The mass mortality of blue mussels (Mytilus spp.) from the Atlantic coast of France is associated with heavy genomic abnormalities as evidenced by flow cytometry

Abstract

Since 2014, France's blue mussel industry has been facing heavy mortality outbreaks (90-100%) affecting both juveniles and adults. This report presents evidence of heavy genomic abnormalities associated with mortality outbreaks in blue mussels, Mytilus edulis-galloprovincialis, from the Atlantic coast of France. In this study, ploidy characteristics of hemic cells were investigated using Flow CytoMetry (FCM), revealing an unusual, broad continuum of ploidy distribution from hypodiploidy to tetraploidy. FCM was additionally used to evaluate, at individual and populations levels, different thresholds of genomic abnormality (GA%) using the percentage of non-diploid nuclei. Individual mussels were considered to be abnormal when more than 10% of hemocytes in S-G2/M phase were present. At the population level, a threshold of 6% for the mean intensity of the abnormality is proposed, which means in the population, more than 6% of individual mussels have to present with more than 10% of their hemocytes in S-G2/M phase. GA% was found to be significantly predictive of the final mortality. Based on the established thresholds, only two mussel stocks analyzed in this study were considered to have good cytogenetic quality, while all other stocks appeared to be affected. FCM offers a very powerful tool to help manage current blue mussel mortality in France. We also believe that annual and extensive determination of cytogenetic quality of wild and cultivated mussel beds along with exclusive use of FCM-qualified mussel seeds should be a priority.

High mortality of mussels in northern Brittany – Evaluation of the involvement of pathogens, pathological conditions and pollutants

“…Mass mortalities of various bivalve species have been associated with disseminated neoplasia (see reviews by Elston et al, 1992;Carballal et al, 2015). In France, Benabdelmouna & Ledu (2016) observed that genomic abnormalities, namely aneuploidy of the hemolymph cells, were significantly correlated with…”

“…(Moore et al, 1991), including M. trossulus in Washington and Oregon (USA) and in British Columbia (Canada) (Elston et al, 1992). In France, Benabdelmouna & Ledu (2016) and Benabdelmouna et al (2018) presented evidence of the involvement of genomic abnormalities in mortality outbreaks in blue mussels and linked them to disseminated neoplasia. In addition, some cases of disseminated neoplasia in Mytilus edulis from Lannion (northern Brittany, France) were observed in mid-October 2016 by Burioli et al (2017) during a mortality event.…”

Mortality investigation of Mytilus edulis and Mytilus galloprovincialis in France: An experimental survey under laboratory conditions

“…Meanwhile, their roles on mortality outbreak in French cultured mussel populations are still unknown. In addition, recent studies indicated that the mortality level of blue mussel stocks in France appeared to be significantly correlated to genomic abnormalities detected by flow cytometric analyses of hemolymph (Benabdelmouna and Ledu 2016). These genomic abnormalities could be reflected environmental contaminations or also could be the sign of a potential disseminated neoplasia disease.…”

Potential environmental drivers of a regional blue mussel mass mortality event (winter of 2014, Breton Sound, France)

“…Work is still on progress regarding these hydrodynamic-pathological linked aspects of the winter 2014 mortality event. Very recently, a studied carried out by Benabdelmouna and Ledu (2016) reported heavy genomic abnormalities (GA) associated with blue mussel mortality outbreaks observed in March of 2014 in the sound. They particularly showed that mussel cultivated stocks with high GA% values presented high mortality levels.…”