2011) is a shared feature of these coastal lagoons: on the one hand, the Mar Menor, exhibiting high salinity, up to 47 psu (Pérez-Ruzafa et al, 2005;Giménez-Casalduero et al, 2020); on the other hand, the other Spanish and French coastal lagoons, strongly affected by freshwater supplies (Prado et al, 2014(Prado et al, , 2020b.…”

Haplosporidium pinnae Parasite Detection in Seawater Samples

“…For this reason, we recommend intensive and periodic sampling in order to ensure that the coastal lagoons are truly free of the parasite. Cases of H. pinnae detection within some lagoons (sometimes referred to as sanctuaries) are also being observed and have been described as a consequence of parasite spread from open waters, resulting in enhanced mortalities in the outer region closer to the mouth of the lagoons or in the seaward vicinity of connecting channels [ 61 , 64 , 65 , 66 , 67 ]. In support of this, in 2018, the population in Alfacs Bay (South Ebro Delta) was infected only in its more external part located next to the open sea and subjected to higher salinities [ 68 ].…”

Reproduction of the endangered fan mussel Pinna nobilis under natural and captivity conditions

“…There are only a few survivors with potential resistance to the disease in the open waters of the entire Mediterranean Sea, scattered and usually distributed tens or hundreds of kilometres apart (Ruitton & Lefebvre, 2021) (http://www.observadoresdelmar.es, project NACRAS). Populations are only found in a few paralic environments (García‐March et al, 2020; Nebot‐Colomer et al, 2021; Peyran et al, 2021; Acarli, Acarli & Kale, 2022; Katsanevakis et al, 2022); that is, sedimentary environments such as coastal lagoons, deltas, and estuaries with a range of salinities from hypohaline to hyperhaline (Tagliapietra, Sigovini & Ghirardini, 2009). The occurrence of extreme salinities in some paralic environments compared with the open sea seems to preclude the introduction of the disease (Cabanellas‐Reboredo et al, 2019; Prado et al, 2021).…”

“…As a result of the harsher conditions in those habitats, shorter life expectancy has been reported for the individuals inhabiting them (García‐March et al, 2019). Moreover, the populations living in these locations have inconsistent reproductive success (Prado et al, 2020; Nebot‐Colomer et al, 2021) and rely mostly on the rain of propagules to maintain their numbers (Peyran et al, 2021). However, some recent recruitment events have been observed in the open sea, which give rise to hope for the recovery of the species (Kersting et al, 2020).…”