4 research outputs found
Unexpected residual habitats raise hope for the survival of the fan mussel Pinna nobilis along the Occitan coast (Northwest Mediterranean Sea)
In 2019, the status of the Mediterranean fan mussel Pinna nobilis was elevated to
‘Critically Endangered’ on the IUCN Red List, in response to the pandemic caused by the parasite
Haplosporidium pinnae. Identifying refuge habitats, free from parasites, is critical to the survival
of the mussel. The distribution of P. nobilis was investigated along the Occitan coast (Northwest
Mediterranean Sea) because of the presence of a unique lagoonal system that may provide potential
refuges. Interviews with users and managers were conducted to identify target zones where
the species was sighted. In situ surveys were carried out to define the main aggregations of fan
mussels and characterize the habitat. Line transects were deployed to count and measure individuals
to estimate density, abundance, and size distribution. Population densities were variable,
ranging from 0.6 ± 0.2 (SE) to 70.8 ± 7.6 ind. 100 m−2, representing one of the highest densities re -
ported in the Mediterranean Sea. The total abundance of individuals across the coast was extra -
polated to 163 000, with 87% located in Thau and Salses-Leucate, highlighting these lagoons as
essential for the survival of the species. This study also revealed the diversity of habitats colonized
by P. nobilis. In the context of the pandemic, only the lagoon populations remain unaffected and
provide natural refuges that have disappeared from all open-water coastal areas. However, the
conditions in these lagoons could become unfavorable, leading to the collapse of the last P. nobilis
populations. We therefore propose that Thau and Salses-Leucate lagoons, which harbor the
largest remaining populations of P. nobilis, should be declared as conservation priorities.En prens
Investigating population dynamics from parentage analysis in the highly endangered fan mussel Pinna nobilis
Understanding dispersal patterns is a major focus for conservation biology as it influences
local survival and resilience in case of local disturbance, particularly for sessile
species. Dispersal can be assessed through parentage analyses by estimating family
structure and self-recruitment.
This study documents the family structure of a pelagic
spawner, Pinna nobilis, which is facing a major crisis that threatens its survival as most
of its populations have been decimated by a parasite, Haplosporidium pinnae. In this
context, we focused on a single population (Peyrefite, Banyuls-sur-
mer,
France) where
640 individuals were sampled in 2011, 2015, and 2018 and genotyped for 22 microsatellite
markers. Genetic diversity was high and homogeneous among years, with
mean allele numbers ranging between 13.6 and 14.8 and observed heterozygosities
(Ho) between 0.7121 and 0.7331. Low, but significant, genetic differentiations were
found between 2011–2015
and 2015–2018.
A parentage analysis described 11 clusters,
including one prevailing, and revealed that 46.9% of individuals were involved in
half-sib
relationships, even between years, suggesting that source populations were
recurrent year after year. There were few individuals resampled between years (30
in 2015 and 14 in 2018), indicating a rapid turnover. Considering the large number
of half-sib
relationships but the low number of relations per individual, we conclude
that P. nobilis exhibit homogeneous reproductive success. Self-recruitment
was not
detected, making this population highly vulnerable as replenishment only relies on
connectivity from neighboring populations. In the context of the pandemic caused by
H. pinnae, these results will have to be considered when choosing a location to reintroduce
individuals in potential future rescue plans.En prensa
Genetic homogeneity of the critically endangered fan mussel, Pinna nobilis, throughout lagoons of the Gulf of Lion (North‑Western Mediterranean Sea)
The fan mussel, Pinna nobilis, endemic to the Mediterranean Sea, is a critically endangered species
facing mass mortality events in almost all of its populations, following the introduction of the parasite
Haplosporidium pinnae. Such a unique pandemic in a marine organism, which spreads rapidly and
with mortality rates reaching up to 100%, could lead to the potential extinction of the species. Only
few regions, involving lagoon habitats, remain healthy throughout the entire Mediterranean Sea.
This study describes the genetic structure of P. nobilis across the Gulf of Lion, including confined
locations such as lagoons and ports. A total of 960 samples were collected among 16 sites distributed
at 8 localities, and then genotyped using 22 microsatellite markers. Genetic diversity was high in all
sites with mean allele numbers ranging between 10 and 14.6 and with observed heterozygosities (Ho)
between 0.679 and 0.704. No genetic differentiation could be identified (FST ranging from 0.0018 to
0.0159) and the percentages of related individuals were low and similar among locations (from 1.6 to
6.5%). Consequently, all fan mussels, over the entire coastline surveyed, including those in the most
geographically isolated areas, belong to a large genetically homogeneous population across the Gulf
of Lion. Considering the ongoing mass mortality context, this result demonstrates that almost all of
the genetic diversity of P. nobilis populations is still preserved even in isolated lagoons, which might
represent a refuge habitat for the future of the species.En prensa2,92
Wide-Geographic and Long-Term Analysis of the Role of Pathogens in the Decline of Pinna nobilis to Critically Endangered Species
A mass mortality event (MME) affecting the fan mussel Pinna nobilis was first detected in Spain in autumn 2016 and spread north- and eastward through the Mediterranean Sea. Various pathogens have been blamed for contributing to the MME, with emphasis in Haplosporidium pinnae, Mycobacterium sp. and Vibrio spp. In this study, samples from 762 fan mussels (necropsies from 263 individuals, mantle biopsies from 499) of various health conditions, with wide geographic and age range, taken before and during the MME spread from various environments along Mediterranean Sea, were used to assess the role of pathogens in the MME. The number of samples processed by both histological and molecular methods was 83. The most important factor playing a main role on the onset of the mass mortality of P. nobilis throughout the Mediterranean Sea was the infection by H. pinnae. It was the only non-detected pathogen before the MME while, during MME spreading, its prevalence was higher in sick and dead individuals than in asymptomatic ones, in MME-affected areas than in non-affected sites, and it was not associated with host size, infecting both juveniles and adults. Conversely, infection with mycobacteria was independent from the period (before or during MME), from the affection of the area by MME and from the host health condition, and it was associated with host size. Gram (-) bacteria neither appeared associated with MME.En prens